2020 |
Hartke, Thomas; Oreg, Botond; Jia, Ningyuan; Zwierlein, Martin Measuring total density correlations in a Fermi-Hubbard gas via bilayer microscopy Journal Article preprint arXiv:2003.11669, 2020. @article{hartke2020measuring, title = {Measuring total density correlations in a Fermi-Hubbard gas via bilayer microscopy}, author = {Thomas Hartke and Botond Oreg and Ningyuan Jia and Martin Zwierlein}, url = {https://arxiv.org/abs/2003.11669}, year = {2020}, date = {2020-03-01}, journal = {preprint arXiv:2003.11669}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Yan, Zoe Z; Park, Jee Woo; Ni, Yiqi; Loh, Huanqian; Will, Sebastian; Karman, Tijs; Zwierlein, Martin Resonant dipolar collisions of ultracold molecules induced by microwave dressing Journal Article preprint arXiv:2003.02830, 2020. @article{yan2020resonant, title = {Resonant dipolar collisions of ultracold molecules induced by microwave dressing}, author = {Zoe Z Yan and Jee Woo Park and Yiqi Ni and Huanqian Loh and Sebastian Will and Tijs Karman and Martin Zwierlein}, url = {https://arxiv.org/abs/2003.02830}, year = {2020}, date = {2020-03-01}, journal = {preprint arXiv:2003.02830}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2019 |
Altman, Ehud; Brown, Kenneth R; Carleo, Giuseppe; Carr, Lincoln D; Demler, Eugene; Chin, Cheng; DeMarco, Brian; Economou, Sophia E; Eriksson, Mark A; Fu, Kai-Mei C; Greiner, Markus; Hazzard, Kaden R A; Hulet, Randall G; Kollar, Alicia J; Lev, Benjamin L; Lukin, Mikhail D; Ma, Ruichao; Mi, Xiao; Misra, Shashank; Monroe, Christopher; Murch, Kater; Nazario, Zaira; Ni, Kang-Kuen; Potter, Andrew C; Roushan, Pedram; Saffman, Mark; Schleier-Smith, Monika; Siddiqi, Irfan; Simmonds, Raymond; Singh, Meenakshi; Spielman, I B; Temme, Kristan; Weiss, David S; Vuckovic, Jelena; Vuletic, Vladan; Ye, Jun; Zwierlein, Martin Quantum Simulators: Architectures and Opportunities Journal Article preprint arXiv:1912.06938, 2019. @article{altman2019quantum, title = {Quantum Simulators: Architectures and Opportunities}, author = {Ehud Altman and Kenneth R Brown and Giuseppe Carleo and Lincoln D Carr and Eugene Demler and Cheng Chin and Brian DeMarco and Sophia E Economou and Mark A Eriksson and Kai-Mei C Fu and Markus Greiner and Kaden R A Hazzard and Randall G Hulet and Alicia J Kollar and Benjamin L Lev and Mikhail D Lukin and Ruichao Ma and Xiao Mi and Shashank Misra and Christopher Monroe and Kater Murch and Zaira Nazario and Kang-Kuen Ni and Andrew C Potter and Pedram Roushan and Mark Saffman and Monika Schleier-Smith and Irfan Siddiqi and Raymond Simmonds and Meenakshi Singh and I B Spielman and Kristan Temme and David S Weiss and Jelena Vuckovic and Vladan Vuletic and Jun Ye and Martin Zwierlein}, year = {2019}, date = {2019-12-01}, journal = {preprint arXiv:1912.06938}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Fletcher, Richard J; Shaffer, Airlia; Wilson, Cedric C; Patel, Parth B; Yan, Zhenjie; Crépel, Valentin; Mukherjee, Biswaroop; Zwierlein, Martin W Geometric squeezing into the lowest Landau level Journal Article preprint arXiv:1911.12347, 2019. @article{fletcher2019geometric, title = {Geometric squeezing into the lowest Landau level}, author = {Richard J Fletcher and Airlia Shaffer and Cedric C Wilson and Parth B Patel and Zhenjie Yan and Valentin Crépel and Biswaroop Mukherjee and Martin W Zwierlein}, url = {https://arxiv.org/abs/1911.12347}, year = {2019}, date = {2019-11-01}, journal = {preprint arXiv:1911.12347}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Patel, Parth B; Yan, Zhenjie; Mukherjee, Biswaroop; Fletcher, Richard J; Struck, Julian; Zwierlein, Martin W Universal Sound Diffusion in a Strongly Interacting Fermi Gas Journal Article preprint arXiv:1909.02555, 2019. @article{Patel2019, title = {Universal Sound Diffusion in a Strongly Interacting Fermi Gas}, author = {Parth B Patel and Zhenjie Yan and Biswaroop Mukherjee and Richard J Fletcher and Julian Struck and Martin W Zwierlein}, url = {https://arxiv.org/abs/1909.02555}, year = {2019}, date = {2019-09-01}, journal = {preprint arXiv:1909.02555}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Christianen, Arthur; Zwierlein, Martin W; Groenenboom, Gerrit C; Karman, Tijs Photoinduced Two-Body Loss of Ultracold Molecules Journal Article Physical Review Letters, 123 (12), 2019, ISSN: 10797114. @article{Christianen2019, title = {Photoinduced Two-Body Loss of Ultracold Molecules}, author = {Arthur Christianen and Martin W Zwierlein and Gerrit C Groenenboom and Tijs Karman}, url = {http://arxiv.org/abs/1905.06846}, doi = {10.1103/PhysRevLett.123.123402}, issn = {10797114}, year = {2019}, date = {2019-05-01}, journal = {Physical Review Letters}, volume = {123}, number = {12}, abstract = {The lifetime of nonreactive ultracold bialkali gases was conjectured to be limited by sticky collisions amplifying three-body loss. We show that the sticking times were previously overestimated and do not support this hypothesis. We find that electronic excitation of NaK+NaK collision complexes by the trapping laser leads to the experimentally observed two-body loss. We calculate the excitation rate with a quasiclassical, statistical model employing ab initio potentials and transition dipole moments. Using longer laser wavelengths or repulsive box potentials may suppress the losses.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The lifetime of nonreactive ultracold bialkali gases was conjectured to be limited by sticky collisions amplifying three-body loss. We show that the sticking times were previously overestimated and do not support this hypothesis. We find that electronic excitation of NaK+NaK collision complexes by the trapping laser leads to the experimentally observed two-body loss. We calculate the excitation rate with a quasiclassical, statistical model employing ab initio potentials and transition dipole moments. Using longer laser wavelengths or repulsive box potentials may suppress the losses. |
Mukherjee, Biswaroop; Patel, Parth B; Yan, Zhenjie; Fletcher, Richard J; Struck, Julian; Zwierlein, Martin W Spectral Response and Contact of the Unitary Fermi Gas Journal Article Physical Review Letters, 122 (20), pp. 203402, 2019. @article{Mukherjee2019, title = {Spectral Response and Contact of the Unitary Fermi Gas}, author = {Biswaroop Mukherjee and Parth B Patel and Zhenjie Yan and Richard J Fletcher and Julian Struck and Martin W Zwierlein}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.122.203402}, doi = {10.1103/PhysRevLett.122.203402}, year = {2019}, date = {2019-05-01}, journal = {Physical Review Letters}, volume = {122}, number = {20}, pages = {203402}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Yan, Zoe Z; Ni, Yiqi; Robens, Carsten; Zwierlein, Martin W Bose polarons near quantum criticality Journal Article preprint arXiv:1904.02685, 2019. @article{Yan2019a, title = {Bose polarons near quantum criticality}, author = {Zoe Z Yan and Yiqi Ni and Carsten Robens and Martin W Zwierlein}, url = {http://arxiv.org/abs/1904.02685}, year = {2019}, date = {2019-04-01}, journal = {preprint arXiv:1904.02685}, abstract = {The emergence of quasiparticles in strongly interacting matter represents one of the cornerstones of modern physics. However, when different phases of matter compete near a quantum critical point, the very existence of quasiparticles comes under question. Here we create Bose polarons near quantum criticality by immersing atomic impurities in a Bose-Einstein condensate (BEC) with near-resonant interactions. Using locally-resolved radiofrequency spectroscopy, we probe the energy, spectral width, and short-range correlations of the impurities as a function of temperature. Far below the superfluid critical temperature, the impurities form well-defined quasiparticles. However, their inverse lifetime, given by their spectral width, is observed to increase linearly with temperature, a hallmark of quantum critical behavior. Close to the BEC critical temperature, the spectral width exceeds the binding energy of the impurities, signaling a breakdown of the quasiparticle picture near quantum criticality.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The emergence of quasiparticles in strongly interacting matter represents one of the cornerstones of modern physics. However, when different phases of matter compete near a quantum critical point, the very existence of quasiparticles comes under question. Here we create Bose polarons near quantum criticality by immersing atomic impurities in a Bose-Einstein condensate (BEC) with near-resonant interactions. Using locally-resolved radiofrequency spectroscopy, we probe the energy, spectral width, and short-range correlations of the impurities as a function of temperature. Far below the superfluid critical temperature, the impurities form well-defined quasiparticles. However, their inverse lifetime, given by their spectral width, is observed to increase linearly with temperature, a hallmark of quantum critical behavior. Close to the BEC critical temperature, the spectral width exceeds the binding energy of the impurities, signaling a breakdown of the quasiparticle picture near quantum criticality. |
Yan, Zhenjie; Patel, Parth B; Mukherjee, Biswaroop; Fletcher, Richard J; Struck, Julian; Zwierlein, Martin W Boiling a Unitary Fermi Liquid Journal Article Physical Review Letters, 122 (9), 2019, ISSN: 10797114. @article{Yan2019, title = {Boiling a Unitary Fermi Liquid}, author = {Zhenjie Yan and Parth B Patel and Biswaroop Mukherjee and Richard J Fletcher and Julian Struck and Martin W Zwierlein}, doi = {10.1103/PhysRevLett.122.093401}, issn = {10797114}, year = {2019}, date = {2019-03-01}, journal = {Physical Review Letters}, volume = {122}, number = {9}, publisher = {American Physical Society}, abstract = {We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy gives access to the energy, lifetime, and short-range correlations of Fermi polarons at low temperatures $T$. In this regime, we observe a characteristic $T^2$ dependence of the spectral width, corresponding to the quasiparticle decay rate expected for a Fermi liquid. At high $T$, the spectral width decreases again towards the scattering rate of the classical, unitary Boltzmann gas, $backslashpropto T^-1/2$. In the transition region between the quantum degenerate and classical regime, the spectral width attains its maximum, on the scale of the Fermi energy, indicating the breakdown of a quasiparticle description. Density measurements in a harmonic trap directly reveal the majority dressing cloud surrounding the minority spins and yield the compressibility along with the effective mass of Fermi polarons.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy gives access to the energy, lifetime, and short-range correlations of Fermi polarons at low temperatures $T$. In this regime, we observe a characteristic $T^2$ dependence of the spectral width, corresponding to the quasiparticle decay rate expected for a Fermi liquid. At high $T$, the spectral width decreases again towards the scattering rate of the classical, unitary Boltzmann gas, $backslashpropto T^-1/2$. In the transition region between the quantum degenerate and classical regime, the spectral width attains its maximum, on the scale of the Fermi energy, indicating the breakdown of a quasiparticle description. Density measurements in a harmonic trap directly reveal the majority dressing cloud surrounding the minority spins and yield the compressibility along with the effective mass of Fermi polarons. |
Nichols, Matthew A; Cheuk, Lawrence W; Okan, Melih; Hartke, Thomas R; Mendez, Enrique; Senthil, T; Khatami, Ehsan; Zhang, Hao; Zwierlein, Martin W Spin transport in a Mott insulator of ultracold fermions Journal Article Science, 363 (6425), pp. 383–387, 2019, ISSN: 10959203. @article{Nichols2019, title = {Spin transport in a Mott insulator of ultracold fermions}, author = {Matthew A Nichols and Lawrence W Cheuk and Melih Okan and Thomas R Hartke and Enrique Mendez and T Senthil and Ehsan Khatami and Hao Zhang and Martin W Zwierlein}, doi = {10.1126/science.aat4387}, issn = {10959203}, year = {2019}, date = {2019-01-01}, journal = {Science}, volume = {363}, number = {6425}, pages = {383--387}, publisher = {American Association for the Advancement of Science}, abstract = {Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole--assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole--assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model. |
2018 |
Rvachov, T M; Son, H; Park, J J; Notz, P M; Wang, T T; Zwierlein, M W; Ketterle, W; Jamison, A O Photoassociation of ultracold NaLi Journal Article Physical Chemistry Chemical Physics, 20 (7), 2018, ISSN: 14639076. @article{Rvachov2018b, title = {Photoassociation of ultracold NaLi}, author = {T M Rvachov and H Son and J J Park and P M Notz and T T Wang and M W Zwierlein and W Ketterle and A O Jamison}, doi = {10.1039/c7cp08480c}, issn = {14639076}, year = {2018}, date = {2018-01-01}, journal = {Physical Chemistry Chemical Physics}, volume = {20}, number = {7}, abstract = {textcopyright the Owner Societies 2018. We perform photoassociation spectroscopy in an ultracold 23 Na- 6 Li mixture to study the c 3 $Sigma$ + excited triplet molecular potential. We observe 50 vibrational states and their substructure to an accuracy of 20 MHz, and provide line strength data from photoassociation loss measurements. An analysis of the vibrational line positions using near-dissociation expansions and a full potential fit is presented. This is the first observation of the c 3 $Sigma$ + potential, as well as photoassociation in the NaLi system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright the Owner Societies 2018. We perform photoassociation spectroscopy in an ultracold 23 Na- 6 Li mixture to study the c 3 $Sigma$ + excited triplet molecular potential. We observe 50 vibrational states and their substructure to an accuracy of 20 MHz, and provide line strength data from photoassociation loss measurements. An analysis of the vibrational line positions using near-dissociation expansions and a full potential fit is presented. This is the first observation of the c 3 $Sigma$ + potential, as well as photoassociation in the NaLi system. |
Rvachov, T M; Son, H; Park, J J; Ebadi, S; Zwierlein, M W; Ketterle, W; Jamison, A O Two-photon spectroscopy of the NaLi triplet ground state Journal Article Physical Chemistry Chemical Physics, 20 (7), 2018, ISSN: 14639076. @article{Rvachov2018a, title = {Two-photon spectroscopy of the NaLi triplet ground state}, author = {T M Rvachov and H Son and J J Park and S Ebadi and M W Zwierlein and W Ketterle and A O Jamison}, doi = {10.1039/c7cp08481a}, issn = {14639076}, year = {2018}, date = {2018-01-01}, journal = {Physical Chemistry Chemical Physics}, volume = {20}, number = {7}, abstract = {textcopyright the Owner Societies 2018. We employ two-photon spectroscopy to study the vibrational states of the triplet ground state potential (a 3 $Sigma$ + ) of the 23 Na 6 Li molecule. Pairs of Na and Li atoms in an ultracold mixture are photoassociated into an excited triplet molecular state, which in turn is coupled to vibrational states of the triplet ground potential. Vibrational state binding energies, line strengths, and potential fitting parameters for the triplet ground a 3 $Sigma$ + potential are reported. We also observe rotational splitting in the lowest vibrational state.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright the Owner Societies 2018. We employ two-photon spectroscopy to study the vibrational states of the triplet ground state potential (a 3 $Sigma$ + ) of the 23 Na 6 Li molecule. Pairs of Na and Li atoms in an ultracold mixture are photoassociated into an excited triplet molecular state, which in turn is coupled to vibrational states of the triplet ground potential. Vibrational state binding energies, line strengths, and potential fitting parameters for the triplet ground a 3 $Sigma$ + potential are reported. We also observe rotational splitting in the lowest vibrational state. |
2017 |
Rvachov, Timur M; Son, Hyungmok; Sommer, Ariel T; Ebadi, Sepehr; Park, Juliana J; Zwierlein, Martin W; Ketterle, Wolfgang; Jamison, Alan O Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments Journal Article Physical Review Letters, 119 (14), pp. 143001, 2017, ISSN: 0031-9007. @article{Rvachov2017, title = {Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments}, author = {Timur M Rvachov and Hyungmok Son and Ariel T Sommer and Sepehr Ebadi and Juliana J Park and Martin W Zwierlein and Wolfgang Ketterle and Alan O Jamison}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.143001}, doi = {10.1103/PhysRevLett.119.143001}, issn = {0031-9007}, year = {2017}, date = {2017-10-01}, journal = {Physical Review Letters}, volume = {119}, number = {14}, pages = {143001}, abstract = {textcopyright 2017 American Physical Society. We create fermionic dipolar Na23Li6 molecules in their triplet ground state from an ultracold mixture of Na23 and Li6. Using magnetoassociation across a narrow Feshbach resonance followed by a two-photon stimulated Raman adiabatic passage to the triplet ground state, we produce 3×104 ground state molecules in a spin-polarized state. We observe a lifetime of 4.6 s in an isolated molecular sample, approaching the p-wave universal rate limit. Electron spin resonance spectroscopy of the triplet state was used to determine the hyperfine structure of this previously unobserved molecular state.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright 2017 American Physical Society. We create fermionic dipolar Na23Li6 molecules in their triplet ground state from an ultracold mixture of Na23 and Li6. Using magnetoassociation across a narrow Feshbach resonance followed by a two-photon stimulated Raman adiabatic passage to the triplet ground state, we produce 3×104 ground state molecules in a spin-polarized state. We observe a lifetime of 4.6 s in an isolated molecular sample, approaching the p-wave universal rate limit. Electron spin resonance spectroscopy of the triplet state was used to determine the hyperfine structure of this previously unobserved molecular state. |
Park, Jee Woo; Yan, Zoe Z; Loh, Huanqian; Will, Sebastian A; Zwierlein, Martin W Second-scale nuclear spin coherence time of ultracold 23 Na 40 K molecules Journal Article Science, 357 (6349), pp. 372–375, 2017, ISSN: 0036-8075. @article{Park2017, title = {Second-scale nuclear spin coherence time of ultracold 23 Na 40 K molecules}, author = {Jee Woo Park and Zoe Z Yan and Huanqian Loh and Sebastian A Will and Martin W Zwierlein}, url = {http://arxiv.org/abs/1606.04184 http://dx.doi.org/10.1126/science.aal5066 http://www.sciencemag.org/lookup/doi/10.1126/science.aal5066}, doi = {10.1126/science.aal5066}, issn = {0036-8075}, year = {2017}, date = {2017-07-01}, journal = {Science}, volume = {357}, number = {6349}, pages = {372--375}, abstract = {Coherence, the stability of the relative phase between quantum states, lies at the heart of quantum mechanics. Applications such as precision measurement, interferometry, and quantum computation are enabled by physical systems that have quantum states with robust coherence. With the creation of molecular ensembles at sub-$backslashmu$K temperatures, diatomic molecules have become a novel system under full quantum control. Here, we report on the observation of stable coherence between a pair of nuclear spin states of ultracold fermionic NaK molecules in the singlet rovibrational ground state. Employing microwave fields, we perform Ramsey spectroscopy and observe coherence times on the scale of one second. This work opens the door for the exploration of single molecules as a versatile quantum memory. Switchable long-range interactions between dipolar molecules can further enable two-qubit gates, allowing quantum storage and processing in the same physical system. Within the observed coherence time, $10^4$ one- and two-qubit gate operations will be feasible.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Coherence, the stability of the relative phase between quantum states, lies at the heart of quantum mechanics. Applications such as precision measurement, interferometry, and quantum computation are enabled by physical systems that have quantum states with robust coherence. With the creation of molecular ensembles at sub-$backslashmu$K temperatures, diatomic molecules have become a novel system under full quantum control. Here, we report on the observation of stable coherence between a pair of nuclear spin states of ultracold fermionic NaK molecules in the singlet rovibrational ground state. Employing microwave fields, we perform Ramsey spectroscopy and observe coherence times on the scale of one second. This work opens the door for the exploration of single molecules as a versatile quantum memory. Switchable long-range interactions between dipolar molecules can further enable two-qubit gates, allowing quantum storage and processing in the same physical system. Within the observed coherence time, $10^4$ one- and two-qubit gate operations will be feasible. |
Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W Homogeneous Atomic Fermi Gases Journal Article Physical Review Letters, 118 (12), 2017, ISSN: 10797114. @article{Mukherjee2017, title = {Homogeneous Atomic Fermi Gases}, author = {Biswaroop Mukherjee and Zhenjie Yan and Parth B Patel and Zoran Hadzibabic and Tarik Yefsah and Julian Struck and Martin W Zwierlein}, doi = {10.1103/PhysRevLett.118.123401}, issn = {10797114}, year = {2017}, date = {2017-01-01}, journal = {Physical Review Letters}, volume = {118}, number = {12}, abstract = {We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state. This directly confirms Pauli blocking in momentum space. For the spin-balanced unitary Fermi gas, we observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state. This directly confirms Pauli blocking in momentum space. For the spin-balanced unitary Fermi gas, we observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas. |
Fletcher, Richard J; Lopes, Raphael; Man, Jay; Navon, Nir; Smith, Robert P; Zwierlein, Martin W; Hadzibabic, Zoran Two- and three-body contacts in the unitary Bose gas Journal Article Science, 355 (6323), pp. 377–380, 2017, ISSN: 0036-8075. @article{Fletcher2017, title = {Two- and three-body contacts in the unitary Bose gas}, author = {Richard J Fletcher and Raphael Lopes and Jay Man and Nir Navon and Robert P Smith and Martin W Zwierlein and Zoran Hadzibabic}, url = {http://www.sciencemag.org/lookup/doi/10.1126/science.aai8195}, doi = {10.1126/science.aai8195}, issn = {0036-8075}, year = {2017}, date = {2017-01-01}, journal = {Science}, volume = {355}, number = {6323}, pages = {377--380}, abstract = {Tunable interactions make dilute atomic gases ideal for studying the collective dynamics of many-body systems. If the gas consists of strongly interacting fermions evenly divided into two groups of opposite spin, many of its properties can be distilled to two-body correlations. Fletcher et al. show that this does not hold for a gas of bosons, where identical particles happily congregate. The researchers measured a quantity that, in a thermal resonantly interacting Bose gas, depends only on three-body correlations. This enabled them to quantify the elusive correlations and establish unambiguously their effect on the physics of the many-body state.Science, this issue p. 377In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle correlations. This profound insight has transformed our understanding of strongly interacting Fermi gases. Using Ramsey interferometry, we studied coherent evolution of the resonantly interacting Bose gas, and we show here that it cannot be explained by only pairwise correlations. Our experiments reveal the crucial role of three-body correlations arising from Efimov physics and provide a direct measurement of the associated three-body contact.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Tunable interactions make dilute atomic gases ideal for studying the collective dynamics of many-body systems. If the gas consists of strongly interacting fermions evenly divided into two groups of opposite spin, many of its properties can be distilled to two-body correlations. Fletcher et al. show that this does not hold for a gas of bosons, where identical particles happily congregate. The researchers measured a quantity that, in a thermal resonantly interacting Bose gas, depends only on three-body correlations. This enabled them to quantify the elusive correlations and establish unambiguously their effect on the physics of the many-body state.Science, this issue p. 377In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle correlations. This profound insight has transformed our understanding of strongly interacting Fermi gases. Using Ramsey interferometry, we studied coherent evolution of the resonantly interacting Bose gas, and we show here that it cannot be explained by only pairwise correlations. Our experiments reveal the crucial role of three-body correlations arising from Efimov physics and provide a direct measurement of the associated three-body contact. |
2016 |
Cheuk, Lawrence W; Nichols, Matthew A; Lawrence, Katherine R; Okan, Melih; Zhang, Hao; Khatami, Ehsan; Trivedi, Nandini; Paiva, Thereza; Rigol, Marcos; Zwierlein, Martin W Observation of spatial charge and spin correlations in the 2D Fermi-Hubbard model Journal Article Science, 353 (6305), pp. 1260–1264, 2016, ISSN: 0036-8075. @article{Cheuk2016a, title = {Observation of spatial charge and spin correlations in the 2D Fermi-Hubbard model}, author = {Lawrence W Cheuk and Matthew A Nichols and Katherine R Lawrence and Melih Okan and Hao Zhang and Ehsan Khatami and Nandini Trivedi and Thereza Paiva and Marcos Rigol and Martin W Zwierlein}, url = {http://www.sciencemag.org/cgi/doi/10.1126/science.aag3349}, doi = {10.1126/science.aag3349}, issn = {0036-8075}, year = {2016}, date = {2016-09-01}, journal = {Science}, volume = {353}, number = {6305}, pages = {1260--1264}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Will, Sebastian A; Park, Jee Woo; Yan, Zoe Z; Loh, Huanqian; Zwierlein, Martin W Coherent Microwave Control of Ultracold 23Na40K Molecules Journal Article Physical Review Letters, 116 (22), pp. 225306, 2016, ISSN: 0031-9007. @article{Will2016, title = {Coherent Microwave Control of Ultracold 23Na40K Molecules}, author = {Sebastian A Will and Jee Woo Park and Zoe Z Yan and Huanqian Loh and Martin W Zwierlein}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.116.225306}, doi = {10.1103/PhysRevLett.116.225306}, issn = {0031-9007}, year = {2016}, date = {2016-06-01}, journal = {Physical Review Letters}, volume = {116}, number = {22}, pages = {225306}, abstract = {? 2016 American Physical Society.We demonstrate coherent microwave control of rotational and hyperfine states of trapped, ultracold, and chemically stable Na23K40 molecules. Starting with all molecules in the absolute rovibrational and hyperfine ground state, we study rotational transitions in combined magnetic and electric fields and explain the rich hyperfine structure. Following the transfer of the entire molecular ensemble into a single hyperfine level of the first rotationally excited state}, keywords = {}, pubstate = {published}, tppubtype = {article} } ? 2016 American Physical Society.We demonstrate coherent microwave control of rotational and hyperfine states of trapped, ultracold, and chemically stable Na23K40 molecules. Starting with all molecules in the absolute rovibrational and hyperfine ground state, we study rotational transitions in combined magnetic and electric fields and explain the rich hyperfine structure. Following the transfer of the entire molecular ensemble into a single hyperfine level of the first rotationally excited state |
Cheuk, Lawrence W; Nichols, Matthew A; Lawrence, Katherine R; Okan, Melih; Zhang, Hao; Zwierlein, Martin W Observation of 2D Fermionic Mott Insulators of 40K with Single-Site Resolution Journal Article Physical Review Letters, 116 (23), pp. 235301, 2016, ISSN: 0031-9007. @article{Cheuk2016, title = {Observation of 2D Fermionic Mott Insulators of 40K with Single-Site Resolution}, author = {Lawrence W Cheuk and Matthew A Nichols and Katherine R Lawrence and Melih Okan and Hao Zhang and Martin W Zwierlein}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.116.235301}, doi = {10.1103/PhysRevLett.116.235301}, issn = {0031-9007}, year = {2016}, date = {2016-06-01}, journal = {Physical Review Letters}, volume = {116}, number = {23}, pages = {235301}, abstract = {? 2016 American Physical Society.We report on the site-resolved observation of characteristic states of the two-dimensional repulsive Fermi-Hubbard model, using ultracold K40 atoms in an optical lattice. By varying the tunneling, interaction strength, and external confinement, we realize metallic, Mott-insulating, and band-insulating states. We directly measure the local moment, which quantifies the degree of on-site magnetization, as a function of temperature and chemical potential. Entropies per particle as low as 0.99(6)kB indicate that nearest-neighbor antiferromagnetic correlations should be detectable using spin-sensitive imaging.}, keywords = {}, pubstate = {published}, tppubtype = {article} } ? 2016 American Physical Society.We report on the site-resolved observation of characteristic states of the two-dimensional repulsive Fermi-Hubbard model, using ultracold K40 atoms in an optical lattice. By varying the tunneling, interaction strength, and external confinement, we realize metallic, Mott-insulating, and band-insulating states. We directly measure the local moment, which quantifies the degree of on-site magnetization, as a function of temperature and chemical potential. Entropies per particle as low as 0.99(6)kB indicate that nearest-neighbor antiferromagnetic correlations should be detectable using spin-sensitive imaging. |
Ku, Mark J H; Mukherjee, Biswaroop; Yefsah, Tarik; Zwierlein, Martin W Cascade of Solitonic Excitations in a Superfluid Fermi gas: From Planar Solitons to Vortex Rings and Lines Journal Article Physical Review Letters, 116 (4), pp. 045304, 2016, ISSN: 0031-9007. @article{Ku2016, title = {Cascade of Solitonic Excitations in a Superfluid Fermi gas: From Planar Solitons to Vortex Rings and Lines}, author = {Mark J H Ku and Biswaroop Mukherjee and Tarik Yefsah and Martin W Zwierlein}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.116.045304}, doi = {10.1103/PhysRevLett.116.045304}, issn = {0031-9007}, year = {2016}, date = {2016-01-01}, journal = {Physical Review Letters}, volume = {116}, number = {4}, pages = {045304}, abstract = {? 2016 American Physical Society.We follow the time evolution of a superfluid Fermi gas of resonantly interacting Li6 atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the ? soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium.}, keywords = {}, pubstate = {published}, tppubtype = {article} } ? 2016 American Physical Society.We follow the time evolution of a superfluid Fermi gas of resonantly interacting Li6 atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the ? soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium. |
Zwierlein, M W Thermodynamics of strongly interacting Fermi gases Inproceedings Proceedings of the International School of Physics "Enrico Fermi", 2016, ISSN: 18798195. @inproceedings{Zwierlein2016, title = {Thermodynamics of strongly interacting Fermi gases}, author = {M W Zwierlein}, doi = {10.3254/978-1-61499-694-1-143}, issn = {18798195}, year = {2016}, date = {2016-01-01}, booktitle = {Proceedings of the International School of Physics "Enrico Fermi"}, volume = {191}, abstract = {textcopyright Società Italiana di Fisica. These lecture notes review the universal thermodynamics of strongly interacting Fermi gases, experimentally realized with ultracold atoms near Feshbach resonances. These gases serve as a pristine model system for fermionic matter with contact interactions. Over the recent years, their equation of state has been measured to an ever-increasing precision that allows distinguishing between different theoretical approaches to the many-fermion problem. In the spin-balanced, resonant case, the equation of state only depends on temperature and density. The superfluid transition is signaled by a lambda-like feature in the specific heat of the gas. For non-resonant interactions, the scattering length introduces a conjugate extensive thermodynamic quantity, the contact. It encodes the probability to find two particles in close proximity and thus governs the interaction energy of the gas, the tails of the momentum distribution, the wings and the mean transition frequency of radiofrequency spectra, the probability of photoassociation and other experimental quantities. Introducing spin imbalance allows addressing a fifty year old question on the fate of fermionic superfluidity when there are more up spins than down spins and pairing cannot be complete. Phase separation between the superfluid and a mixed normal phase, as well as the eventual breakdown of superfluidity at the Pauli or Clogston-Chandrasekhar limit, have been directly observed. The mixed normal phase is identified as a Fermi liquid of Fermi polarons, dressed quasi-particles with a modified effective mass and energy. Prospects of observing an inhomogeneous superfluid state, the Fulde-Ferrell-Larkin-Ovchinnikov state of mobile Cooper pairs, are briefly discussed.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } textcopyright Società Italiana di Fisica. These lecture notes review the universal thermodynamics of strongly interacting Fermi gases, experimentally realized with ultracold atoms near Feshbach resonances. These gases serve as a pristine model system for fermionic matter with contact interactions. Over the recent years, their equation of state has been measured to an ever-increasing precision that allows distinguishing between different theoretical approaches to the many-fermion problem. In the spin-balanced, resonant case, the equation of state only depends on temperature and density. The superfluid transition is signaled by a lambda-like feature in the specific heat of the gas. For non-resonant interactions, the scattering length introduces a conjugate extensive thermodynamic quantity, the contact. It encodes the probability to find two particles in close proximity and thus governs the interaction energy of the gas, the tails of the momentum distribution, the wings and the mean transition frequency of radiofrequency spectra, the probability of photoassociation and other experimental quantities. Introducing spin imbalance allows addressing a fifty year old question on the fate of fermionic superfluidity when there are more up spins than down spins and pairing cannot be complete. Phase separation between the superfluid and a mixed normal phase, as well as the eventual breakdown of superfluidity at the Pauli or Clogston-Chandrasekhar limit, have been directly observed. The mixed normal phase is identified as a Fermi liquid of Fermi polarons, dressed quasi-particles with a modified effective mass and energy. Prospects of observing an inhomogeneous superfluid state, the Fulde-Ferrell-Larkin-Ovchinnikov state of mobile Cooper pairs, are briefly discussed. |
2015 |
Park, Jee Woo; Will, Sebastian A; Zwierlein, Martin W Two-photon pathway to ultracold ground state molecules of 23 Na 40 K Journal Article New Journal of Physics, 17 (7), pp. 075016, 2015, ISSN: 1367-2630. @article{Park2015a, title = {Two-photon pathway to ultracold ground state molecules of 23 Na 40 K}, author = {Jee Woo Park and Sebastian A Will and Martin W Zwierlein}, url = {http://stacks.iop.org/1367-2630/17/i=7/a=075016?key=crossref.eb17ad17bbe8e4c18015d414a37867d2}, doi = {10.1088/1367-2630/17/7/075016}, issn = {1367-2630}, year = {2015}, date = {2015-07-01}, journal = {New Journal of Physics}, volume = {17}, number = {7}, pages = {075016}, abstract = {? 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.We report on high-resolution spectroscopy of ultracold fermionic 23Na40K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B1? ? c3?+intermediate state. Photoassociation in a 23Na-40K atomic mixture and one-photon spectroscopy on 23Na40K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c3?+state. Two of these levels are found to be strongly perturbed by nearby B1? levels via spin-orbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex, or of resonantly mixed character in . The dominantly singlet level is used to locate the absolute rovibrational singlet ground state via Autler-Townes spectroscopy. We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state. Its binding energy is measured to be 5212.0447(1) cm-1, a thousand-fold improvement in accuracy compared to previous determinations. In their absolute singlet ground state, 23Na40K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye. Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.}, keywords = {}, pubstate = {published}, tppubtype = {article} } ? 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.We report on high-resolution spectroscopy of ultracold fermionic 23Na40K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B1? ? c3?+intermediate state. Photoassociation in a 23Na-40K atomic mixture and one-photon spectroscopy on 23Na40K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c3?+state. Two of these levels are found to be strongly perturbed by nearby B1? levels via spin-orbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex, or of resonantly mixed character in . The dominantly singlet level is used to locate the absolute rovibrational singlet ground state via Autler-Townes spectroscopy. We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state. Its binding energy is measured to be 5212.0447(1) cm-1, a thousand-fold improvement in accuracy compared to previous determinations. In their absolute singlet ground state, 23Na40K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye. Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules. |
Cheuk, Lawrence W; Nichols, Matthew A; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V; Bakr, Waseem S; Lompe, Thomas; Zwierlein, Martin W Quantum-Gas Microscope for Fermionic Atoms Journal Article Physical Review Letters, 114 (19), pp. 193001, 2015, ISSN: 0031-9007. @article{Cheuk2015, title = {Quantum-Gas Microscope for Fermionic Atoms}, author = {Lawrence W Cheuk and Matthew A Nichols and Melih Okan and Thomas Gersdorf and Vinay V Ramasesh and Waseem S Bakr and Thomas Lompe and Martin W Zwierlein}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.114.193001}, doi = {10.1103/PhysRevLett.114.193001}, issn = {0031-9007}, year = {2015}, date = {2015-05-01}, journal = {Physical Review Letters}, volume = {114}, number = {19}, pages = {193001}, abstract = {? 2015 American Physical Society.We realize a quantum-gas microscope for fermionic K40 atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement.}, keywords = {}, pubstate = {published}, tppubtype = {article} } ? 2015 American Physical Society.We realize a quantum-gas microscope for fermionic K40 atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. |
Zwierlein, M Ultracold atoms: How hot is the coldest matter? Journal Article Nature Physics, 11 (9), 2015, ISSN: 17452481 17452473. @article{Zwierlein2015, title = {Ultracold atoms: How hot is the coldest matter?}, author = {M Zwierlein}, doi = {10.1038/nphys3467}, issn = {17452481 17452473}, year = {2015}, date = {2015-01-01}, journal = {Nature Physics}, volume = {11}, number = {9}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Park, Jee Woo; Will, Sebastian A; Zwierlein, Martin W Ultracold Dipolar Gas of Fermionic 23Na40K Molecules in Their Absolute Ground State Journal Article Physical Review Letters, 114 (20), pp. 205302, 2015. @article{Park2015, title = {Ultracold Dipolar Gas of Fermionic 23Na40K Molecules in Their Absolute Ground State}, author = {Jee Woo Park and Sebastian A Will and Martin W Zwierlein}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.114.205302}, year = {2015}, date = {2015-01-01}, journal = {Physical Review Letters}, volume = {114}, number = {20}, pages = {205302}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2014 |
Ku, M J H; Ji, W; Mukherjee, B; Guardado-Sanchez, E; Cheuk, L W; Yefsah, T; Zwierlein, M W Motion of a solitonic vortex in the BEC-BCS crossover Journal Article Physical Review Letters, 113 (6), pp. 065301, 2014, ISSN: 10797114 00319007. @article{Ku2014, title = {Motion of a solitonic vortex in the BEC-BCS crossover}, author = {M J H Ku and W Ji and B Mukherjee and E Guardado-Sanchez and L W Cheuk and T Yefsah and M W Zwierlein}, doi = {10.1103/PhysRevLett.113.065301}, issn = {10797114 00319007}, year = {2014}, date = {2014-01-01}, journal = {Physical Review Letters}, volume = {113}, number = {6}, pages = {065301}, abstract = {We observe a long-lived solitary wave in a superfluid Fermi gas of Li6 atoms after phase imprinting. Tomographic imaging reveals the excitation to be a solitonic vortex, oriented transverse to the long axis of the cigar-shaped atom cloud. The precessional motion of the vortex is directly observed, and its period is measured as a function of the chemical potential in the BEC-BCS crossover. The long period and the correspondingly large ratio of the inertial to the bare mass of the vortex are in good agreement with estimates based on superfluid hydrodynamics that we derive here using the known equation of state in the BEC-BCS crossover. ? 2014 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We observe a long-lived solitary wave in a superfluid Fermi gas of Li6 atoms after phase imprinting. Tomographic imaging reveals the excitation to be a solitonic vortex, oriented transverse to the long axis of the cigar-shaped atom cloud. The precessional motion of the vortex is directly observed, and its period is measured as a function of the chemical potential in the BEC-BCS crossover. The long period and the correspondingly large ratio of the inertial to the bare mass of the vortex are in good agreement with estimates based on superfluid hydrodynamics that we derive here using the known equation of state in the BEC-BCS crossover. ? 2014 American Physical Society. |
Zwierlein, M W Superfluidity in ultracold atomic Fermi gases Incollection Bennemann, Karl-Heinz; Ketterson, John B (Ed.): Novel Superfluids, Vol. 2, Oxford University Press, Oxford, 2014. @incollection{Zwierlein2014, title = {Superfluidity in ultracold atomic Fermi gases}, author = {M W Zwierlein}, editor = {Karl-Heinz Bennemann and John B Ketterson}, year = {2014}, date = {2014-01-01}, booktitle = {Novel Superfluids, Vol. 2}, publisher = {Oxford University Press}, address = {Oxford}, chapter = {18}, keywords = {}, pubstate = {published}, tppubtype = {incollection} } |
2013 |
Tey, M K; Sidorenkov, L A; Guajardo, E R S; Grimm, R; Ku, M J H; Zwierlein, M W; Hou, Y -H; Pitaevskii, L; Stringari, S Collective modes in a unitary fermi gas across the superfluid phase transition Journal Article Physical Review Letters, 110 (5), 2013, ISSN: 00319007 10797114. @article{Tey2013, title = {Collective modes in a unitary fermi gas across the superfluid phase transition}, author = {M K Tey and L A Sidorenkov and E R S Guajardo and R Grimm and M J H Ku and M W Zwierlein and Y -H Hou and L Pitaevskii and S Stringari}, doi = {10.1103/PhysRevLett.110.055303}, issn = {00319007 10797114}, year = {2013}, date = {2013-01-01}, journal = {Physical Review Letters}, volume = {110}, number = {5}, abstract = {We provide a joint theoretical and experimental investigation of the temperature dependence of the collective oscillations of first sound nature exhibited by a highly elongated harmonically trapped Fermi gas at unitarity, including the region below the critical temperature for superfluidity. Differently from the lowest axial breathing mode, the hydrodynamic frequencies of the higher-nodal excitations show a temperature dependence, which is calculated starting from Landau two-fluid theory and using the available experimental knowledge of the equation of state. The experimental results agree with high accuracy with the predictions of theory and provide the first evidence for the temperature dependence of the collective frequencies near the superfluid phase transition. ? 2013 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We provide a joint theoretical and experimental investigation of the temperature dependence of the collective oscillations of first sound nature exhibited by a highly elongated harmonically trapped Fermi gas at unitarity, including the region below the critical temperature for superfluidity. Differently from the lowest axial breathing mode, the hydrodynamic frequencies of the higher-nodal excitations show a temperature dependence, which is calculated starting from Landau two-fluid theory and using the available experimental knowledge of the equation of state. The experimental results agree with high accuracy with the predictions of theory and provide the first evidence for the temperature dependence of the collective frequencies near the superfluid phase transition. ? 2013 American Physical Society. |
Yefsah, T; Sommer, A T; Ku, M J H; Cheuk, L W; Ji, W; Bakr, W S; Zwierlein, M W Heavy solitons in a fermionic superfluid Journal Article Nature, 499 (7459), 2013, ISSN: 00280836 14764687. @article{Yefsah2013, title = {Heavy solitons in a fermionic superfluid}, author = {T Yefsah and A T Sommer and M J H Ku and L W Cheuk and W Ji and W S Bakr and M W Zwierlein}, doi = {10.1038/nature12338}, issn = {00280836 14764687}, year = {2013}, date = {2013-01-01}, journal = {Nature}, volume = {499}, number = {7459}, abstract = {Solitons - solitary waves that maintain their shape as they propagate - occur as water waves in narrow canals, as light pulses in optical fibres and as quantum mechanical matter waves in superfluids and superconductors. Their highly nonlinear and localized nature makes them very sensitive probes of the medium in which they propagate. Here we create long-lived solitons in a strongly interacting superfluid of fermionic atoms and directly observe their motion. As the interactions are tuned from the regime of Bose-Einstein condensation of tightly bound molecules towards the Bardeen-Cooper-Schrieffer limit of long-range Cooper pairs, the solitons' effective mass increases markedly, to more than 200 times their bare mass, signalling strong quantum fluctuations. This mass enhancement is more than 50 times larger than the theoretically predicted value. Our work provides a benchmark for theories of non-equilibrium dynamics of strongly interacting fermions. ? 2013 Macmillan Publishers Limited. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Solitons - solitary waves that maintain their shape as they propagate - occur as water waves in narrow canals, as light pulses in optical fibres and as quantum mechanical matter waves in superfluids and superconductors. Their highly nonlinear and localized nature makes them very sensitive probes of the medium in which they propagate. Here we create long-lived solitons in a strongly interacting superfluid of fermionic atoms and directly observe their motion. As the interactions are tuned from the regime of Bose-Einstein condensation of tightly bound molecules towards the Bardeen-Cooper-Schrieffer limit of long-range Cooper pairs, the solitons' effective mass increases markedly, to more than 200 times their bare mass, signalling strong quantum fluctuations. This mass enhancement is more than 50 times larger than the theoretically predicted value. Our work provides a benchmark for theories of non-equilibrium dynamics of strongly interacting fermions. ? 2013 Macmillan Publishers Limited. All rights reserved. |
Zwierlein, M W Shock cooling a universe Journal Article Nature Physics, 9 (10), 2013, ISSN: 17452481 17452473. @article{Zwierlein2013, title = {Shock cooling a universe}, author = {M W Zwierlein}, doi = {10.1038/nphys2773}, issn = {17452481 17452473}, year = {2013}, date = {2013-01-01}, journal = {Nature Physics}, volume = {9}, number = {10}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Bakr, W; Cheuk, L W; Ku, M J -H; Park, J W; Sommer, A T; Will, S; Wu, C -H; Yefsah, T; Zwierlein, M W Strongly interacting Fermi gases Inproceedings EPJ Web of Conferences, 2013, ISSN: 21016275 2100014X. @inproceedings{Bakr2013, title = {Strongly interacting Fermi gases}, author = {W Bakr and L W Cheuk and M J -H Ku and J W Park and A T Sommer and S Will and C -H Wu and T Yefsah and M W Zwierlein}, doi = {10.1051/epjconf/20135701002}, issn = {21016275 2100014X}, year = {2013}, date = {2013-01-01}, booktitle = {EPJ Web of Conferences}, volume = {57}, abstract = {Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state. ? Owned by the authors, published by EDP Sciences, 2013.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state. ? Owned by the authors, published by EDP Sciences, 2013. |
2012 |
Sommer, A T; Cheuk, L W; Ku, M J H; Bakr, W S; Zwierlein, M W Evolution of fermion pairing from three to two dimensions Journal Article Physical Review Letters, 108 (4), 2012, ISSN: 00319007 10797114. @article{Sommer2012, title = {Evolution of fermion pairing from three to two dimensions}, author = {A T Sommer and L W Cheuk and M J H Ku and W S Bakr and M W Zwierlein}, doi = {10.1103/PhysRevLett.108.045302}, issn = {00319007 10797114}, year = {2012}, date = {2012-01-01}, journal = {Physical Review Letters}, volume = {108}, number = {4}, abstract = {We follow the evolution of fermion pairing in the dimensional crossover from three-dimensional to two-dimensional as a strongly interacting Fermi gas of Li6 atoms becomes confined to a stack of two-dimensional layers formed by a one-dimensional optical lattice. Decreasing the dimensionality leads to the opening of a gap in radio-frequency spectra, even on the Bardeen-Cooper- Schrieffer side of a Feshbach resonance. The measured binding energy of fermion pairs closely follows the theoretical two-body binding energy and, in the two-dimensional limit, the zero-temperature mean-field Bose-Einstein- condensation to Bardeen-Cooper-Schrieffer crossover theory. ? 2012 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We follow the evolution of fermion pairing in the dimensional crossover from three-dimensional to two-dimensional as a strongly interacting Fermi gas of Li6 atoms becomes confined to a stack of two-dimensional layers formed by a one-dimensional optical lattice. Decreasing the dimensionality leads to the opening of a gap in radio-frequency spectra, even on the Bardeen-Cooper- Schrieffer side of a Feshbach resonance. The measured binding energy of fermion pairs closely follows the theoretical two-body binding energy and, in the two-dimensional limit, the zero-temperature mean-field Bose-Einstein- condensation to Bardeen-Cooper-Schrieffer crossover theory. ? 2012 American Physical Society. |
Van Houcke, K; Werner, F; Kozik, E; Prokof'Ev, N; Svistunov, B; Ku, M J H; Sommer, A T; Cheuk, L W; Schirotzek, A; Zwierlein, M W Feynman diagrams versus Fermi-gas Feynman emulator Journal Article Nature Physics, 8 (5), 2012, ISSN: 17452473 17452481. @article{VanHoucke2012, title = {Feynman diagrams versus Fermi-gas Feynman emulator}, author = {K {Van Houcke} and F Werner and E Kozik and N Prokof'Ev and B Svistunov and M J H Ku and A T Sommer and L W Cheuk and A Schirotzek and M W Zwierlein}, doi = {10.1038/nphys2273}, issn = {17452473 17452481}, year = {2012}, date = {2012-01-01}, journal = {Nature Physics}, volume = {8}, number = {5}, abstract = {Precise understanding of strongly interacting fermions, from electrons in modern materials to nuclear matter, presents a major goal in modern physics. However, the theoretical description of interacting Fermi systems is usually plagued by the intricate quantum statistics at play. Here we present a cross-validation between a new theoretical approach, bold diagrammatic Monte Carlo 1-3, and precision experiments on ultracold atoms. Specifically, we compute and measure, with unprecedented precision, the normal-state equation of state of the unitary gas, a prototypical example of a strongly correlated fermionic system 4-6. Excellent agreement demonstrates that a series of Feynman diagrams can be controllably resummed in a non-perturbative regime using bold diagrammatic Monte Carlo. ? 2012 Macmillan Publishers Limited. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Precise understanding of strongly interacting fermions, from electrons in modern materials to nuclear matter, presents a major goal in modern physics. However, the theoretical description of interacting Fermi systems is usually plagued by the intricate quantum statistics at play. Here we present a cross-validation between a new theoretical approach, bold diagrammatic Monte Carlo 1-3, and precision experiments on ultracold atoms. Specifically, we compute and measure, with unprecedented precision, the normal-state equation of state of the unitary gas, a prototypical example of a strongly correlated fermionic system 4-6. Excellent agreement demonstrates that a series of Feynman diagrams can be controllably resummed in a non-perturbative regime using bold diagrammatic Monte Carlo. ? 2012 Macmillan Publishers Limited. All rights reserved. |
Park, J W; Wu, C -H; Santiago, I; Tiecke, T G; Will, S; Ahmadi, P; Zwierlein, M W Quantum degenerate Bose-Fermi mixture of chemically different atomic species with widely tunable interactions Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 85 (5), 2012, ISSN: 10502947 10941622. @article{Park2012, title = {Quantum degenerate Bose-Fermi mixture of chemically different atomic species with widely tunable interactions}, author = {J W Park and C -H Wu and I Santiago and T G Tiecke and S Will and P Ahmadi and M W Zwierlein}, doi = {10.1103/PhysRevA.85.051602}, issn = {10502947 10941622}, year = {2012}, date = {2012-01-01}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, volume = {85}, number = {5}, abstract = {We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with widely tunable interactions via broad interspecies Feshbach resonances. Over 30 Feshbach resonances between 23Na and 40K were identified, including p-wave multiplet resonances. The large and negative triplet background scattering length between 23Na and 40K causes a sharp enhancement of the fermion density in the presence of a Bose condensate. As explained via the asymptotic bound-state model, this strong background scattering leads to wide Feshbach resonances observed at low magnetic fields. Our work opens up the prospect to create chemically stable, fermionic ground-state molecules of 23Na-40K, where strong, long-range dipolar interactions would set the dominant energy scale. ? 2012 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with widely tunable interactions via broad interspecies Feshbach resonances. Over 30 Feshbach resonances between 23Na and 40K were identified, including p-wave multiplet resonances. The large and negative triplet background scattering length between 23Na and 40K causes a sharp enhancement of the fermion density in the presence of a Bose condensate. As explained via the asymptotic bound-state model, this strong background scattering leads to wide Feshbach resonances observed at low magnetic fields. Our work opens up the prospect to create chemically stable, fermionic ground-state molecules of 23Na-40K, where strong, long-range dipolar interactions would set the dominant energy scale. ? 2012 American Physical Society. |
Ku, M J H; Sommer, A T; Cheuk, L W; Zwierlein, M W Revealing the superfluid lambda transition in the universal thermodynamics of a unitary fermi gas Journal Article Science, 335 (6068), 2012, ISSN: 10959203 00368075. @article{Ku2012, title = {Revealing the superfluid lambda transition in the universal thermodynamics of a unitary fermi gas}, author = {M J H Ku and A T Sommer and L W Cheuk and M W Zwierlein}, doi = {10.1126/science.1214987}, issn = {10959203 00368075}, year = {2012}, date = {2012-01-01}, journal = {Science}, volume = {335}, number = {6068}, abstract = {Fermi gases, collections of fermions such as neutrons and electrons, are found throughout nature, from solids to neutron stars. Interacting Fermi gases can form a superfluid or, for charged fermions, a superconductor. We have observed the superfluid phase transition in a strongly interacting Fermi gas by high-precision measurements of the local compressibility, density, and pressure. Our data completely determine the universal thermodynamics of these gases without any fit or external thermometer. The onset of superfluidity is observed in the compressibility, the chemical potential, the entropy, and the heat capacity, which displays a characteristic lambda-like feature at the critical temperature Tc/TF = 0.167(13). The ground-state energy is 3/5 ?N EF with ? = 0.376(4). Our measurements provide a benchmark for many-body theories of strongly interacting fermions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Fermi gases, collections of fermions such as neutrons and electrons, are found throughout nature, from solids to neutron stars. Interacting Fermi gases can form a superfluid or, for charged fermions, a superconductor. We have observed the superfluid phase transition in a strongly interacting Fermi gas by high-precision measurements of the local compressibility, density, and pressure. Our data completely determine the universal thermodynamics of these gases without any fit or external thermometer. The onset of superfluidity is observed in the compressibility, the chemical potential, the entropy, and the heat capacity, which displays a characteristic lambda-like feature at the critical temperature Tc/TF = 0.167(13). The ground-state energy is 3/5 ?N EF with ? = 0.376(4). Our measurements provide a benchmark for many-body theories of strongly interacting fermions. |
Cheuk, L W; Sommer, A T; Hadzibabic, Z; Yefsah, T; Bakr, W S; Zwierlein, M W Spin-injection spectroscopy of a spin-orbit coupled Fermi gas Journal Article Physical Review Letters, 109 (9), 2012, ISSN: 00319007 10797114. @article{Cheuk2012, title = {Spin-injection spectroscopy of a spin-orbit coupled Fermi gas}, author = {L W Cheuk and A T Sommer and Z Hadzibabic and T Yefsah and W S Bakr and M W Zwierlein}, doi = {10.1103/PhysRevLett.109.095302}, issn = {00319007 10797114}, year = {2012}, date = {2012-01-01}, journal = {Physical Review Letters}, volume = {109}, number = {9}, abstract = {The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum degenerate matter. We directly reveal the spin-orbit gap via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. We also create a spin-orbit coupled lattice and probe its spinful band structure, which features additional spin gaps and a fully gapped spectrum. In the presence of s-wave interactions, such systems should display induced p-wave pairing, topological superfluidity, and Majorana edge states. ? 2012 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum degenerate matter. We directly reveal the spin-orbit gap via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. We also create a spin-orbit coupled lattice and probe its spinful band structure, which features additional spin gaps and a fully gapped spectrum. In the presence of s-wave interactions, such systems should display induced p-wave pairing, topological superfluidity, and Majorana edge states. ? 2012 American Physical Society. |
Wu, C -H; Park, J W; Ahmadi, P; Will, S; Zwierlein, M W Ultracold fermionic Feshbach molecules of Na23K40 Journal Article Physical Review Letters, 109 (8), 2012, ISSN: 00319007 10797114. @article{Wu2012, title = {Ultracold fermionic Feshbach molecules of Na23K40}, author = {C -H Wu and J W Park and P Ahmadi and S Will and M W Zwierlein}, doi = {10.1103/PhysRevLett.109.085301}, issn = {00319007 10797114}, year = {2012}, date = {2012-01-01}, journal = {Physical Review Letters}, volume = {109}, number = {8}, abstract = {We report on the formation of ultracold weakly bound Feshbach molecules of Na23K40, the first fermionic molecule that is chemically stable in its absolute ground state. The lifetime of the nearly degenerate molecular gas exceeds 100ms in the vicinity of the Feshbach resonance. The measured dependence of the molecular binding energy on the magnetic field demonstrates the open-channel character of the molecules over a wide field range and implies significant singlet admixture. This will enable efficient transfer into the singlet vibrational ground state, resulting in a stable molecular Fermi gas with strong dipolar interactions. ? 2012 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report on the formation of ultracold weakly bound Feshbach molecules of Na23K40, the first fermionic molecule that is chemically stable in its absolute ground state. The lifetime of the nearly degenerate molecular gas exceeds 100ms in the vicinity of the Feshbach resonance. The measured dependence of the molecular binding energy on the magnetic field demonstrates the open-channel character of the molecules over a wide field range and implies significant singlet admixture. This will enable efficient transfer into the singlet vibrational ground state, resulting in a stable molecular Fermi gas with strong dipolar interactions. ? 2012 American Physical Society. |
2011 |
Vernier, E; Pekker, D; Zwierlein, M W; Demler, E Bound states of a localized magnetic impurity in a superfluid of paired ultracold fermions Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 83 (3), 2011, ISSN: 10502947 10941622. @article{Vernier2011, title = {Bound states of a localized magnetic impurity in a superfluid of paired ultracold fermions}, author = {E Vernier and D Pekker and M W Zwierlein and E Demler}, doi = {10.1103/PhysRevA.83.033619}, issn = {10502947 10941622}, year = {2011}, date = {2011-01-01}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, volume = {83}, number = {3}, abstract = {We consider a localized impurity atom that interacts with a cloud of fermions in the paired state. We develop an effective scattering length description of the interaction between an impurity and a fermionic atom using their vacuum scattering length. Treating the pairing of fermions at the mean-field level, we show that the impurity atom acts like a magnetic impurity in the condensed matter context, and leads to the formation of a pair of Shiba bound states inside the superconducting gap. In addition, the impurity atom can lead to the formation of deeply bound states below the Fermi sea. ? 2011 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We consider a localized impurity atom that interacts with a cloud of fermions in the paired state. We develop an effective scattering length description of the interaction between an impurity and a fermionic atom using their vacuum scattering length. Treating the pairing of fermions at the mean-field level, we show that the impurity atom acts like a magnetic impurity in the condensed matter context, and leads to the formation of a pair of Shiba bound states inside the superconducting gap. In addition, the impurity atom can lead to the formation of deeply bound states below the Fermi sea. ? 2011 American Physical Society. |
Pekker, D; Babadi, M; Sensarma, R; Zinner, N; Pollet, L; Zwierlein, M W; Demler, E Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances Journal Article Physical Review Letters, 106 (5), 2011, ISSN: 00319007 10797114. @article{Pekker2011, title = {Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances}, author = {D Pekker and M Babadi and R Sensarma and N Zinner and L Pollet and M W Zwierlein and E Demler}, doi = {10.1103/PhysRevLett.106.050402}, issn = {00319007 10797114}, year = {2011}, date = {2011-01-01}, journal = {Physical Review Letters}, volume = {106}, number = {5}, abstract = {We study the quench dynamics of a two-component ultracold Fermi gas from the weak into the strong interaction regime, where the short time dynamics are governed by the exponential growth rate of unstable collective modes. We obtain an effective interaction that takes into account both Pauli blocking and the energy dependence of the scattering amplitude near a Feshbach resonance. Using this interaction we analyze the competing instabilities towards Stoner ferromagnetism and pairing. ? 2011 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the quench dynamics of a two-component ultracold Fermi gas from the weak into the strong interaction regime, where the short time dynamics are governed by the exponential growth rate of unstable collective modes. We obtain an effective interaction that takes into account both Pauli blocking and the energy dependence of the scattering amplitude near a Feshbach resonance. Using this interaction we analyze the competing instabilities towards Stoner ferromagnetism and pairing. ? 2011 American Physical Society. |
Sommer, A; Ku, M; Zwierlein, M W Spin transport in polaronic and superfluid Fermi gases Journal Article New Journal of Physics, 13 , 2011, ISSN: 13672630. @article{Sommer2011a, title = {Spin transport in polaronic and superfluid Fermi gases}, author = {A Sommer and M Ku and M W Zwierlein}, doi = {10.1088/1367-2630/13/5/055009}, issn = {13672630}, year = {2011}, date = {2011-01-01}, journal = {New Journal of Physics}, volume = {13}, abstract = {We present measurements of spin transport in ultracold gases of fermionic 6Li in a mixture of two spin states at a Feshbach resonance. In particular, we study the spin-dipole mode, where the two spin components are displaced from each other against a harmonic restoring force. We prepare a highly imbalanced, or polaronic, spin mixture with a spin-dipole excitation and we observe strong, unitarity-limited damping of the spin-dipole mode. In gases with small spin imbalance, below the Pauli limit for superfluidity, we observe strongly damped spin flow even in the presence of a superfluid core. This indicates strong mutual friction between superfluid and polarized normal spins, possibly involving Andreev reflection at the superfluid-normal interface. ? IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present measurements of spin transport in ultracold gases of fermionic 6Li in a mixture of two spin states at a Feshbach resonance. In particular, we study the spin-dipole mode, where the two spin components are displaced from each other against a harmonic restoring force. We prepare a highly imbalanced, or polaronic, spin mixture with a spin-dipole excitation and we observe strong, unitarity-limited damping of the spin-dipole mode. In gases with small spin imbalance, below the Pauli limit for superfluidity, we observe strongly damped spin flow even in the presence of a superfluid core. This indicates strong mutual friction between superfluid and polarized normal spins, possibly involving Andreev reflection at the superfluid-normal interface. ? IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. |
Wu, C -H; Santiago, I; Park, J W; Ahmadi, P; Zwierlein, M W Strongly interacting isotopic Bose-Fermi mixture immersed in a Fermi sea Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 84 (1), 2011, ISSN: 10502947 10941622. @article{Wu2011, title = {Strongly interacting isotopic Bose-Fermi mixture immersed in a Fermi sea}, author = {C -H Wu and I Santiago and J W Park and P Ahmadi and M W Zwierlein}, doi = {10.1103/PhysRevA.84.011601}, issn = {10502947 10941622}, year = {2011}, date = {2011-01-01}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, volume = {84}, number = {1}, abstract = {We have created a triply quantum-degenerate mixture of bosonic K41 and two fermionic species K40 and Li6. The boson is shown to be an efficient coolant for the two fermions, spurring hopes for the observation of fermionic superfluids with imbalanced masses. We observe multiple heteronuclear Feshbach resonances, in particular a wide s-wave resonance for the combination K41-K40, opening up studies of strongly interacting isotopic Bose-Fermi mixtures. For large imbalance in the local densities of different species, we enter the polaronic regime of dressed impurities immersed in a bosonic or fermionic bath. ? 2011 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We have created a triply quantum-degenerate mixture of bosonic K41 and two fermionic species K40 and Li6. The boson is shown to be an efficient coolant for the two fermions, spurring hopes for the observation of fermionic superfluids with imbalanced masses. We observe multiple heteronuclear Feshbach resonances, in particular a wide s-wave resonance for the combination K41-K40, opening up studies of strongly interacting isotopic Bose-Fermi mixtures. For large imbalance in the local densities of different species, we enter the polaronic regime of dressed impurities immersed in a bosonic or fermionic bath. ? 2011 American Physical Society. |
Sommer, A; Ku, M; Roati, G; Zwierlein, M W Universal spin transport in a strongly interacting Fermi gas Journal Article Nature, 472 (7342), 2011, ISSN: 00280836 14764687. @article{Sommer2011, title = {Universal spin transport in a strongly interacting Fermi gas}, author = {A Sommer and M Ku and G Roati and M W Zwierlein}, doi = {10.1038/nature09989}, issn = {00280836 14764687}, year = {2011}, date = {2011-01-01}, journal = {Nature}, volume = {472}, number = {7342}, abstract = {Transport of fermions, particles with half-integer spin, is central to many fields of physics. Electron transport runs modern technology, defining states of matter such as superconductors and insulators, and electron spin is being explored as a new carrier of information. Neutrino transport energizes supernova explosions following the collapse of a dying star, and hydrodynamic transport of the quark-gluon plasma governed the expansion of the early Universe. However, our understanding of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold gases of fermionic atoms realize a pristine model for such systems and can be studied in real time with the precision of atomic physics. Even above the superfluid transition, such gases flow as an almost perfect fluid with very low viscosity when interactions are tuned to a scattering resonance. In this hydrodynamic regime, collective density excitations are weakly damped. Here we experimentally investigate spin excitations in a Fermi gas of 6 Li atoms, finding that, in contrast, they are maximally damped. A spin current is induced by spatially separating two spin components and observing their evolution in an external trapping potential. We demonstrate that interactions can be strong enough to reverse spin currents, with components of opposite spin reflecting off each other. Near equilibrium, we obtain the spin drag coefficient, the spin diffusivity and the spin susceptibility as a function of temperature on resonance and show that they obey universal laws at high temperatures. In the degenerate regime, the spin diffusivity approaches a value set by [planck]/m, the quantum limit of diffusion, where [planck]/m is Plancks constant divided by and m the atomic mass. For repulsive interactions, our measurements seem to exclude a metastable ferromagnetic state. ? 2011 Macmillan Publishers Limited. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Transport of fermions, particles with half-integer spin, is central to many fields of physics. Electron transport runs modern technology, defining states of matter such as superconductors and insulators, and electron spin is being explored as a new carrier of information. Neutrino transport energizes supernova explosions following the collapse of a dying star, and hydrodynamic transport of the quark-gluon plasma governed the expansion of the early Universe. However, our understanding of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold gases of fermionic atoms realize a pristine model for such systems and can be studied in real time with the precision of atomic physics. Even above the superfluid transition, such gases flow as an almost perfect fluid with very low viscosity when interactions are tuned to a scattering resonance. In this hydrodynamic regime, collective density excitations are weakly damped. Here we experimentally investigate spin excitations in a Fermi gas of 6 Li atoms, finding that, in contrast, they are maximally damped. A spin current is induced by spatially separating two spin components and observing their evolution in an external trapping potential. We demonstrate that interactions can be strong enough to reverse spin currents, with components of opposite spin reflecting off each other. Near equilibrium, we obtain the spin drag coefficient, the spin diffusivity and the spin susceptibility as a function of temperature on resonance and show that they obey universal laws at high temperatures. In the degenerate regime, the spin diffusivity approaches a value set by [planck]/m, the quantum limit of diffusion, where [planck]/m is Plancks constant divided by and m the atomic mass. For repulsive interactions, our measurements seem to exclude a metastable ferromagnetic state. ? 2011 Macmillan Publishers Limited. All rights reserved. |
2009 |
Zwierlein, M Atomic physics: Neutral atoms put in charge Journal Article Nature, 462 (7273), 2009, ISSN: 00280836 14764687. @article{Zwierlein2009a, title = {Atomic physics: Neutral atoms put in charge}, author = {M Zwierlein}, doi = {10.1038/462584a}, issn = {00280836 14764687}, year = {2009}, date = {2009-01-01}, journal = {Nature}, volume = {462}, number = {7273}, abstract = {An elegant experiment shows that atoms subjected to a pair of laser beams can behave like electrons in a magnetic field, as demonstrated by the appearance of quantized vortices in a neutral superfluid. ? 2009 Macmillan Publishers Limited. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An elegant experiment shows that atoms subjected to a pair of laser beams can behave like electrons in a magnetic field, as demonstrated by the appearance of quantized vortices in a neutral superfluid. ? 2009 Macmillan Publishers Limited. All rights reserved. |
Zwierlein, M W Fermionic superfluidity and the BEC-BCS crossover in ultracold atomic Fermi gases Inproceedings Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology, ISQM-Tokyo 2008, 2009, ISBN: 981428212X | 9789814282123. @inproceedings{Zwierlein2009b, title = {Fermionic superfluidity and the BEC-BCS crossover in ultracold atomic Fermi gases}, author = {M W Zwierlein}, isbn = {981428212X | 9789814282123}, year = {2009}, date = {2009-01-01}, booktitle = {Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology, ISQM-Tokyo 2008}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } |
Schirotzek, A; Wu, C -H; Sommer, A; Zwierlein, M W Observation of Fermi polarons in a tunable Fermi liquid of ultracold atoms Journal Article Physical Review Letters, 102 (23), 2009, ISSN: 00319007 10797114. @article{Schirotzek2009, title = {Observation of Fermi polarons in a tunable Fermi liquid of ultracold atoms}, author = {A Schirotzek and C -H Wu and A Sommer and M W Zwierlein}, doi = {10.1103/PhysRevLett.102.230402}, issn = {00319007 10797114}, year = {2009}, date = {2009-01-01}, journal = {Physical Review Letters}, volume = {102}, number = {23}, abstract = {We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities' rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for various interaction strengths around a Feshbach resonance. At a critical interaction, we observe the transition from polaronic to molecular binding. Here, the imbalanced Fermi liquid undergoes a phase transition into a Bose liquid, coexisting with a Fermi sea. ? 2009 The American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities' rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for various interaction strengths around a Feshbach resonance. At a critical interaction, we observe the transition from polaronic to molecular binding. Here, the imbalanced Fermi liquid undergoes a phase transition into a Bose liquid, coexisting with a Fermi sea. ? 2009 The American Physical Society. |
2008 |
Zwierlein, M W Fermionic Superfluidity and the BEC-BCS Crossover in Ultracold Atomic Fermi Gases Inproceedings Ishioka, Sachio; Fujikawa, Kazuo (Ed.): Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology - ISQM Tokyo 2008, World Scientific, Tokyo, Japan, 2008. @inproceedings{Zwierlein2008, title = {Fermionic Superfluidity and the BEC-BCS Crossover in Ultracold Atomic Fermi Gases}, author = {M W Zwierlein}, editor = {Sachio Ishioka and Kazuo Fujikawa}, year = {2008}, date = {2008-01-01}, booktitle = {Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology - ISQM Tokyo 2008}, publisher = {World Scientific}, address = {Tokyo, Japan}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } |
Ketterle, W; Zwierlein, M W Making, probing and understanding ultracold Fermi gases Inproceedings Proceedings of the International School of Physics "Enrico Fermi", 2008, ISSN: 0074784X 18798195. @inproceedings{Ketterle2007, title = {Making, probing and understanding ultracold Fermi gases}, author = {W Ketterle and M W Zwierlein}, doi = {10.3254/978-1-58603-846-5-95}, issn = {0074784X 18798195}, year = {2008}, date = {2008-01-01}, booktitle = {Proceedings of the International School of Physics "Enrico Fermi"}, volume = {164}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } |
2007 |
Baym, G; Pethick, C J; Yu, Z; Zwierlein, M W Coherence and clock shifts in ultracold fermi gases with resonant interactions Journal Article Physical Review Letters, 99 (19), 2007, ISSN: 00319007 10797114. @article{Baym2007, title = {Coherence and clock shifts in ultracold fermi gases with resonant interactions}, author = {G Baym and C J Pethick and Z Yu and M W Zwierlein}, doi = {10.1103/PhysRevLett.99.190407}, issn = {00319007 10797114}, year = {2007}, date = {2007-01-01}, journal = {Physical Review Letters}, volume = {99}, number = {19}, abstract = {Using arguments based on sum rules, we derive a general result for the average shifts of rf lines in Fermi gases in terms of interatomic interaction strengths and two-particle correlation functions. We show that near an interaction resonance shifts vary inversely with the atomic scattering length, rather than linearly as in dilute gases, thus accounting for the experimental observation that clock shifts remain finite at Feshbach resonances. ? 2007 The American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using arguments based on sum rules, we derive a general result for the average shifts of rf lines in Fermi gases in terms of interatomic interaction strengths and two-particle correlation functions. We show that near an interaction resonance shifts vary inversely with the atomic scattering length, rather than linearly as in dilute gases, thus accounting for the experimental observation that clock shifts remain finite at Feshbach resonances. ? 2007 The American Physical Society. |
Schunck, C H; Shin, Y; Schirotzek, A; Zwierlein, M W; Ketterle, W Pairing without superfluidity: The ground state of an imbalanced fermi mixture Journal Article Science, 316 (5826), 2007, ISSN: 00368075 10959203. @article{Schunck2007a, title = {Pairing without superfluidity: The ground state of an imbalanced fermi mixture}, author = {C H Schunck and Y Shin and A Schirotzek and M W Zwierlein and W Ketterle}, doi = {10.1126/science.1140749}, issn = {00368075 10959203}, year = {2007}, date = {2007-01-01}, journal = {Science}, volume = {316}, number = {5826}, abstract = {We used radio-frequency spectroscopy to study pairing in the normal and superfluid phases of a strongly interacting Fermi gas with imbalanced spin populations. At high spin imbalances, the system does not become superfluid even at zero temperature. In this normal phase, full pairing of the minority atoms was observed. Hence, mismatched Fermi surfaces do not prevent pairing but can quench the superfluid state, thus realizing a system of fermion pairs that do not condense even at the lowest temperature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We used radio-frequency spectroscopy to study pairing in the normal and superfluid phases of a strongly interacting Fermi gas with imbalanced spin populations. At high spin imbalances, the system does not become superfluid even at zero temperature. In this normal phase, full pairing of the minority atoms was observed. Hence, mismatched Fermi surfaces do not prevent pairing but can quench the superfluid state, thus realizing a system of fermion pairs that do not condense even at the lowest temperature. |
Schunck, C H; Zwierlein, M W; Schirotzek, A; Ketterle, W Superfluid Expansion of a Rotating Fermi Gas Journal Article Physical Review Letters, 98 (5), pp. 50404, 2007. @article{Schunck2007, title = {Superfluid Expansion of a Rotating Fermi Gas}, author = {C H Schunck and M W Zwierlein and A Schirotzek and W Ketterle}, year = {2007}, date = {2007-01-01}, journal = {Physical Review Letters}, volume = {98}, number = {5}, pages = {50404}, publisher = {APS}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2020 |
Measuring total density correlations in a Fermi-Hubbard gas via bilayer microscopy Journal Article preprint arXiv:2003.11669, 2020. |
Resonant dipolar collisions of ultracold molecules induced by microwave dressing Journal Article preprint arXiv:2003.02830, 2020. |
2019 |
Quantum Simulators: Architectures and Opportunities Journal Article preprint arXiv:1912.06938, 2019. |
Geometric squeezing into the lowest Landau level Journal Article preprint arXiv:1911.12347, 2019. |
Universal Sound Diffusion in a Strongly Interacting Fermi Gas Journal Article preprint arXiv:1909.02555, 2019. |
Photoinduced Two-Body Loss of Ultracold Molecules Journal Article Physical Review Letters, 123 (12), 2019, ISSN: 10797114. |
Spectral Response and Contact of the Unitary Fermi Gas Journal Article Physical Review Letters, 122 (20), pp. 203402, 2019. |
Bose polarons near quantum criticality Journal Article preprint arXiv:1904.02685, 2019. |
Boiling a Unitary Fermi Liquid Journal Article Physical Review Letters, 122 (9), 2019, ISSN: 10797114. |
Spin transport in a Mott insulator of ultracold fermions Journal Article Science, 363 (6425), pp. 383–387, 2019, ISSN: 10959203. |
2018 |
Photoassociation of ultracold NaLi Journal Article Physical Chemistry Chemical Physics, 20 (7), 2018, ISSN: 14639076. |
Two-photon spectroscopy of the NaLi triplet ground state Journal Article Physical Chemistry Chemical Physics, 20 (7), 2018, ISSN: 14639076. |
2017 |
Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments Journal Article Physical Review Letters, 119 (14), pp. 143001, 2017, ISSN: 0031-9007. |
Second-scale nuclear spin coherence time of ultracold 23 Na 40 K molecules Journal Article Science, 357 (6349), pp. 372–375, 2017, ISSN: 0036-8075. |
Homogeneous Atomic Fermi Gases Journal Article Physical Review Letters, 118 (12), 2017, ISSN: 10797114. |
Two- and three-body contacts in the unitary Bose gas Journal Article Science, 355 (6323), pp. 377–380, 2017, ISSN: 0036-8075. |
2016 |
Observation of spatial charge and spin correlations in the 2D Fermi-Hubbard model Journal Article Science, 353 (6305), pp. 1260–1264, 2016, ISSN: 0036-8075. |
Coherent Microwave Control of Ultracold 23Na40K Molecules Journal Article Physical Review Letters, 116 (22), pp. 225306, 2016, ISSN: 0031-9007. |
Observation of 2D Fermionic Mott Insulators of 40K with Single-Site Resolution Journal Article Physical Review Letters, 116 (23), pp. 235301, 2016, ISSN: 0031-9007. |
Cascade of Solitonic Excitations in a Superfluid Fermi gas: From Planar Solitons to Vortex Rings and Lines Journal Article Physical Review Letters, 116 (4), pp. 045304, 2016, ISSN: 0031-9007. |
Thermodynamics of strongly interacting Fermi gases Inproceedings Proceedings of the International School of Physics "Enrico Fermi", 2016, ISSN: 18798195. |
2015 |
Two-photon pathway to ultracold ground state molecules of 23 Na 40 K Journal Article New Journal of Physics, 17 (7), pp. 075016, 2015, ISSN: 1367-2630. |
Quantum-Gas Microscope for Fermionic Atoms Journal Article Physical Review Letters, 114 (19), pp. 193001, 2015, ISSN: 0031-9007. |
Ultracold atoms: How hot is the coldest matter? Journal Article Nature Physics, 11 (9), 2015, ISSN: 17452481 17452473. |
Ultracold Dipolar Gas of Fermionic 23Na40K Molecules in Their Absolute Ground State Journal Article Physical Review Letters, 114 (20), pp. 205302, 2015. |
2014 |
Motion of a solitonic vortex in the BEC-BCS crossover Journal Article Physical Review Letters, 113 (6), pp. 065301, 2014, ISSN: 10797114 00319007. |
Superfluidity in ultracold atomic Fermi gases Incollection Bennemann, Karl-Heinz; Ketterson, John B (Ed.): Novel Superfluids, Vol. 2, Oxford University Press, Oxford, 2014. |
2013 |
Collective modes in a unitary fermi gas across the superfluid phase transition Journal Article Physical Review Letters, 110 (5), 2013, ISSN: 00319007 10797114. |
Heavy solitons in a fermionic superfluid Journal Article Nature, 499 (7459), 2013, ISSN: 00280836 14764687. |
Shock cooling a universe Journal Article Nature Physics, 9 (10), 2013, ISSN: 17452481 17452473. |
Strongly interacting Fermi gases Inproceedings EPJ Web of Conferences, 2013, ISSN: 21016275 2100014X. |
2012 |
Evolution of fermion pairing from three to two dimensions Journal Article Physical Review Letters, 108 (4), 2012, ISSN: 00319007 10797114. |
Feynman diagrams versus Fermi-gas Feynman emulator Journal Article Nature Physics, 8 (5), 2012, ISSN: 17452473 17452481. |
Quantum degenerate Bose-Fermi mixture of chemically different atomic species with widely tunable interactions Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 85 (5), 2012, ISSN: 10502947 10941622. |
Revealing the superfluid lambda transition in the universal thermodynamics of a unitary fermi gas Journal Article Science, 335 (6068), 2012, ISSN: 10959203 00368075. |
Spin-injection spectroscopy of a spin-orbit coupled Fermi gas Journal Article Physical Review Letters, 109 (9), 2012, ISSN: 00319007 10797114. |
Ultracold fermionic Feshbach molecules of Na23K40 Journal Article Physical Review Letters, 109 (8), 2012, ISSN: 00319007 10797114. |
2011 |
Bound states of a localized magnetic impurity in a superfluid of paired ultracold fermions Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 83 (3), 2011, ISSN: 10502947 10941622. |
Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances Journal Article Physical Review Letters, 106 (5), 2011, ISSN: 00319007 10797114. |
Spin transport in polaronic and superfluid Fermi gases Journal Article New Journal of Physics, 13 , 2011, ISSN: 13672630. |
Strongly interacting isotopic Bose-Fermi mixture immersed in a Fermi sea Journal Article Physical Review A - Atomic, Molecular, and Optical Physics, 84 (1), 2011, ISSN: 10502947 10941622. |
Universal spin transport in a strongly interacting Fermi gas Journal Article Nature, 472 (7342), 2011, ISSN: 00280836 14764687. |
2009 |
Atomic physics: Neutral atoms put in charge Journal Article Nature, 462 (7273), 2009, ISSN: 00280836 14764687. |
Fermionic superfluidity and the BEC-BCS crossover in ultracold atomic Fermi gases Inproceedings Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology, ISQM-Tokyo 2008, 2009, ISBN: 981428212X | 9789814282123. |
Observation of Fermi polarons in a tunable Fermi liquid of ultracold atoms Journal Article Physical Review Letters, 102 (23), 2009, ISSN: 00319007 10797114. |
2008 |
Fermionic Superfluidity and the BEC-BCS Crossover in Ultracold Atomic Fermi Gases Inproceedings Ishioka, Sachio; Fujikawa, Kazuo (Ed.): Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology - ISQM Tokyo 2008, World Scientific, Tokyo, Japan, 2008. |
Making, probing and understanding ultracold Fermi gases Inproceedings Proceedings of the International School of Physics "Enrico Fermi", 2008, ISSN: 0074784X 18798195. |
2007 |
Coherence and clock shifts in ultracold fermi gases with resonant interactions Journal Article Physical Review Letters, 99 (19), 2007, ISSN: 00319007 10797114. |
Pairing without superfluidity: The ground state of an imbalanced fermi mixture Journal Article Science, 316 (5826), 2007, ISSN: 00368075 10959203. |
Superfluid Expansion of a Rotating Fermi Gas Journal Article Physical Review Letters, 98 (5), pp. 50404, 2007. |