Group of Vladan Vuletic
Experimental Atomic Physics
Center for Ultracold Atoms and Research Laboratory of Electronics
Department of Physics, Massachusetts Institute of Technology


Vladan Vuletic
Lester Wolfe Associate Professor of Physics
MIT Room 26-231    Location on MIT campus
77 Massachusetts Avenue
Cambridge, MA 02139-4309
phone (617) 324-1174
fax     (617) 253-4876
@mit.edu

Adminstrative contact: Joanna Keseberg, (617) 253-6830 (phone), (617) 253-4876 (fax), j_k@MIT.EDU
Mailing address: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 26-231, Cambridge, MA 02139-4309

 

Group members (for email add @mit.edu, for picture click on name)
 
Name
Position
office
   lab 
phone (office/lab)
email
Bloom, Ben
Undergraduate
26-230
(617) 452-3578
bbloom
Cetina, Marko
Research Assistant

26-225
26-230
 (617) 452-3578
mcetina
Ghosh, Saikat

Postdoc

  
26-230
617) 253-4167

saikatg

Grier, Andrew

Research Assistant

26-225
26-230
(617) 452-3578
agrier
Leroux, Ian
Research Assistant

26-221
26-228
(617) 452-3578
idleroux
Orucevic, Fedja

Postdoc

26-225

26-230
(617) 452-3578
orucevic
Peyronel, Thibault

Research Assistant

26-221

26-3xx
(617) 452-3578
peyronel
Pruttivarasin, Thaned
Undergraduate

26-230
(617) 452-3578
thanedp
Schwab, Adele
Undergraduate

26-228
(617) 452-3578
aschwab
Schleier-Smith, Monika
Research Assistant

26-221
26-228
(617) 452-3578
schleier
Simon, Jonathan
Research Assistant

26-225
26-230
(617) 253-4167
simonj
Tanji, Haruka
Research Assistant

26-225
26-230
(617) 253-4167

tanji

Vuletic, Vladan
Associate Professor
26-231
  
(617) 324-1174
vuletic
* add @fas.harvard.edu
 

Past group members

Black, Adam               (PhD Stanford/MIT 2005, now working on atom interferometry in Mountain View, CA)
Brown, David             (Senior Thesis MIT 2007, now graduate student at Caltech)

Campbell, Jonathan     (Master Thesis MIT 2006, now at West Point)
Chan, Hilton                (PhD Stanford 2003, now with Ball Aerospace, Boulder, CO)
Chu, Yiwen                 (Senior Thesis MIT 2007, now graduate student at Harvard)

Childress, Michael       (Senior Thesis MIT 2005, now graduate student at Berkeley)
Lin, Yu-ju                   (PhD Stanford/MIT 2007, now postdoc at NIST, Gaithersburg, with Bill Phillips' group)
Loh, Huanqian          (Senior Thesis MIT 2006 (Apker thesis award of the APS), now graduate student in Boulder, CO)
Shields, Brendan        (Senior Thesis MIT 2006, now graduate student at Harvard)
Teper, Igor                  (PhD Stanford/MIT 2006, now postdoc at Stanford with Mark Kasevich's group)
Thompson, James        (Postdoc 2003-2006, now Assistant Professor at the University of Colorado in Boulder/JILA)
Cheng, Chin                (Postdoc 2001-2003, now Assistant Professor at the University of Chicago)
 

 

Current research

We are currently working on three experiments, and preparing a fourth one: The first is concerned with generating single photons using an ensemble of laser-cooled atoms in an optical resonator. The second experiment uses currents flowing through conductors on a microfabricated chip to create and trap Bose-Einstein condensates, where we are currently trying to realize an atomic clock operating below the atom-number shot-noise limit (standard quantum limit). We are also building an ion trap experiment using Ytterbium ions for quantum computation and communication. Finally, in collaboration with Prof. Mikhail Lukin's Harvard group, we are setting up an experiment for using cold atoms inside a hollow-core optical fiber to generate non-classical light at the single-photon level. The long term goal of all experiments is to develop new methods to manipulate particles in a regime where the quantum mechanical aspects dominate their behavior and their properties. On the one hand, this should lead to new tools that allow one to probe physical laws and to measure fundamental constants with increasing precision. On the other hand, the progress of experimental methods also drives the advances in our understanding of the ever mysterious, beautiful, accurate, yet deeply dissatisfying structure of quantum mechanics. This interplay between theoretical concepts and experimental realizations promises to be very fertile in fields such as quantum control, quantum feedback and its limits, many-particle quantum systems, and many-particle entanglement (quantum computing). 

 

Coupling many atoms to single photons: single-photon source and beyond

The collective interaction of many atoms with a single mode of an optical resonator also allows one to prepare entangled states of large samples of atoms by detection of the photons emitted by the atoms. When the atoms interact with the mode in a way that makes it fundamentally impossible to determine which atoms, e.g. emitted a photon into the resonator, the system must be described by an entangled state of the atomic ensemble (Dicke state). Under appropriate conditions, these states interact collectively, and therefore very strongly with photons.
    Following a slightly modified version of the quantum repeater proposal by Duan, Lukin, Cirac, and Zoller [1], we have built a system where a sample of atoms is made to conditionally generate a single photon on demand following the (random) detection of a previous single photon. Currently we are able to store the excitation corresponding to a single photon for 2 us as a ground-state polarization grating (spin wave) in the atomic sample containing 106 atoms, and to convert this excitation into a single photon with an efficiency near 90%. The storage time is limited by the Doppler effect, i.e. by the random thermal motion of the atoms that destroys the holographic grating. We are working on increasing the storage time into the range of milliseconds, and possibly seconds, by decreasing the Doppler effect, and ultimately removing it altogether by strong confinement of the atoms (Lamb-Dicke regime). We also expect to be able to further increase the read efficiency, producing an even better approximation to a single-photon Fock state on demand.

[1]    L.M. Duan. M.D. Lukin, J.I. Cirac, and P.Zoller, Nature 414, 413 (2001).

Article in Physics@MIT: "Generating Single Photons on Demand", PDF. 
News&Views in Nature Physics: "When Superatoms Talk Photons", on J. Kimble's work interfering photons from two sources, PDF.

 

New laser cooling methods for atoms, ions or molecules: Cavity Doppler cooling and cavity sideband cooling by coherent scattering

Laser cooling of atoms has not only supplied the basis for the control and manipulation of matter at the quantum limit, e.g. in form of Bose-Einstein condensation, but has also resulted in a number of important applications and devices, many of which are tied to precision measurements and atomic clocks. However, laser cooling has so far been limited to atoms with a particular internal structure, and the cooling of molecules or even of atoms with a complicated level scheme has not been possible. If we could learn how to cool, trap and manipulate larger molecules in the same way as atoms, this would open the door for important developments in chemistry and possibly even in biology.
    Doppler cooling [2] is the dominant laser cooling mechanism at all but the lowest temperatures. In Doppler cooling counterpropagating laser beams are tuned to the red of a closed transition between an atomic ground and an atomic excited state. An atom that is moving towards a laser beam will experience photons that are blue-shifted into resonance with the atomic transition, while photons from a beam propagating in the same direction as the atom will be red-shifted further out of resonance. The momentum transfer associated with the preferred absorption of photons from the counterpropagating beam leads to slowing and cooling of the atoms, while the randomly emitted photons on average do not contribute to the force. The net effect is cooling to temperatures in the millikelvin to microkelvin range, corresponding to atomic velocities in the range of a few millimeters to a few centimeters per second.
    This principle behind laser cooling also entails its limitation. Since the momentum “kick” associated with each photon absorption event is much smaller than the momentum of a thermal atom, a larger number of absorption-emission events (on the order of thousand or more) is required to significantly change the atom’s velocity. Therefore laser cooling has only been demonstrated with atoms that can be optically cycled many times back to their initial ground state. However, most atoms (and all molecules) have multiple ground states to which the excited state can decay. Once the atom reaches a different ground state, the laser no longer has the correct detuning relative to the atomic transition, and the cooling stops. In particular, molecules have many vibrational and rotational levels, and consequently no laser cooling of molecules has been demonstrated.
    The novel proposed method [3,4] is based on coherent scattering, rather than on spontaneous emission from an excited state. Coherent scattering dominates when the laser is far detuned from atomic or molecular transitions and when its intensity is not too large. Coherent scattering is generic to all polarizable particles, independent of their internal structure, and describes the emission of radiation by an oscillating atomic dipole that is driven by an external (classical) electric field. The basic idea behind the proposed technique is that energy is conserved in the scattering process, and that therefore events where the scattered photon carries away a larger energy than the incident-photon energy are accompanied by a corresponding reduction of the atom’s energy. Such scattering events can be enhanced in an optical resonator that is tuned to be resonant with a frequency that is higher than that of the incident light. The new cooling mechanism depends only on the finesse (i.e. on the reflectivity of the cavity mirrors) and on the detuning of the photons relative to the cavity resonance, while it is independent of the detuning relative to atomic transitions. Therefore this new technique should be generic and be applicable to any sort of material. The target can be an atom in different ground states, a molecule in different rotational and vibrational states, or possibly even a scattering center (impurity) inside a solid. The only requirement is that at the given intensity and laser frequency the emission rate by the scatterer is large enough to produce efficient cooling. The cooling power is given by the product of the scattering rate and the energy difference between the incident and the scattered photon [3].
    When we performed what was to be a proof-of-principle experiment with cesium atoms inside an optical resonator, we found very much to our surprise that both the light emitted by the atoms into the cavity, and the cavity-emission-induced forces on the atoms were much larger than expected for independent atoms [5,6]. In some cases [6] the observed emission and forces exceeded the predicted single-atom values [2-4] by a factor of a few thousand! The observed laser-like collective emission by the atomic sample required an optical gain mechanism. For not too large light-atom detunings, where the atomic multilevel structure is relevant, we obtained experimental evidence that the optical gain is Raman gain between differently populated magnetic sublevels. In the limit of large detuning, where the atomic multilevel structure is negligible, and the atoms behave like classical light scatterers, Domokos and Ritsch from the University of Innsbruck suggested that the collective emission could be explained by a collective process where the atoms self-organize into a density grating [8]. Then the classical (Rayleigh) emission by individual atoms, proportional to the number of atoms N, would be transformed into Bragg scattering by the density grating, scaling as N 2. We have verified those predictions experimentally by measuring the phase of the light emitted into the cavity, and furthermore observed a very strong cooling of the sample's center-of-mass motion [7].

[2]    T.W. Hänsch and A.L. Schawlow, Opt. Commun. 13, 68 (1975).
[3]    V. Vuletic and S. Chu, Phys. Rev. Lett. 84, 3787 (2000).
[4]    P. Horak, G. Hechenblaikner, K.M. Gheri, H. Stecher, and H. Ritsch, Phys. Rev. Lett. 79, 4974 (1997).
[5]    V. Vuletic, H. W. Chan, and A. T. Black, Phys. Rev. A 64, 033405 (2001).
[6]    H.W. Chan, A.T. Black, and V. Vuletic, Phys. Rev. Lett. 90, 063003 (2003).
[7]    A.T. Black, H.W. Chan, and V. Vuletic, Phys. Rev. Lett. 91, 203001 (2003).
[8]    P. Domokos and H. Ritsch, Phys. Rev. Lett. 89, 253003 (2003).
 

 

Bose-Einstein condensates on a microchip: Casimir-Polder potential, Johnson noise, matter wave interferometry, and beyond

    We have built a microchip-based magnetic trap where we can evaporate Rb atoms in less than 3s to Bose-Einstein condensation (BEC). The simple setup uses a standard magneto-optical trap, subsequent magnetic transport of the sample to within 60 mm of the chip surface, and microwave-induced forced evaporation to BEC. Since further trap miniaturization will require the atoms to be placed even closer to the field-generating elements, we have explored the effect of a room-temperature surface on the 100 million times colder condensate [9]. In agreement with previous theoretical [10] and experimental [11,12] results, we find that the lifetime near a metal surface is limited by Johnson-noise induced thermal currents, while a non-conducting surface is benign. In the latter case the atoms remain trapped until the attractive Casimir-Polder substantially reduces the trap depth.
    The above results suggest that the local manipulation of condensates will be possible using thin conductors, which have low magnetic field noise, on dielectric surfaces. With the next generation of microchips, we hope to attain radial vibration frequencies up to 1MHz, and to observe coherent tunneling through a thin potential barrier. The combination of two such barriers provides a Fabry-Perot resonator for atomic matter waves. Since for interacting atoms the energy levels depend on the number of atoms inside the resonator, the system should be equivalent to a single-electron transistor in the limit where the two-atom interaction energy is larger than the resonator level spacing. Such atomic quantum devices should be very interesting for fundamental science with degenerate gases, as well as from an quantum engineering point of view.
    We have recently implemented single-atom detection on a microchip using an optical resonator [13]. Currently we are trying to produce entangled (squeezed) states of many atom by resonator-induced observation. These quantum mechanical many-body states, where the state of each individual atom is uncertain, but the states of different atoms are correlated, should allow one to improve precision devices, such as atomic clocks, beyond the limit set by atomic shot noise. The latter is the projection noise arising from the measurement of the state of each atom, where each atom randomly, and independent of the state of the other atoms, chooses one state as the outcome of a measurement. The corresponding limit on the measurement precision is called the "standard quantum limit". Quantum mechanical correlations between the atoms allow one to reduce the measurement noise below the standard quantum limit, because the atoms no longer choose their final state independently from the choices made by the previous atoms.

[9]    Y. Lin, I. Teper, C. Chin, and V. Vuletic, Phys. Rev. Lett. 92, 050404 (2004).
[10]  C. Henkel, S. Potting, and M. Wilkens, Appl. Phys. B 69, 379 (1999); C. Henkel and S. Potting, ibid. 72, 73 (2001).
[11]  M.P.A. Jones, C. J. Vale, D. Sahagun, B.V. Hall, and E.A. Hinds, Phys. Rev. Lett. 91, 080401 (2003).
[12]  D.M. Harber, J.M. McGuirk, J.M. Obrecht, and E. A. Cornell, J. Low Temp. Phys. 133, 229 (2003).
[13]  I. Teper, Y. Lin, and V. Vuletic, Phys. Rev. Lett. 97, 023002 (2006).

 

 

 

 

 

    Microchip traps for Bose-Einstein condensates or ions