Seminars are Wednesdays, 11:00AM–12 NOON
Haus Room, 36-428 (*unless otherwise noted)
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Spring 2021

March 3rd: Prof. Jens Eisert

Berlin Free University – Institut für Theoretische Physik
Semi-device-independent benchmarking, certification, and tomography

Abstract: At the same time as the development of quantum technologies progresses rapidly, new demands concerning the certification of their operation emerge. A question relevant for the application of various quantum technologies consequently is how the user can ensure the correct functioning of the quantum devices [1]. In a number of instances, specifically in quantum simulation and quantum computing, challenges in appropriately benchmarking components or entire protocols constitute a widely acknowledged bottleneck. This talk will suggest several new takes to the problem at hand: We will see how data from SPAM-robust randomized benchmarking [2] can be used to perform process tomography of quantum gates in an experimentally-friendly and provably sample optimal fashion [3], making use of a machinery of compressed sensing and exploiting structure – that is to say, the components of a quantum circuit. We will see how quantum states can be characterizes provably even with imperfect detectors in what could be called semi-device-dependent tomography [4]. The issue becomes more challenging when one aims at certifying the functioning of an entire device. We will look at limitations to black-box verification for sampling problems that show a quantum advantage or “supremacy” [5], will have a fresh look at Hamiltonian learning [6] and will see that in some instances [7], one can ironically certify the correctness of a device even if one cannot efficiently predict its performance. [1] Quantum certification and benchmarking, J. Eisert, D. Hangleiter, N. Walk, I. Roth, D. Markham, R. Parekh, U. Chabaud, E. Kashefi, Nature Reviews Physics 2, 382-390 (2020). [2] Randomized benchmarking for individual quantum gates, E. Onorati, A. H. Werner, J. Eisert, Phys. Rev. Lett. 123, 060501 (2019). [3] Recovering quantum gates from few average gate fidelities, I. Roth, R. Kueng, S. Kimmel, Y.-K. Liu, D. Gross, J. Eisert, M. Kliesch, Phys. Rev. Lett. 121, 170502 (2018). [4] Semi-device-dependent blind quantum tomography, I. Roth, J. Wilkens, D. Hangleiter, J. Eisert, arXiv:2006.03069 (2020). [5] Sample complexity of device-independently certified quantum supremacy, D. Hangleiter, M. Kliesch, J. Eisert, C. Gogolin, Phys. Rev. Lett. 122, 210502 (2019). [6] In preparation (2020). [7] J. Haferkamp, D. Hangleiter, A. Bouland, B. Fefferman, J. Eisert, and J. Bermejo-Vega, arXiv:1908.08069, Phys. Rev. Lett. (2020).

Bio: He is known for his research in and has made numerous contributions to quantum information science and quantum many-body theory in condensed matter physics. He has made significant contributions on entanglement theory and the study of quantum computational models, as well as quantum optical implementations of protocols in the quantum technologies and the study of complex quantum systems. He is also notable as one of the co-pioneers of quantum game theory with Maciej Lewenstein and PhD advisor Martin Wilkens.

11am
Via Zoom (https://mit.zoom.us/j/97518824305)

February 26th: Sri Krishna Vadlamani

UC Berkeley
Spectral Broadening in Tunnel Transistors and Physics-Based Machines for Discrete Optimization

Abstract: I shall talk about the two different projects in the field of energy-efficient computation that I worked on in my PhD:

Part 1 (Device Physics): Tunnel Field-Effect Transistors (tFETs) are one of the candidate devices being studied as energy-efficient alternatives to the present-day MOSFETs. In these devices, the preferred switching mechanism is the alignment (ON) or misalignment (OFF) of two energy levels or band edges. Unfortunately, energy levels are never perfectly sharp. When a quantum dot interacts with a wire, its energy level is broadened. Its actual spectral shape controls the current/voltage response of such transistor switches, from on (aligned) to off (misaligned). The most common model of spectral line shape is the Lorentzian, which falls off as reciprocal energy offset squared. Unfortunately, this is too slow a turnoff, algebraically, to be useful as a transistor switch. Electronic switches generally demand an ON/OFF ratio of at least a million. Steep exponentially falling spectral tails would be needed for rapid off-state switching. This requires a new electronic feature, not previously recognized: narrowband, heavy-effective mass, quantum wire electrical contacts, to the tunneling quantum states.

Part 2 (Systems Physics): Optimization is built into the fundamentals of physics. For example, physics has the principle of least action, the principle of minimum power dissipation, also called minimum entropy generation, and the adiabatic principle, which, in its quantum form, is called quantum annealing. Machines built on these principles can solve the mathematical problem of optimization, even when constraints are included. Further, these machines become digital in the same sense that a flip–flop is digital when binary constraints are included. A wide variety of machines have had recent success at optimizing the Ising magnetic energy. We demonstrate that almost all those machines perform optimization according to the principle of minimum power dissipation as put forth by Onsager. Moreover, we show that this optimization is equivalent to Lagrange multiplier optimization for constrained problems.

Bio: Sri Krishna Vadlamani (Sri) is a fifth-year PhD student in Prof. Eli Yablonovitch’s group in the EECS Dept. at UC Berkeley. He is interested in physics-based computation, both classical and quantum, with a particular interest in the potential impact of physics ideas on Machine Learning theory and applications. He received his undergraduate degree in Electrical Engineering from IIT Bombay, India, in 2016.

12pm
Via Zoom (https://mit.zoom.us/j/92408916520)

February 24th: Prof. Brian Gerardot

Heriot-Watt University
Quantum Light and Strongly Correlated Electronic States in a Moiré Heterostructure

Abstract: SThe unique physical properties of two-dimensional materials, combined with the ability to stack unlimited combinations of atomic layers with arbitrary crystal angle, has unlocked a new paradigm in designer quantum materials. For example, when two different monolayers are brought into contact to form a heterobilayer, the electronic interaction between the two layers results in a spatially periodic potential-energy landscape: the moiré superlattice. The moiré superlattice can create flat bands and quench the kinetic energy of electrons, giving rise to strongly correlated electron systems. Further, single particle wave packets can be trapped in the moiré potential pockets with three-fold symmetry to form ‘quantum dots’ which can emit single photons. Here I will present magneto-optical spectroscopy of a 2H-MoSe2/WSe2 heterobilayer device with ~3° twist. I will discuss moiré-trapped inter-layer excitons, which can emit quantum light, and intra-layer excitons, which exhibit a large number of strongly correlated electron and hole states as a function of fractional filling.

Bio: Professor Brian Gerardot holds a Chair in Emerging Technology from the Royal Academy of Engineering and leads the Quantum Photonics Lab at Heriot-Watt University in Edinburgh, Scotland (more information: http://qpl.eps.hw.ac.uk/). His research, at the interface of quantum optics, condensed-matter physics, and materials science, aims to engineer and controllably manipulate quantum states in semiconductor devices, in particular with III-V quantum dots and van der Waals heterostructure devices. Brian obtained a BS from Purdue University and a PhD in Materials Science from UC Santa Barbara.

11am
Via Zoom (https://mit.zoom.us/j/96268350649)

Winter 2021

February 17th: Eric I. Rosenthal

JILA
Efficient and low-backaction quantum measurement using a chip-scale detector

Abstract: Superconducting qubits are a leading platform for scalable quantum computing and quantum error correction. One feature of this platform is the ability to perform projective measurements orders of magnitude more quickly than qubit decoherence times. Such measurements are enabled by the use of quantum-limited parametric amplifiers in conjunction with ferrite circulators – magnetic devices which provide isolation from noise and decoherence due to amplifier backaction. Because these non-reciprocal elements have limited performance and are not easily integrated on-chip, it has been a longstanding goal to replace them with a scalable alternative. Here, we demonstrate a solution to this problem by using a superconducting switch to control the coupling between a qubit and amplifier. Doing so, we measure a transmon qubit using a single, chip-scale device to provide both parametric amplification and isolation from the bulk of amplifier backaction. This measurement is also fast, high fidelity, and has 70% efficiency, comparable to the best that has been reported in any superconducting qubit measurement. As such, this work constitutes a high-quality platform for the scalable measurement of superconducting qubits.

Bio: Eric I. Rosenthal is a Ph.D. student at the University of Colorado, Boulder, under the advisement of Professor Konrad Lehnert at JILA. He received his B.A. and M.S. in physics from the University of Pennsylvania in 2015 and is expected to receive his Ph.D. in physics in the spring of 2021. His research interest is in the advancement of quantum information technology using superconducting systems. In particular, his research has involved the development of superconducting switches, amplifiers, and non-reciprocal devices to improve the measurement of superconducting qubits.

11am
Via Zoom (https://mit.zoom.us/j/91675241753)

February 10th: Prof. Boubacar Kante

UC Berkeley
Topological light sources and sensors

Abstract: Topology plays a fundamental role in contemporary physics and enables new information processing schemes and wave device physics with built-in robustness. Recently, significant efforts have been devoted to transposing topological principles to bosonic systems. In the first part of this talk, I will discuss our invention of the first topological laser, a non-reciprocal light source capable of coupling stimulated emission to selected waveguide output in a controllable manner. I will also discuss unique optical devices based on this platform. In the second part of the talk, I will discuss our recently proposed scheme to systematically implement singularities known as exceptional points in passive plasmonics. I will discuss the new scheme and how we overcame current immuno-assay nano sensing record with plasmons by more than two orders of magnitude.

Bio: Boubacar Kanté is an associate professor of Electrical Engineering and Computer Sciences (EECS) at the University of California Berkeley. In 2010, he received a Ph.D degree in Engineering/Physics from “Université de Paris Sud” (Orsay-France). He was assistant professor and then associate professor of Electrical and Computer Engineering (ECE) at UC san Diego from 2013 to 2018. His research interests include wave-matter interaction and nano-optics. Boubacar Kanté is a 2020 Moore Inventor Fellow. He received the 2017 Office of Naval Research (ONR) Young Investigator Award, the 2016 National Science Foundation (NSF) Career Award, The best undergraduate teacher award from UC San Diego Jacob School of Engineering in 2017, the 2015 Hellman Fellowship, the Richelieu Prize in Sciences from the Chancellery of Paris Universities for the best Ph.D in France in Engineering, Material Science, Physics, Chemistry, Technology in 2010, the Young Scientist Award from the International Union of Radio Science (URSI) in Chicago in 2007, the Fellowship for excellence from the French Ministry of Foreign Affairs in 2003 for his undergraduate studies, a Research Fellowship from the French Research Ministry for his Ph.D studies.

11am
Via Zoom (https://mit.zoom.us/j/94195627674)

February 3rd: Dr. Martin Suchara

Argonne National Laboratory
Quantum Network Simulations – Towards Reliable, Scalable, and Secure Quantum Network Architectures

Abstract: Recent advances in quantum information science enabled the development of quantum communication network prototypes and created an opportunity to study full-stack quantum network architectures. This talk introduces SeQUeNCe, a comprehensive, customizable quantum network simulator. Our simulator consists of five modules: Hardware models, Entanglement Management protocols, Resource Management, Network Management, and Application. This modularized framework is suitable for simulation of quantum network prototypes that capture the breadth of current and future hardware technologies and protocols. We implement a comprehensive suite of network protocols and demonstrate the use of SeQUeNCe by simulating a quantum key distribution network, a teleportation network, and a metropolitan quantum network in the Chicago area consisting of nine routers equipped with quantum memories. Quantum network simulations are expected to play an increasingly important role in designing future quantum networks that scale to long distances and large number of hosts, and meet the latency, reliability and security needs of emerging applications. SeQUeNCe is freely available on GitHub.

Bio: Martin Suchara is a Computational Scientist at Argonne National Laboratory and at the University of Chicago with expertise in quantum computing and quantum communication. His group focuses on theoretical studies of photonic quantum networks, quantum error correction, quantum simulations, and optimizations of the quantum computing software stack. Dr. Suchara is the leader of the Simulation & Systems Thrust of the Q-NEXT National Quantum Information Science Research Center based at Argonne National Laboratory. Prior to joining Argonne he worked as a Principal Scientist at AT&T Labs and received postdoctoral training in quantum computing from UC Berkeley and the IBM T. J. Watson Research Center. Dr. Suchara received his PhD from the Computer Science department at Princeton University.

11am
Via Zoom (https://mit.zoom.us/j/97613945791)

January 27th: Dr. Amir Ghadimi

Swiss Center for Electronics and Micro/nano technology (CSEM)
Electro-optic and nonlinear photonic integrated circuit (PIC) platform based on lithium niobate on insulator (LNOI)

Abstract: Lithium niobate on insulator (LNOI) is one of the most promising emerging platforms for photonics integrated circuits (PICs) that comprises a unique set of interesting optical properties such as: a high electro-optic (EO) coefficient, high intrinsic 2nd and 3rd order nonlinearities, and a large transparency window (350 nm – 5500nm). Lithium niobate (LiN) has attracted a lot of attention since the 1970s, however, most of its industrial success has been limited to devices made from bulk LiN crystals in the form of free-space or fiber-coupled components using ion-implanted waveguides. Recent advancements in bonding of single crystal thin films of LiN onto silicon substrates (LNOI), opens a new avenue to explore the advantages of LiN in the context of PICs and to benefit from their miniaturization, cost reduction, scalable manufacturing and integration. In the LNIO platform, waveguides are fabricated using reactive ion etching (RIE) in a LiN thin film which allows for significantly higher refractive index contrast () compared to traditional waveguides made by ion implantation technology in bulk crystals (). This allows to reduce the optical mode volume by more than ~100x. Such high confinement not only results in more efficient and faster modulators but also in significantly smaller bending radii and PIC footprints, which, ultimately enables designing complex PICs with tens of components in a millimeters-size chips. In an LNOI platform we can combine high performance active EO components such as modulators, phase shifters and tunable cavities with unique optical nonlinearities at a wide range of wavelengths to achieve truly novel functionalities and PIC designs that are beyond the capabilities of any PIC platform commercially available today. In this talk I will present the recent progress at CSEM toward developing an EO and nonlinear PIC platform based on LNOI. We start by reviewing the advantages of LNOI platform for various application areas such as telecom, optical signal processing, programmable PICs, LiDAR, spectroscopy, quantum information processing, and nonlinear photonic. Then we will review how LNOI platform fits within the industrial PIC ecosystem and how it compares with other PIC platforms such as Si, SiN and InP. We then discuss the challenges in fabricating high quality photonics circuits in LNOI and will review CSEM’s recent results in design, fabrication, and testing of high quality LNOI photonic circuits. Next, we briefly review few successful example and experiments performed by CSEM or in collaboration with other groups in the areas of nonlinear photonics and quantum information processing. Finally, I will present the future perspectives of our LNOI platform including the process design kit (PDK) library and the means that interested parties can access our platform as a pre-commercial foundry service.

Bio: Dr. Amir H. Ghadimi is currently a senior scientist and a group leader at the Swiss Center for Electronics and Micro/nano technology (CSEM). He is currently leading the efforts at CSEM in the areas of PICs and PIC based sensing where together with his team they are developing two PIC platforms based on SiN and LNOI. He obtained his PhD. in electrical engineering in 2018 from the Swiss Federal Institute of Technology (EPFL). His PhD research focused on quantum optomechanics, precision sensing and applications of high Q optical and mechanical resonators. He is the recipient of Swiss national funding (SNF) Bridge discovery grant (2020), Swiss Physical Society (SPS) 2019 young scientist award, Swiss Nanotechnology best PhD award (2018) and European frequency and time forum (EFTF) best paper award (2018).

11am
Via Zoom (https://mit.zoom.us/j/95001956600)

January 20th POSTPONED: Professor Jens Eisert

Berlin Free University – Institut für Theoretische Physik
Semi-device-independent benchmarking, certification, and tomography

Abstract: At the same time as the development of quantum technologies progresses rapidly, new demands concerning the certification of their operation emerge. A question relevant for the application of various quantum technologies consequently is how the user can ensure the correct functioning of the quantum devices [1]. In a number of instances, specifically in quantum simulation and quantum computing, challenges in appropriately benchmarking components or entire protocols constitute a widely acknowledged bottleneck. This talk will suggest several new takes to the problem at hand: We will see how data from SPAM-robust randomized benchmarking [2] can be used to perform process tomography of quantum gates in an experimentally-friendly and provably sample optimal fashion [3], making use of a machinery of compressed sensing and exploiting structure – that is to say, the components of a quantum circuit. We will see how quantum states can be characterizes provably even with imperfect detectors in what could be called semi-device-dependent tomography [4]. The issue becomes more challenging when one aims at certifying the functioning of an entire device. We will look at limitations to black-box verification for sampling problems that show a quantum advantage or “supremacy” [5], will have a fresh look at Hamiltonian learning [6] and will see that in some instances [7], one can ironically certify the correctness of a device even if one cannot efficiently predict its performance.

[1] Quantum certification and benchmarking, J. Eisert, D. Hangleiter, N. Walk, I. Roth, D. Markham, R. Parekh, U. Chabaud, E. Kashefi, Nature Reviews Physics 2, 382-390 (2020).
[2] Randomized benchmarking for individual quantum gates, E. Onorati, A. H. Werner, J. Eisert, Phys. Rev. Lett. 123, 060501 (2019).
[3] Recovering quantum gates from few average gate fidelities, I. Roth, R. Kueng, S. Kimmel, Y.-K. Liu, D. Gross, J. Eisert, M. Kliesch, Phys. Rev. Lett. 121, 170502 (2018).
[4] Semi-device-dependent blind quantum tomography, I. Roth, J. Wilkens, D. Hangleiter, J. Eisert, arXiv:2006.03069 (2020).
[5] Sample complexity of device-independently certified quantum supremacy, D. Hangleiter, M. Kliesch, J. Eisert, C. Gogolin, Phys. Rev. Lett. 122, 210502 (2019).
[6] In preparation (2020).
[7] J. Haferkamp, D. Hangleiter, A. Bouland, B. Fefferman, J. Eisert, and J. Bermejo-Vega, arXiv:1908.08069, Phys. Rev. Lett. (2020).

Bio: He is known for his research in and has made numerous contributions to quantum information science and quantum many-body theory in condensed matter physics. He has made significant contributions on entanglement theory and the study of quantum computational models, as well as quantum optical implementations of protocols in the quantum technologies and the study of complex quantum systems. He is also notable as one of the co-pioneers of quantum game theory with Maciej Lewenstein and PhD advisor Martin Wilkens.

11am
Via Zoom (https://mit.zoom.us/j/97518824305)

January 13th: Dr. Kin Chung Fong

Raytheon BBN Technologies
Graphene-based single-photon detector for quantum information science and astrophysics

Abstract: High sensitivity photon detectors are essential in qubit measurement and remote entanglement, as well as dark matter detection and observing the cosmic infrared background in astrophysics. However, sensing in microwave and far-infrared spectrum is challenging because of the low photon energy. In this talk, we will present how to leverage the giant thermal response of graphene electrons for photon detection. Interestingly, when our graphene bolometer achieves a record-high sensitivity of 10-19 W/Hz1/2, this sensitivity is limited, no longer by extrinsic factors but, by the statistical thermal fluctuation intrinsic to the graphene electrons as a canonical ensemble at 0.2 K [1]. Using the graphene-based Josephson junction, we demonstrate the single-photon detection in the infrared regime by observing the photon shot noise [2]. As an outlook, we will discuss how the unique properties of two-dimensional materials will open new opportunities in quantum information science.

[1] Nature 586, 42 (2020) [2] arXiv:2011.02624.

Bio: Born and raised in Hong Kong, Dr. Kin Chung Fong came to the United States to pursue his PhD under the supervision of Prof. Chris Hammel at Ohio State University. This is where KC develops his passion on high sensitivity experiments to observe new physical phenomena that cannot be otherwise measured. These include detecting a single electron spin magnetic resonance for nanoscale MRI, measuring superconducting qubits with quantum-limit amplifications, and detecting Dirac fluid in graphene. After his postdoc at Caltech, KC joined BBN Technologies in 2013. His research now focuses on studying the fundamental physics of strongly interacting Dirac and Weyl fermions in condensed matter systems with their connections to holographic principle, and developing the Josephson junction single photon detector for quantum information science, radioastronomy, and the search of dark matter axions. KC loves spending time outdoor with his family during weekends and learning new things from friends and collaborators, especially over a coffee!

11am
Via Zoom (https://mit.zoom.us/j/93266078938)


Image credit: Greg Steinbrecher