# Virtual Seminar Series

## Virtual Seminar Series

**Click here** to view the schedule for upcoming seminars.

Starting in June 2020, we are hosting a series of online talks about topics related to **Quantum Information Sciences** in its various forms, including (but not limiting to):

- Quantum computers
- Quantum simulation
- Measuring the elusive Majorana fermion
- Photons

Talks will be given by senior researchers as well as students and postdocs.

##### Seminars are organized in collaboration with Roy Araiza, Gaurav Bahl and Angela Kou. Please feel free to reach out to them by e-mail with any comments and suggestions.

##### Click here to subscribe to our weekly event mailing list for upcoming seminars.

**Past Talks - Fall 2022**

## Tuesday, November 29 | 11:00 a.m. CST

Eilon Poem "Single-Photon Generation, Storage, Synchronization, and Interaction in Hot Atomic Vapor"

Complex quantum states of light, containing many photons entangled over many modes, are important for a variety of quantum technology applications, from demonstrations of quantum advantage, through super-sensitive metrology, to measurement-based quantum computation. The creation of such states in a scalable manner has been, and to a large extent, still is, a standing scientific and engineering challenge.

In this talk, I will present our continuing work toward the creation of such complex quantum states of light using a relatively simple and potentially scalable system: a set of atomic vapor cells at or above room temperature. I will discuss our implementations of two of the three necessary components for such a feat: a noise-free quantum memory [1,2] and two identical, memory-compatible single-photon sources [3]. I'll also present very recent results demonstrating active synchronization of the photon sources by using the memory. Finally, I'll discuss our path toward the third ingredient, a few-photon-level non-linear component.

1. R. Finkelstein et al., Science Advances 4, eaap8598 (2018)

2. R. Finkelstein et al., Phys. Rev. X 11, 011008 (2021)

3. O. Davidson et al., New J. Phys. 23, 073050 (2021)

## Tuesday, November 15 | 11:00 a.m. CST

Markus Aspelmeyer "Quantum Optomechanics of Levitated Solids"

**Abstract**: The quantum optical control of solid-state mechanical devices, quantum optomechanics, has emerged as a new frontier of light-matter interactions. Objects currently under investigation cover a mass range of more than 17 orders of magnitude - from nanomechanical waveguides to macroscopic, kilogram-weight mirrors of gravitational wave detectors. Extending this approach to levitated solids opens up complete new ways of coherently controlling the motion of massive quantum objects in engineerable potential landscapes. I will discuss recent experimental advances in quantum controlling levitated solids, including demonstrations of the motional quantum ground state of optically trapped nanoparticles in a room temperature environment, and of unconventional light-induced dipole-dipole interactions between two particles. I will also discuss the perspective to explore new regimes of macroscopic quantum physics, in particular ones that include quantum systems as sources of gravity.**Bio**: Markus Aspelmeyer is a Professor of Physics at the University of Vienna and Scientific Director at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences in Vienna. He studied physics and philosophy in Munich, Germany. Aspelmeyer is regarded one of the pioneers of the field of quantum optomechanics. His research combines the development of new quantum technologies with fundamental quantum experiments. He is co-founder of Crystalline Mirror Solutions (now Thorlabs Crystalline Solutions), which provides novel optics for laser precision measurements. He is a Fellow of the American Physical Society, and Member of the Austrian Academy of Sciences and the Academy of Sciences and Humanities in Hamburg. His current research is focused on the intriguing puzzles around quantum physics and gravity.

## Tuesday, November 1 | 11:00 a.m. CST

Alexander Müller-Hermes "Fault-tolerant Coding for Quantum Communication"

**Abstract**: Designing encoding and decoding circuits to reliably send messages over many uses of a noisy channel is a central problem in communication theory. When studying the optimal transmission rates achievable with asymptotically vanishing error it is usually assumed that these circuits can be implemented using noise-free gates. While this assumption is satisfied for classical machines in many scenarios, it is not expected to be satisfied in the near term future for quantum machines where decoherence leads to faults in the quantum gates. As a result, fundamental questions regarding the practical relevance of quantum channel coding remain open.

By combining techniques from fault-tolerant quantum computation with techniques from quantum communication, we initiate the study of these questions. We introduce fault-tolerant versions of quantum capacities quantifying the optimal communication rates achievable with asymptotically vanishing total error when the encoding and decoding circuits are affected by gate errors with small probability. Our main results are threshold theorems for the classical and quantum capacity:

For every quantum channel T and every ϵ > 0 there exists a threshold p(ϵ, T) for the gate error probability below which rates larger than C-ϵ are fault-tolerantly achievable with vanishing overall communication error, where C denotes the usual capacity. Joint work with Matthias Christandl.**Bio**: Alexander Müller-Hermes received the Ph.D. degree in 2015 from the Technical University of Munich. After being a postdoc at the Centre of Mathematics in Quantum Theory (QMATH) at the University of Copenhagen, he obtained a Marie SkłodowskaCurie fellowship at Institute Camille Jordan at the Université Claude Bernard Lyon 1. Since 2021, he is associate professor at the Department of Mathematics at the University of Oslo. His research interests include the mathematical aspects of quantum information theory, quantum Shannon theory, mathematical cake cutting, and entanglement theory.

## Tuesday, October 25 | 11:00 a.m. CST

Florian Marquardt "Reinforcement Learning for Quantum Technologies"

**Abstract**: In this talk, I will illustrate how a set of techniques from computer science that go under the name of reinforcement learning can be helpful in modern quantum devices. These techniques allow to discover from scratch quantum control and feedback strategies, which can help to prepare and stabilize quantum states and perform quantum error correction. In addition, whole quantum circuits can be optimized with the help of these approaches. Beyond our theoretical proposals in this area I will also discuss the first reinforcement learning of real-time quantum feedback in an experiment, performed in a collaboration with the superconducting-qubit team at ETH.**Bio:** Florian Marquardt is a theoretical physicist whose current focus is on applying machine learning to scientific discovery and discovering physical systems that help for machine learning. He has a long-standing track record in areas bridging nanophysics and quantum optics, among them significant contributions to the theory of cavity optomechanics and the theory of superconducting circuit quantum electrodynamics. He is currently a scientific director at the Max Planck Institute for the Science of Light in Erlangen, Germany, as well as a professor at the local university. He studied at the university of Bayreuth, Germany, then did his PhD in Basel, Switzerland (finishing in 2002), afterwards went on to a postdoctoral stay at Yale university and a junior research group leader position at the university of Munich, before moving to Erlangen.

## Tuesday, October 18 | 11:00 a.m. CST

Jake Taylor "The Birth of Quantum Engineering"

**Abstract: **Quantum technologies provide new base capabilities which open up frontiers in sensing, networking, and computation. In all cases, working at the limits set by nature requires high degrees of integration of complex systems to realize practical results. I will discuss the promise quantum systems in diverse areas from particle physics to drug discovery, and highlight the many challenges to be overcome and the ways in which the nascent field of quantum engineering can tackle these challenges.

**Bio**: Jake’s research career in quantum information science spans two decades, and includes pioneering work in semiconductor-based qubits, superconductor-based qubits, quantum transducers, topological photonics, and diamond-based quantum sensors. From 2017-2020, Jake led the U.S. effort in creating and implementing the National Quantum Initiative while at the White House Office of Science and Technology Policy. A fellow of the American Physical Society and of Optica (formerly OSA), Jake has also been awarded the silver and gold medals by the U.S. Department of Commerce for his research and his work in advancing quantum information science.

## Tuesday, October 4 | 11:00 a.m. CST

Sabre Kais "Quantum Machine-Learning for Complex Many-Body Systems"

**Abstract: **In this talk, I will focus on quantum machine learning, particularly the Restricted Boltzmann Machine (RBM), as it emerged to be a promising alternative approach leveraging the power of quantum computers. Such algorithms have been developed to solve problems like electronic structure calculations of molecular systems and spin models in magnetic systems. However, the discussion in all these recipes focuses specifically on targeting the ground state. Herein we demonstrate a quantum algorithm that can filter any energy eigenstate of the system based on either symmetry properties or a predefined choice of the user. The workhorse of our technique is a shallow neural network encoding the desired state of the system with the amplitude computed by sampling the Gibbs−Boltzmann distribution using a quantum circuit and the phase information obtained classically from the nonlinear activation of a separate set of neurons. We implement our algorithm not only on quantum simulators but also on actual IBM-Q quantum devices and show good agreement with the results procured from conventional electronic structure calculations.

Finally, I will discuss and illustrate that the imaginary components of out-of-time correlators can be related to conventional measures of correlation like mutual information. Such an analysis offers important insights into the training dynamics by unraveling how quantum information is scrambled through such a network introducing correlation among its constituent sub-systems. This approach not only demystifies the training of quantum machine learning models but can also explicate the capacitive quality of the model.**Bio**: Sabre Kais received the BSc, MSc, and Ph.D. degrees at the Hebrew University of Jerusalem in 1983, 1984 and 1989, respectively. From 1989 to 1994, he was a research associate at Harvard University, Department of Chemistry. He joined Purdue University in 1994 as an Assistant Professor of Theoretical Chemistry. Currently, he is a distinguished Professor of Chemical Physics, a Professor of Computer Science (courtesy) a professor of Physics at Purdue University. He has published over 260 papers in peer-reviewed journals. The research in his group is mainly devoted to finite size scaling, dimensional scaling, quantum information, and quantum computing for complex systems. He was the director of NSF funded center of innovation on “Quantum Information for Quantum Chemistry”, from 2010-2013. He served as an External Research Professor at Santa Fe Institute from 2013-2019. He is a Fellow of the American Physical Society, Fellow of the American Association for the Advancement of Science, Guggenheim Fellow, Purdue University Faculty Scholar, National Science Foundation Career Award Fellow, 2012 Sigma Xi Research Award, and 2019 Herbert Newby McCoy Award, Purdue University.

## Tuesday, September 27 | 11:00 a.m. CST

Michael E. Flatté "Coherent Magnonics for Quantum Information Science"

**Abstract**: The current revolution in quantum technologies relies on coherently linking quantum objects like quantum bits (“qubits”). Coherent magnonic excitations of low-loss magnetic materials can wire together these qubits for sensing, memory, and computing. Coherent magnonics may reduce the size of superconducting qubits (which otherwise struggle with the large scale of microwave excitations) and may increase the size of spin-based qubit networks (which otherwise contend with the very short distances of dipolar or exchange interactions). Compared to photonic devices, these magnonic devices require minimal energy and space. However, efforts to exploit coherent magnonic systems for quantum information science will require a new understanding of the linewidths of low-loss magnonic materials shaped into novel structures and operating at dilution-refrigerator temperatures.

This lecture will introduce the fundamental requirements for practically linking quantum objects into large-scale coherent quantum systems as well as the advantages of coherent magnonics for next-generation quantum coherent systems (i.e., spin-entangling quantum gates [1]). Other critical challenges for quantum information science then will motivate the development of coherent magnonics for quantum transduction from “stationary” spin systems to “flying” magnons and for quantum memory [2]–[4]. Finally, the advantages of all-magnon quantum information technologies that rely on manipulating and encoding quantum information in superpositions of fixed magnon number states will highlight the potential of new magnetic materials, devices, and systems.

**Bio: **Michael E. Flatté (Member, IEEE) received the A.B. degree in physics from Harvard University, Cambridge, MA, USA, in 1988, and the Ph.D. degree in physics from the University of California at Santa Barbara, Santa Barbara, CA, USA, in 1992. He is a Professor at the Department of Physics and Astronomy, The University of Iowa (UI), Iowa City, IA, USA. After his post-doctoral work at the Institute for Theoretical Physics, University of California at Santa Barbara, and the Division of Applied Sciences, Harvard University, he joined the faculty at UI in 1995. He has over 270 publications and ten patents. He has an adjunct appointment as a Professor at the Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands. His research interests include optical and electrical control of spin dynamics in materials, novel spintronic devices, quantum sensors, and solid-state realizations of quantum computation. Dr. Flatté is a fellow of the American Association for the Advancement of Science and the American Physical Society.

## Tuesday, September 6 | 11:00 a.m. CST

Prineha Narang "Building Blocks of Scalable Quantum Information Science "

**Abstract**: Quantum information technologies are expected to enable transformative technologies with wide-ranging global impact. Towards realizing this tremendous promise, efforts have emerged to pursue quantum architectures capable of supporting distributed quantum computing, networks and quantum sensors. Quantum architecture at scale would consist of interconnected physical systems, many operating at their individual classical or quantum limit. Such scalable quantum architecture requires modeling that accurately describes these mesoscopic hybrid phenomena. By creating predictive theoretical and computational approaches to study dynamics, decoherence and correlations in quantum matter, our work could enable such hybrid quantum technologies1,2. In this talk, I will present examples from my research group on describing, from first principles, the microscopic dynamics, decoherence and optically-excited collective phenomena in matter at finite temperature to quantitatively link predictions with 3D atomic-scale imaging, quantum spectroscopy, and macroscopic behavior. Capturing these dynamics poses unique theoretical and computational challenges. The simultaneous contribution of processes that occur on many time and length-scales have remained elusive for state-of-the-art calculations and model Hamiltonian approaches alike, necessitating the development of new methods in computational physics3–5. I will show selected examples of our approach in *ab initio* design of active defects in quantum materials6–8, and control of collective phenomena to link these active defects9,10. Building on this, in the second part of my seminar, I will present promising physical mechanisms and device architectures for coupling (transduction) to other qubit platforms *via* dipole-, phonon-, and magnon-mediated interactions9–12. In a molecular context, will discuss approaches to entangling molecules in the strong coupling regime. Being able to control molecules at a quantum level gives us access to degrees of freedom such as the vibrational or rotational degrees to the internal state structure. Entangling those degrees of freedom offers unique opportunities in quantum information processing, especially in the construction of quantum memories. In particular, we look at two identical molecules spatially separated by a variable distance within a photonic environment such as a high-Q optical cavity. By resonantly coupling the effective cavity mode to a specific vibrational frequency of both molecules, we theoretically investigate how strong light-matter coupling can be used to control the entanglement between vibrational quantum states of both molecules. Linking this with detection of entanglement and quantifying the entanglement with an appropriate entanglement measure, we use quantum tomographic techniques to reconstruct the density matrix of the underlying quantum state. Taking this further, I will present some of our recent work in capturing non-Markovian dynamics in open quantum systems (OQSs) built on the ensemble of Lindblad's trajectories approach 13–16. Finally, I will present ideas in directly emulating quantum systems, particularly addressing the issues of model abstraction and scalability, and connect with the various quantum algorithm efforts underway.**Bio: **Dr. Prineha Narang is a Professor in Physical Sciences at UCLA holds the Howard Reiss Chair, where her group spans chemistry, physics, and engineering. Prior to moving to UCLA, she was an Assistant Professor of Computational Materials Science at Harvard University. Before starting on the Harvard faculty in 2017, Dr. Narang was an Environmental Fellow at HUCE, and worked as a research scholar in condensed matter theory in the Department of Physics at MIT. She received an M.S. and Ph.D. in Applied Physics from Caltech. Narang’s work has been recognized by many awards and special designations, including the 2022 Outstanding Early Career Investigator Award from the Materials Research Society, Mildred Dresselhaus Prize, Bessel Research Award from the Alexander von Humboldt Foundation, a Max Planck Award from the Max Planck Society, and the IUPAP Young Scientist Prize in Computational Physics all in 2021, an NSF CAREER Award in 2020, being named a Moore Inventor Fellow by the Gordon and Betty Moore Foundation for pioneering innovations in quantum science, CIFAR Azrieli Global Scholar by the Canadian Institute for Advanced Research, a Top Innovator by MIT Tech Review (MIT TR35), and a leading young scientist by the World Economic Forum in 2018. Narang has organized several symposia and workshops relevant to the proposed work, most recently at the APS March Meeting on “Materials for Quantum Information Science”. Her continued service to the community includes chairing the Materials Research Society (MRS) Spring Meeting (2022) and the MRS-Kavli Foundation Future of Materials Workshop: Computational Materials Science (2021), as an Associate Editor at *ACS Nano*, organizing APS, Optica (OSA), and SPIE symposia, and a leadership role in APS’ Division of Materials Physics.

## Tuesday, August 30 | 11:00 a.m. CST

Chen Wang "Towards next-generation physical and logical qubits in superconducting circuits"

**Abstract**: Advances in coherent times and control techniques over the past 20 years have established superconducting circuits as a leading platform for quantum computation. Yet in practice, the performance gap between the current physical qubits (e.g. transmons) and the requirements for known application remains too large to be bridged by the canonical paradigm of fault-tolerant quantum error correction. Fortunately, driven Josephson artificial atoms provides a vast space to tailor qubits and gates in a more protected manner than in two-level systems, which will be crucial for curtailing the QEC overhead and scaling down the error rates.

In this talk, I am going to describe two threads of experiments toward more robust physical and logical building blocks in superconducting circuits. First, we will discuss dissipation engineering as a resource-efficient tool to construct small logical qubits with built-in passive error correction capabilities. This is illustrated by our recent demonstration of autonomous quantum error correction (AQEC) on a Schrodinger cat qubit in a superconducting cavity. Our AQEC is realized by a synthetic dissipation operator powered by continuous-wave drives only, which stabilizes the photon number parity and hence correcting for the dominant single-photon loss errors in the system. Second, we will discuss transition matrix element hierarchy as a framework to design high-fidelity gate operations. This is illustrated by our recent implementation of the two-fluxonium cross-resonance CNOT gate. We show that a low-frequency fluxonium qubit, despite its highly decoupled computational transition, can function as a fast quantum switch for microwave drives using its far-detuned non-computational states.**Bio**: Chen Wang is currently an associate professor in Department of Physics at University of Massachusetts, Amherst. His research focuses on new avenues to protect and to operate superconducting qubits for quantum computing. Chen graduated from Peking University in 2006 with a B.S. in physics and Cornell University in 2012 with a Ph.D. in physics. He worked at Yale as a postdoctoral associate before moving to UMass in 2016. Chen is a recipient of the DOE Early Career Award and Young Investigator awards from AROSR and ARO.

## Tuesday, August 23 | 11:00 a.m. CST

John Nichol "Coherent Spin-Valley Oscillations in Silicon"

Abstract: Electron spins in semiconductor quantum dots are excellent qubits because they have long coherence times and are compatible with advanced semiconductor manufacturing techniques. Coherent manipulation of single electron spins generally involves rapidly oscillating real or effective magnetic fields, which drive magnetic resonance. In this talk, I will describe a new technique for manipulating electron spins in silicon that relies only on dc voltage pulses. This method offers a new way to manipulate electrons in semiconductors and reveals a new family of spin qubits.

Bio: John Nichol is an associate professor in the Department of Physics and Astronomy at the University of Rochester. He earned a PhD from the University of Illinois at Urbana-Champaign and a BA from St. Olaf College. Nichol investigates the quantum mechanics of nanoscale objects, especially individual electrons in semiconductor quantum dots. Nichol's current research focuses on improving the coherence of electron spin qubits using new materials and control methods, exploring new ways to transfer quantum information between distant spin qubits, and many-body quantum coherence in spin chains. Nichol is the recipient of an NSF CAREER award and a Google Research Scholar Award.

**Past Talks - Spring 2022**

## Tuesday, May 3 | 11:00 a.m. CST

Barbara Jones "Simulation of some Open Quantum Systems on Near-term Quantum Computers"

Abstract: Open quantum systems are everywhere in real life, whether it is systems exposed to temperature, electric field, or anything that causes dissipation and/or driving. I will be describing a few such systems that we have simulated on quantum computing hardware, which turns out to be an excellent platform for such simulations. In the first, we use the dissipation naturally occurring in superconducting qubits to map to the heat and relaxation-caused dissipation in an experimental system. This system is one of radical pairs of molecules in solution, caused by excitation of the solution with a radiation burst. The system oscillates between singlet and triplet, with a decay constant at high and low field that we map to that of the quantum computer. We get excellent agreement with experimental results out to many time steps.[1) The second set of hardware experiments were done on a model system, the Hubbard model, in two limiting cases.[2] In the noninteracting, infinite system, we are able to perform 1000 Trotter steps without decay of the measured quantity, a calculation that involved hundreds of CNOT gates. This illustrates the potential for such driven, dissipative system for simulation on a quantum computer. In the second version of the Hubbard model, we go to the opposite limit, and look at the Hubbard ‘atom” in a magnetic field and finite temperature. We are able to calculate quite accurately several physical properties of this system. I will conclude with some remarks about the promise of open quantum systems and of quantum computing in general.

[1] https://arxiv.org/pdf/2001.00794.pdf

[2] https://arxiv.org/pdf/2108.01183.pdf

Bio: Dr. Barbara Jones is currently in the Quantum Applications group at IBM Research Almaden in San Jose, California. Over the years at IBM she has been a manager of both experimental and theoretical groups, working on a number of areas both fundamental and more applied, including magnetic recording heads and media. Since 1997 she has also been a Consulting Professor at Stanford University in Physics and Applied Physics Departments, and supervises Ph.D. students (with two Ph.D.’s granted, and another on the way). Currently her interests are with projects involving theories of quantum interactions in molecular and atomic-scale magnetic systems. She led a team in calculating the unexpected effects of magnetic atoms on metallic/insulating surfaces, as engineered and measured by Scanning Tunneling Microscope.

Her interests of the last few years have been on quantum computing, and she has a paper on theory, and later work has focused on the unique capabilities of current hardware to study open quantum systems, particularly with dissipation.

Dr. Jones is a Fellow of the American Physical Society (APS) and of the American Association for the Advancement of Science (AAAS). She is a recipient of a TWIN Award (Tribute to Women in Industry). She is past Chair of the Physics Section of the AAAS, and a member of the Council of AAAS. She is past Chair of the APS Forum on Industrial Applications of Physics, the largest unit of the APS, as well as of the Chair of the Division of Condensed Matter Physics. She is a member of the committee who wrote the most recent National Academy of Sciences Decadal Survey of Materials, appearing in March 2019, as well as recent past member of the Board on Physics and Astronomy of the National Academy of Science. She also chairs the External Advisory Committee for the National Science Foundation Nanomaterials Center (MRSEC) at Princeton University. She is in addition an Honorary Member of the Aspen Center for Physics.

She also serves on many other science advisory committees, and is organizer of international conferences in the U.S. and Europe.

Chair and Founder of the APS/IBM Research Internships for Undergraduate Women and Under-represented Minorities, member and past Chair of the APS’s Committee on the Status of Women in Physics (1999-2002), and past Chair of the IBM Almaden Diversity Council, she is strongly interested in promoting opportunities in science and math for all students.

## Tuesday, April 19 | 11:00 a.m. CST

Thomas Vidick "Testing quantum systems in the high-complexity regime"

Abstract: From carefully crafted quantum algorithms to information-theoretic security in cryptography, a quantum computer can achieve impressive feats with no classical analogue. Can their correct realization be verified? When the power of the device greatly surpasses that of the user, computationally as well as cryptographically, what means of control remain available to the user? Recent lines of work in quantum cryptography and complexity develop approaches to this question based on the notion of an interactive proof. Generally speaking an interactive proof models any interaction whereby a powerful device aims to convince a restricted user of the validity of an agree-upon statement -- such as that the machine generates perfect random numbers or executes a specific quantum algorithm. Two models have emerged in which large-scale verification has been shown possible: either by placing reasonable computational assumptions on the quantum device, or by requiring that it consists of isolated components across which Bell tests can be performed. In the talk I will discuss recent results on the verification power of interactive proof systems between a quantum device and a classical user, focusing on the certification of quantum randomness from a single device (arXiv:1804.00640) and the verification of arbitrarily complex computations using two devices (arXiv:2001.04383).

Bio: Thomas Vidick is Professor of Computing and Mathematical Sciences at the California Institute of Technology. He received a B.A. in pure mathematics from École Normale Supérieure in Paris, a Masters in Computer Science from Université Paris 7 and a Ph.D. from UC Berkeley. His Ph.D. thesis was awarded the Bernard Friedman memorial prize in applied mathematics. Before joining Caltech he was a postdoctoral associate at the Massachusetts Institute of Technology. His paper “A multi-prover interactive proof for NEXP sound against entangled provers”, with Tsuyoshi Ito, was co-awarded the best paper award at FOCS’12. His is the recipient of a Presidential Early-Career Award (PECASE, 2019), an FSMP research chair (2020) and a Simons Investigator Award (2021-). Vidick's research is situated at the interface of theoretical computer science, quantum information and cryptography. He is interested in applying techniques from computer science, such as complexity theory, to study problems in quantum computing. He is most well-known for his work on the study of entanglement in interactive proof systems, through the complexity class MIP*. He made multiple contributions to quantum cryptography, including the first proof of security of device-independent quantum key distribution. He is also known for developing the first polynomial-time algorithm for computing ground states of gapped one-dimensional quantum spin systems.

## Tuesday, April 12 | 11:00 a.m. CST

John Chiaverini "Techniques and Technologies for Robust Control of Trapped-Ion Quantum Systems"

Abstract: Individual atomic ions manipulated using electromagnetic fields hold promise for practical quantum information processing due to the long coherence times achievable in these natural qubits and the demonstrated capability for high-fidelity quantum logic in multi-ion systems. Trapped ions have been used to perform basic quantum algorithms, but challenges remain in working with arrays of ion qubits while maintaining high fidelity. Among these challenges are the difficulty of robustly addressing many ions using free-space optics and standard electronics. Additionally, photons emitted from ions provide a pathway for remote entanglement generation via the interference of these photons, a method that may be leveraged in future quantum information processors if entanglement can be robustly and quickly established across distributed architectures. Using microfabricated ion-trap chips as a platform for integration, we are developing technologies to potentially overcome these obstacles and enable new scientific and technological explorations.

Biography: John Chiaverini’s research is in the area of trapped-ion quantum information processing, focusing on overcoming challenges to practical quantum computing and sensing through utilization of integrated technologies and novel techniques and encodings. He earned a BS degree from Case Western Reserve University and a PhD degree from Stanford University, both in physics. He did postdoctoral work at the National Institute of Standards and Technology (NIST) in Boulder, CO, where he implemented quantum algorithms in systems of trapped ions, while also developing a novel surface-ion-trap technology. He then took a staff position in the Physics Division at Los Alamos National Laboratory, where he further explored ion-trap integration technologies. Since moving to Lincoln Laboratory, he leads the trapped-ion team and is a Principal Investigator in MIT’s Research Laboratory for Electronics via the MIT Center for Quantum Engineering.

## Tuesday, April 5 | 11:00 a.m. CST

Kejie Fang "Towards single-photon nonlinearity in photonic integrated circuits"

Abstract; Integrated quantum photonic circuits, utilizing weak bulk optical nonlinearities, are typically operated in the parametric regime for quantum light sources and “linear” quantum optical information processing. Realizing single-photon nonlinearity without quantum emitters will be game-changing and enable transcending quantum information capabilities including QND measurement of photons. Based on an integrated photonic platform with a record-high nonlinearity-to-loss ratio and new quantum optical protocols, I will describe our recent work towards this goal. Besides the experiment for photon-photon interaction, the same photonic platform also leads to new means for probing photon-phonon interaction and correlations.

Biography: Kejie Fang received BS in physics from Peking University and PhD in physics from Stanford University. He then worked in Caltech as a postdoctoral researcher. He is now an Assistant Professor in the Department of Electrical and Computer Engineering of University of Illinois at Urbana-Champaign. His research focus is in quantum photonics and optomechanics. He is selected for NSF CAREER Award and DARPA Young Faculty Award.

## Tuesday, March 22 | 11:00 a.m. CST

Anne Broadbent "Bob’s sidekick (or how tripartite quantum correlations satisfy a type of rigidity and how this is useful for cryptography)"

Abstract: We present a variant of the two-prover interactive proof model, where the interaction pattern is limited to a 3-messages: setup-broadcast-response. By virtue of these limitations, classically, the model has the same power as the single-prover model where 3 messages are exchanged. In stark contrast, the quantum version of this model (which we call the ‘Bob’s sidekick’ model) gives rise to monogamy-of-entanglement’ (MoE) games, wherein the limitation on tri-partite entanglement hampers the provers, as compared to the single-prover case. We show how this limitation can be exploited for cryptographic purposes, for instance in “unclonable encryption” where the capacity of an adversary to copy a ciphertext is limited; this is achieved using an MoE game based on conjugate coding. What is more, we show the first rigidity theorem for this MoE game, which means that producing optimal winning statistics strongly constrains the quantum strategy of the provers. From this rigidity result, we derive a weak string erasure protocol, which implies bit commitment — in a model where classical bit commitment is impossible.

Based on joint work with Eric Culf (arXiv:2111.08081) and Sébastien Lord (arXiv:1903.00130).

Bio: Prof. Broadbent is an Associate Professor at the University of Ottawa, Department of Mathematics and Statistics, where she holds the University Research Chair in Quantum Information and Cryptography. She holds a BMath in Combinatorics and Optimization (Waterloo), an MSc and PhD in Computer Science (Montréal) and helds postdoctoral fellowships at the University of Waterloo. Among many awards and accolades, she was awarded the University of Ottawa Young Researcher of the Year Award (2019), the Ontario Early Researcher Award (2016), the André Aisenstadt Prize in Mathematics (2016), the John Charles Polanyi Prize (2010) and the NSERC Doctoral Prize (2009). Prof. Broadbent's research relates to cryptography, communication and information processing in a quantum world.

## Tuesday, March 8 | 11:00 a.m. CST

Chong Zu "Emergent hydrodynamics in a strongly interacting dipolar spin ensemble in diamond"

Abstract: Conventional wisdom holds that macroscopic classical phenomena naturally emerge from microscopic quantum laws. However, building direct connections between these two descriptions has remained an enduring scientific challenge. In particular, it is difficult to quantitatively predict the emergent ‘classical’ properties of a system (for example, diffusivity, viscosity and compressibility) from a generic microscopic quantum Hamiltonian. Here we introduce a hybrid solid-state spin platform in diamond, where the underlying disordered, dipolar quantum Hamiltonian gives rise to the emergence of unconventional spin diffusion at nanometre length scales [1]. In particular, the combination of positional disorder and on-site random fields leads to diffusive dynamics that are Fickian yet non-Gaussian. Finally, by tuning the underlying parameters within the spin Hamiltonian via a combination of static and driven fields, we demonstrate direct control over the emergent spin diffusion coefficient. If time permits, I will end by describing our recent efforts to realize a quantum simulation platform based upon spin defects in 2D [2].

[1] C. Zu, et al., Nature 597, 45-50 (2021)

[2] E. Davis, et al., arXiv:2103.12742 (2021)

Bio: Chong Zu joined Washington University as an assistant professor in the summer of 2021. He received his B.S. in physics and mathematics from Tsinghua University in 2011. After completing his Ph.D. in Prof. Luming Duan’s group at Tsinghua University in 2016, he began postdoctoral work at UC Berkeley in Prof. Norman Yao's group. His research focuses on employing solid-state spin defects (e.g. nitrogen-vacancy centers in diamond) for quantum sensing, simulation and computation.

## Tuesday, March 1 | 11:00 a.m. CST

Jeff Thompson "Quantum computing with neutral Yb atoms"

Abstract: Quantum computing with neutral atoms has progressed rapidly in recent years, combining large system sizes, flexible and dynamic connectivity, and quickly improving gate fidelities. The pioneering work in this field has been implemented using alkali atoms, primarily rubidium and cesium. However, divalent, alkaline-earth-like atoms such as ytterbium offer significant technical advantages. In this talk, I will present our progress on quantum computing using 171-Yb atoms, including high-fidelity imaging, nuclear spin qubits with extremely long coherence times, and two-qubit gates on nuclear spins using Rydberg states [1,2]. I will also discuss several unexpected benefits of alkaline-earth-atoms: an extremely robust and power-efficient local gate addressing scheme [3], and a novel approach to quantum error correction called “erasure conversion”, which has the potential to implement the surface code with a threshold exceeding 4%, using the unique level structure of 171-Yb to convert spontaneous emission events into erasure errors [4]. Time permitting, I will also discuss a new project to implement very high fidelity quantum computing and simulation using circular Rydberg states with 100-second lifetimes [5].

[1] S. Saskin et al, Phys. Rev. Lett. 122, 143002 (2019).

[2] A. P. Burgers et al, arXiv:2110.06902 (2021).

[3] S. Ma, A. P. Burgers, et al, arXiv: 2112.06799 (2021).

[4] Y. Wu, et al: arXiv:2201.03540 (2022).

[5] S. R. Cohen et al, PRX Quantum 2, 030322 (2021).

Bio: Dr. Jeff Thompson is an Associate Professor of Electrical and Computer Engineering at Princeton University. His research explores methods to gain control over individual atoms for computing, communications and sensing technology. In one research direction, he is using nanophotonic circuits to spatially isolate and address individual or small clusters of rare earth ion dopants in crystalline hosts for use as single photon sources and quantum memories. These are crucial ingredients for quantum repeater systems for quantum communications networks. In a second research direction, he is developing techniques to laser-cool and trap large arrays of atoms levitated in vacuum. The potential to create very uniform and homogeneous arrays with long-range photon-mediated interactions creates many possibilities for studies of quantum many-body physics and new quantum computing architectures.

## Tuesday, February 22 | 11:00 a.m. CST

Thomas Faulkner "Beyond the entanglement/minimal surface correspondence"

Abstract: “Entanglement in quantum gravity is famously associated to minimal surfaces - this includes the Bekenstein-Hawking black hole entropy formula where the minimal surface wraps the event horizon. The correspondence suggests entanglement is the basic building block for the emergence of geometry in quantum gravitational theories. Toy models of quantum gravitational states that demonstrate this basic idea can be constructed using random tensor networks. These networks have the same entanglement/minimal surface correspondence. However minimal surfaces give a misleading picture of tripartite entanglement, as shown recently by computations of a novel measure of such entanglement based on reflected entropy. Similarly, minimal surfaces are only a limited probe of the gravitational geometry. We discuss a general picture of reflected entropy in these states and conjecture a relation to multiway cuts, a generalization of a minimal surface with a triple intersection. This suggests that multi-partite entanglement can probe more general geometric structures of quantum gravity.

Bio: Thomas Faulkner is an Associate Professor in the Department of Physics at the University of Illinois Urbana-Champaign. His research group currently works on quantum information aspects of gravity and quantum field theory (QFT). They have uncovered fundamental connections between bounds on the processing of quantum information and the dynamics of quantum gravity and QFT.

## Tuesday, February 15 | 11:00 a.m. CST

Peter Maurer "Quantum Sensing: Probing biological systems in a new light"

Abstract: Quantum optics has had a profound impact on precision measurements, and recently enabled probing various physical quantities, such as magnetic fields and temperature, with nanoscale spatial resolution. In my talk, I will discuss the development and application of novel quantum metrological techniques that enable the study of biological systems in a new regime. I will start with a general introduction to quantum sensing and its applications to nanoscale nuclear magnetic resonance (NMR) spectroscopy. In this context, I will discuss how we can utilize tools from single-molecule biophysics to interface a coherent quantum sensor with individual intact biomolecules, and how this could eventually pave the way towards a new generation of biophysical and diagnostic devices. In a second part, I will discuss a theoretical proposal that utilizes variational techniques to drive a dipolar interacting spin ensemble into a metrological relevant state with Heisenberg limited sensitivity.

Bio: Peter Maurer’s research interests lay at the interface of quantum engineering and biophysics. His lab at the University of Chicago uses quantum technology to develop novel sensing modalities that allow us to probe physical properties of biological systems that are not accessible by conventional technologies. Specific examples of such quantum technology includes a nanoscale magnetic field sensor that enables probing nuclear magnetic resonance spectroscopy at the scale of individual cells and diamond based temperature sensors that provide us with a tool to precisely perturbate biological systems at the nanoscale. Prior to joining the faculty at the University of Chicago, Peter completed a postdoctoral training in Steven Chu’s lab at Stanford University and a PhD in physics at Harvard University.

## Tuesday, February 8 | 11:00 a.m. CST

Jens Koch "Next generation superconducting qubits for quantum computing"

The field of superconducting qubits is currently dominated by the transmon qubit. Over the course of more than a decade, much effort has been devoted to enhancing this circuit's coherence times. Despite the remarkable success, we should ask: is the transmon the best we can do, and will it ultimately suffice for implementing quantum error correction and leaving the NISQ era behind? As I will show, there are interesting circuit alternatives with enhanced intrinsic protection from noise that may well play a decisive role in the future. I will give a tour of some of our recent work on noise-protected qubits such as the zero-pi qubit, and illustrate how our open-source "scqubits" package has made it simpler than ever to explore the world of superconducting qubits.

Bio: Jens Koch is currently an Associate Professor in the Department of Physics & Astronomy at Northwestern University. His current research focuses on the theory, simulations, and advancement of hardware for quantum computing and quantum simulations using superconducting circuits and microwave photons. Koch’s expertise in superconducting qubits and circuit QED reaches back to important contributions to the original theory and development of the transmon and fluxonium qubits. The former currently represents the most widely employed superconducting qubit worldwide. Together with experimental collaborators, Koch’s group now works on the design of novel circuit elements, the development of next-generation quantum circuits with enhanced error protection, and on leveraging quantum optimal control theory for implementing high-fidelity gate operations and quantum-state readout.

## Tuesday, February 1 | 11:00 a.m. CST

Aaron Reinhard "Coherent Control of Processes that Break the Dipole Blockade"

The Rydberg excitation blockade has enabled impressive achievements in quantum information and simulation. However, unwanted processes may compromise the single-excitation behavior of the blockade and reduce its efficiency. We study one such process, state-mixing interactions. When ultracold atoms are excited to Rydberg states near Förster resonance, up to *∼** *50% of the detected atoms can be found in dipole-coupled product states within tens of ns of excitation. There has been disagreement in the literature regarding the mechanism by which this mixing occurs.

We use state-selective field ionization spectroscopy with single-event resolution to probe state mixing near the 43D_{5/2} Förster resonance in Rb. Our method allows us to control the mechanism by which state-mixing interactions occur during Rydberg excitation. Additionally, we use a rotary echo technique to demonstrate the coherence of the evolution of mixed three-particle states during our Rydberg excitation pulses. The ability to coherently control state-mixing events will allow experimenters to avoid this unwanted process when implementing quantum devices using neutral atoms.

Bio: Aaron Reinhard is an experimental atomic physicist studying ultracold Rydberg atoms. His current work focuses on the Rydberg excitation blockade, a key ingredient in neutral atom quantum gates and quantum simulators. With his team of undergraduate student collaborators, he seeks to understand processes that make the single-excitation behavior of the blockade break down. Aaron also does physics education research. He is especially interested in the role of metacognition in promoting expert-like problem-solving behaviors.

Aaron earned a B.S. in physics and a B.S.E.E in electrical engineering from Valparaiso University in 2003, and a Ph.D. in physics from the University of Michigan in 2008. He did a postdoc at Penn State University and has held appointments at Otterbein University and Kenyon College, where he has been an associate professor since 2017.

## Tuesday, January 25 | 11:00 a.m. CST

Luis L. Sánchez-Soto "Achieving the Ultimate Timing Resolution"

Measuring small separations between two optical sources, either in space or in time, constitutes an important metrological challenge. Standard intensity detection fails for vanishing separations, as quantified by the time-honored Rayleigh's criterion. Recently, it has been established that appropriate mode projections can appraise arbitrarily small separations with quantum-limited precision. This has been demonstrated in the lab, both in the spatial and the temporal domain. However, the question of whether the optical coherence brings any metrological advantage to mode projections is still a point of debate. Here, I will discuss this problem and show new experiments putting forwards the effect of varying coherence on estimating the temporal separation between two single-photon pulses.

Bio: Luis L. Sánchez-Soto received his MSc (1984) and PhD in Physics (1988) from the Complutense University of Madrid. He has been visiting researcher at numerous Universities, including Boston, Paris, Stockholm, Munich and Olomouc. He has been a full professor of Quantum Optics in Madrid since 2002. In 2009, he joined the Max Planck Institute for the Science of Light, in Erlangen, where he leads the theoretical group in the Division of Optics and Information. His main research interests are quantum optics and quantum information.

## Tuesday, January 18 | 11:00 a.m. CST

Henry Yuen Cryptography from Pseudorandom Quantum States

Pseudorandom states, introduced by Ji, Liu and Song (Crypto'18), are efficiently-computable quantum states that are computationally indistinguishable from Haar-random states. One-way functions imply the existence of pseudorandom states, but Kretschmer (TQC'20) recently constructed an oracle relative to which there are no one-way functions but pseudorandom states still exist. Motivated by this, we study the intriguing possibility of basing interesting cryptographic tasks on pseudorandom states.

We construct, assuming the existence of pseudorandom state generators, (a) statistically binding and computationally hiding commitments and (b) pseudo one-time encryption schemes. A consequence of (a) is that pseudorandom states are sufficient to construct maliciously secure multiparty computation protocols in the dishonest majority setting. We believe that our results point to an intriguing new landscape of cryptographic protocols and hardness assumptions in the quantum world.

Bio: Dr. Henry Yuen is an Assistant Professor of Computer Science at Columbia University. His research focuses on the interplay between quantum computing, complexity theory, cryptography, and information theory. Yuen received a BA in mathematics from the University of Southern California in 2010, and received his PhD in computer science at MIT in 2016. He was an assistant professor in the Computer Science and Mathematics departments at the University of Toronto between 2018 - 2020, and joined the faculty of Columbia in 2021 .

**Past Talks - Fall 2021**

## Tuesday, November 30 | 11:00 a.m. CST

Ana Asenjo-Garcia Quantum many-body physics with atoms and photons

Tightly packed ordered arrays of atoms exhibit remarkable collective optical properties, as dissipation in the form of photon emission is correlated. In this talk, I will discuss the many-body out-of-equilibrium physics of atomic arrays, and how coherence emerges from dissipation. I will focus on the problem of Dicke superradiance, where a collection of excited atoms synchronizes as they decay, emitting a short and intense pulse of light. Superradiance remains an open problem in extended systems due to the exponential growth of complexity with atom number. I will show that superradiance is a universal phenomenon in ordered arrays, and generically occurs if the inter-atomic distance is small enough. Our predictions can be tested in state of the art experiments with arrays of neutral atoms, molecules, and solid-state emitters and pave the way towards understanding the role of many-body decay in quantum simulation, metrology, and lasing.

Bio: Ana Asenjo-Garcia joined Columbia as an assistant professor of physics in January 2019. Her research focus is on theoretical quantum optics and its intersection with open quantum systems, many-body physics, and quantum information. She graduated from Universidad Complutense de Madrid in 2014. After a short postdoc at the Institute of Photonic Sciences (ICFO) in Barcelona, she joined Caltech as an IQIM Fellow and, later, as a Marie Curie Fellow. She has recently received the Packard Fellowship and the Sloan Fellowship, as well as the NSF CAREER Award and the AFOSR Young Investigator Prize.

## Tuesday, November 16 | 11:00 a.m. CST

Cindy Regal Quantum Optomechanics in Interferometry and Transduction

Over the last decades, quantum effects in vibrations of micromechanical resonators have been observed in a surprising range of experiments. Achieving the quantum regime with tangible motion of solid objects has both piqued the curiosity of physicists, and enabled new approaches to difficult tasks in manipulating quantum information. I will present experiments in our group that measure the motion of micromachined drums, and discuss how they evolved from a rich history of read-out and control in quantum optics and precision measurement. I will highlight our current efforts to use micromechanical motion as a link between quantum states in disparate parts of the electromagnetic spectrum.

## Tuesday, November 9 | 11:00 a.m. CST

Andrew Jordan Quantum Measurement Engines

Abstract: Quantum measurement is usually associated with the gathering of information about a quantum system, and how it collapses the wavefunction. However, the act of measurement also has important physical implications. In this talk, I will discuss how one generally needs to provide energy to measure, and that the energy exchange between the meter and the system can be controlled in order to create a new type of quantum engine. Several examples will be provided.

Biography: Prof. Jordan has physics degrees from Texas A&M and UC Santa Barbara. He was a postdoc at the University of Geneva, with Markus Buttiker, and spend 15 years at the University of Rochester as professor of physics. He recently moved to Chapman University to direct their Institute for Quantum Studies. Areas of interest are in quantum information, quantum measurement, quantum thermodynamics, Foundations of quantum mechanics as well as Quantum Optics and Condensed matter physics. )

## Tuesday, November 2 | 11:00 a.m. CST

Christian Schaffner Local Simultaneous State Discrimination

Abstract: Quantum state discrimination is one of the most fundamental problems studied in quantum information theory. Applications range from channel coding to metrology and cryptography. In this work, we introduce a new variant of this task: Local Simultaneous State Discrimination (LSSD). While previous distributed variants of the discrimination problem always allowed some communication between the parties to come up with a joint answer, the parties in LSSD cannot communicate and have to simultaneously answer correctly. This simultaneity implies, e.g., that the problem does not trivialize for classical states to a non-distributed distinguishing task.

After introducing the problem, we give a number of characterization results. We give examples showing that i) the optimal strategy for local discrimination need not coincide with the optimal strategy for LSSD, even for classical states, ii) an additional entangled resource can increase the optimal success probability in LSSD, and iii) stronger-than-quantum non-signalling resources can allow for a higher success probability in some cases, compared to strategies using entanglement. Finally, we show that finding the optimal strategy in (classical) 3-party LSSD is NP-hard.

While interesting in its own right, this problem also arises in quantum cryptography. In particular, we explore the connections of the problem between unclonable encryption and LSSD. We give an explicit cloning-indistinguishable attack that succeeds with probability 1/2 + μ/16 where μ is related to the largest eigenvalue of the resulting quantum ciphertexts.

Joint work with Christian Majenz, Maris Ozols and Mehrdad Tahmasbi (https://arxiv.org/abs/2103.14510 and another article to appear on arxiv soon)

## Tuesday, October 26 | 11:00 a.m. CST

Danna Freedman Chemically Enabled Atomistic Design of Quantum Systems

Abstract: Chemistry offers a unique approach to quantum information science, whereby we can harness the atomistic precision inherent in synthetic chemistry to create structurally precise, reproducible, and tunable units. Results in this area will be presented, including creating molecules that are analogues of NV centers which we dub molecular color centers. These molecules feature optical read-out of spin information and offer significant promise in the realm of sensing and potentially communication.

Bio: Danna is an F. G. Keyes Professor of Chemistry at MIT. She received her undergraduate degree from Harvard University, and her Ph.D. from the University of California, Berkeley where she studied magnetic anisotropy in molecules. As a postdoc at MIT, she explored two-dimensional magnetism and worked on geometric spin frustration in kagomé lattices and quantum spin liquids. After completing her postdoctoral research at MIT, Danna moved to Northwestern University as an Assistant Professor, where she received tenure. She recently moved to MIT. Her laboratory’s research focuses on applying inorganic chemistry to address challenges in physics.

## Tuesday, October 19 | 11:00 a.m. CST

Christian Schimpf Quantum Communication with Semiconductor Quantum Dots

Semiconductor quantum dots (QDs) are able to confine single charges on the nanoscale in all three dimensions of space, making them excellent systems for exploring quantum phenomena. In particular, QDs have demonstrated outstanding performance as sources of entangled and indistinguishable photon pairs [1,2], properties highly desired in the fields of quantum communication and -information processing. Here I report on the advances of QDs as potential resources for photonic quantum networks, which allow to overcome the fundamental range limitations of single photon-based applications by distributing entanglement over basically unlimited distances [3]. After an introduction to the underlying mechanisms of entangled photon pair generation, I demonstrate several building blocks of quantum networks, such as quantum teleportation [4], entanglement swapping [5] and quantum key distribution [6], and conclude with a perspective towards a real-life quantum-network based entirely on QDs.

[1] D. Huber et al, Nat. Commun. 8, 15506 (2017)

[2] L. Schweickert et al., Appl. Phys. Lett. 112, 093106 (2018)

[3] H. J. Kimble, Nature 453, 1023-1030 (2008)

[4] M. Reindl et al., Sci. Adv. 4, eaau1255 (2018)

[5] F. Basso Basset et al, Phys. Rev. Lett. 16, 160501 (2019)

[6] C. Schimpf et al., Sci. Adv. 7, eabe8905 (2021)

Biography: My academic career started in 2012 with the beginning of my physics studies at the Johannes Kepler University of Linz, Austria. Currently, I am in the later stage of my Ph.D. studies, which I perform as a research associate in the group of Prof. Armando Rastelli, at the institute of semiconductor- and solid-state physics. My research focus lies on semiconductor quantum dots, with emphasis on the generation of non-classical light for quantum optics and applications in the context of quantum communication. My hobbies are coding (games, applications), video games, and sports.

## Tuesday, October 12 | 11:00 a.m. CST

Lindsay LeBlanc Storing and Manipulating Electromagnetic Systems Using Atoms: A Cold-Atom Quantum Memory and a Room-Temperature Atomic Radio

The ability to store and manipulate quantum information encoded in electromagnetic (often optical) signals represents one of the key tasks for quantum communications and computation schemes. In this talk, I will discuss two platforms our group is using to manipulate electromagnetic signals with atoms: With a cold and ultracold atomic systems, we have developed and characterized an efficient and broadband quantum memory that operates in a regime that makes use of Autler-Townes splitting (ATS). We demonstrate on-demand storage and retrieval of both high-power and less-than-one-photon optical signals with total efficiencies up to 30%, using the ground state spin-wave as our storage states. We also realize a number of photonic manipulations, including temporal beamsplitting, frequency conversion, and pulse shaping. In a second, a room-temperature atomic vapour system, we have developed a scheme for radio signal transduction between a microwave and an optical carrier, all mediated through the atoms with the help of a resonant microwave cavity. We are further exploring this promising atomic-vapour + microwave-cavity platform for applications related to optical quantum memory and quantum sensing.

Biography: Lindsay LeBlanc (she/her) is an experimental atomic physicist working with ultracold atoms and quantum technologies. Her current work focuses on both fundamental research and practical applications using atomic physics techniques. With her team, she is currently engaged in three research directions: quantum simulations with ultracold atoms; quantum memories in atomic systems; and hybrid quantum systems, with a focus on microwave interactions and technologies. Lindsay earned her BSc in Engineering Physics from the University of Alberta in 2003 and her Ph.D. in Physics from the University of Toronto in 2011, after which she joined the Joint Quantum Institute in Maryland in 2013 as a postdoctoral fellow, before returning to join the University of Alberta where she is Canada Research Chair in Ultracold Quantum Gases and Associate Professor in Physics.

## Tuesday, September 28 | 11:00 a.m. CST

James Bartusek Quantum Information and Secure Computation

Cryptographic applications of quantum information have been studied since the pioneering work of Wiesner in 1968 and Bennett and Brassard in 1984. In particular, the uncloneable and uncertain nature of quantum information has proven to be useful for achieving various cryptographic tasks, including information-theoretically secure key agreement. This talk will focus on an application of quantum information to the cryptographic notion of secure computation, which allows mutually distrusting parties to jointly compute functionalities over their private inputs. We will discuss the original proposal for “quantum oblivious transfer” due to Crépeau and Killian in 1988, as well as some recent work that establishes its security based solely on the existence of one-way functions.

Biography: James Bartusek is a computer science PhD student in the theory group at UC Berkeley, where he is advised by Sanjam Garg. His research focuses on various aspects of cryptography, including quantum and post-quantum cryptography.

## Tuesday, September 21 | 11:00 a.m. CST

Mankei Tsang Resolving starlight: a quantum perspective

The wave-particle duality of light introduces two fundamental problems to imaging, namely, the diffraction limit and the photon shot noise. Quantum information theory can tackle them both in one holistic formalism: model the light as a quantum object, consider any quantum measurement, and pick the one that gives the best statistics. While Helstrom pioneered the theory half a century ago and first applied it to incoherent imaging, it was not until recently that the approach offered a genuine surprise on the age-old topic by predicting a new class of superior imaging methods. For the resolution of two sub-Rayleigh sources, the new methods have been shown theoretically and experimentally to outperform direct imaging and approach the true quantum limits. Recent efforts to generalize the theory for an arbitrary number of sources suggest that, despite the existence of harsh quantum limits, the quantum-inspired methods can still offer significant improvements over direct imaging for subdiffraction objects, potentially benefiting many applications in astronomy as well as fluorescence microscopy. For a recent review, see https://doi.org/10.1080/00107514.2020.1736375.

## Tuesday, September 14 | 11:00 a.m. CST

John Teufel Listening to the Sound of Entanglement

Quantum mechanics is traditionally considered when measuring at the extreme microscopic scale, i.e. single photons, electrons or atoms. However, even the early pioneers of the quantum theory postulated gedanken experiments in which quantum effects would manifest on an everyday scale. I will present recent experiments in which we engineer and measure microelectromechanical (MEMs) circuits to observe and to exploit quantum behavior at an increasingly macroscopic scale. By embedding mechanical resonators in superconducting microwave circuits, we achieve strong radiation-pressure coupling between fields and motion that allows us to perform quantum experiments of massive objects. I will present our recent experimental demonstration of deterministic macroscopic entanglement, as well as ongoing efforts toward arbitrary quantum control of mechanical systems. The ability to prepare and to “listen” to quantum sound has implications for fundamental science as well as many powerful applications including the processing, storage and networking of quantum information.

## Tuesday, September 7 | 11:00 a.m. CST

**Michael Foss-Feig** Simulating many-body physics using quantum tensor networks

Tensor network techniques exploit the structure of entanglement to dramatically reduce the difficulty of simulating quantum systems on classical computers. But these techniques have limitations, and many problems in many-body quantum physics, for example simulating dynamics, remain intractable despite decades of effort to solve them. Quantum computers offer an alternative route to simulating quantum systems that is in principle efficient, but their small size and limited fidelities have so far prevented solution of problems of real practical interest that cannot be solved classically. Here we discuss prospects for combining these two techniques by directly representing tensor-network states as quantum circuits, and show that recent developments in quantum hardware make it possible to carry out quantitatively accurate simulations of quantum dynamics directly in the thermodynamic (infinite system size) limit using a small number of qubits.

## Tuesday, August 31 | 11:00 a.m. CST

Andrei Faraon Towards optical quantum networks based on rare-earth ions and nano-photonics

Optical quantum networks for distributing entanglement between quantum machines will enable distributed quantum computing, secure communications and new sensing methods. These networks will contain quantum transducers for connecting computing qubits to travelling optical photon qubits, and quantum repeater links for distributing entanglement at long distances. In this talk I discuss implementations of quantum hardware for repeaters and transducers using rare-earth ions, like ytterbium and erbium, exhibiting highly coherent optical and spin transitions in a solid-state environment. We show that single ytterbium ions in nano-photonic resonators are well suited for optically addressable quantum bits with long spin coherence, single shot readout and good optical stability [1]. These single qubits will form the backbone of future quantum repeater networks and will be augmented by optical storage and linear processing capabilities, also implemented using rare-earth ions. Towards this end we demonstrated optical quantum storage using erbium ensembles coupled to silicon photonics, where the frequency and release time of the stored photon can be controlled using on-chip electronics [2,3]. Finally, to connect the optical network to superconducting quantum computers, we develop optical to microwave quantum transducers based on rare-earth ensembles simultaneously coupled to on-chip optical and microwave superconducting resonators [4]. I conclude by addressing the remaining challenges for interconnecting these components into future quantum networks.

[1] Jonathan M. Kindem, Andrei Ruskuc, John G. Bartholomew, Jake Rochman, Yan Qi Huan, Andrei Faraon, Control and single-shot readout of an ion embedded in a nanophotonic cavity, *Nature*, 580, 201–204 (2020)

[2] Craiciu et al, Nanophotonic quantum storage at telecommunications wavelength, *Physical Review Applied*, 12, 024062, 2019

[3] Zhong et al, Nanophotonic rare-earth quantum memory with optically controlled retrieval, *Science*, Vol. 357, Issue 6358, pp. 1392-1395 (2017)

[4] John G. Bartholomew, Jake Rochman, Tian Xie, Jonathan M. Kindem, Andrei Ruskuc, Ioana Craiciu, Mi Lei, Andrei Faraon, On-chip coherent microwave-to-optical transduction mediated by ytterbium in YVO4, *Nature Communications*, 11, Article 3266 (2020)