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. 

Click here for all previous seminar videos

Seminars are organized in collaboration with Mikael Backlund, Jacob Covey, and Dakshita Khurana. 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 -- Spring 2022

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. 

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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 .

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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.

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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. 

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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. ) 

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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) 

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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.

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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. 

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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. 

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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.

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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.

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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.

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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.

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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)

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