Wisconsin Quantum Institute

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Events During the Week of February 6th through February 13th, 2022

Monday, February 7th, 2022

No events scheduled

Tuesday, February 8th, 2022

Novel optical probes in the study of condensed matter systems
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Ilya Esterlis, Harvard University
Abstract: A great deal of our understanding of condensed matter comes from observing how materials interact with light. In recent years, the development of novel optical probes has opened yet a new route by which to investigate condensed matter systems, allowing to both interrogate interesting materials that are challenging to study by conventional means and also yielding information in complementary parameter regimes. I will focus on two such probes: exciton spectroscopy in 2D semiconductors and sensing with nitrogen-vacancy (NV) centers in diamond. As a concrete demonstration, I will describe (1) how these probes have been utilized to establish the existence of Wigner crystal phases — the solid phase of the interacting electron gas — in 2D transition-metal dichalcogenide (TMD) systems and (2) how they may further elucidate properties of the electron solid and also shed light on the nature of the corresponding liquid-solid transition, where effects such as frustrated magnetism and impurity interactions are expected to result in exotic and fascinating physics. Finally, I will provide some outlook on the promise of these techniques to investigate more general classes of interesting condensed matter systems.
Host: Robert McDermott
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IQUIST seminar: "Next generation superconducting qubits for quantum computing"
Time: 11:00 am
Speaker: Jens Koch, Northwestern University
Abstract: 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.
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Wednesday, February 9th, 2022

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Thursday, February 10th, 2022

NISQ: Error Correction, Mitigation, and Noise Simulation
Time: 10:00 am
Place: virtual:
Speaker: Bei Zeng, The Hong Kong University of Science and Technology
Abstract: Error-correcting codes were invented to correct errors on noisy communication channels. Quantum error correction (QEC), however, may have a wider range of uses, including information transmission, quantum simulation/computation, and fault-tolerance. These invite us to rethink QEC, in particular, about the role that quantum physics plays in terms of encoding and decoding. The fact that many quantum algorithms, especially near-term hybrid quantum-classical algorithms, only use limited types of local measurements on quantum states, leads to various new techniques called Quantum Error Mitigation (QEM). This work addresses the differences and connections between QEC and QEM, by examining different application scenarios. We demonstrate that QEM protocols, which aim to recover the output density matrix, from a quantum circuit do not always preserve important quantum resources, such as entanglement with another party. We then discuss the implications of noise invertibility on the task of error mitigation, and give an explicit construction called quasi-inverse for non-invertible noise, which is trace-preserving while the Moore-Penrose pseudoinverse may not be. We also study the consequences of erroneously characterizing the noise channels, and derive conditions when a QEM protocol can reduce the noise. virtual:
Host: Mark Saffman
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Friday, February 11th, 2022

No events scheduled