Wisconsin Quantum Institute

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Events During the Week of February 12th through February 19th, 2023

Monday, February 13th, 2023

The geometry of quantum error correction under biased noise
Time: 11:00 am - 12:00 pm
Place: 5310 Chamberlin Hall
Speaker: Arpit Dua
Abstract: Quantum error correction is necessary because physical qubits have much higher error rates per gate operation than are needed for practical tasks. The popular choice is to encode a logical qubit in a large enough planar layout of many physical qubits, called the surface code, to have sufficiently low logical error rates. The optimal logical error rates depend on the statistical mechanics of logical operators. For example, under biased Pauli noise, having more higher-weight logical operator representations with a higher ratio of low-rate Pauli operators is better. Using this idea, I will discuss how, in active error correction, measuring Clifford-rotated Pauli stabilizers of the surface code can enhance code performance: higher error thresholds and lower subthreshold logical error rates, for biased Pauli noise. Using statistical mechanics and percolation theory, I will describe a phase diagram of 50% thresholds for random Clifford-rotated surface codes under pure dephasing noise. Using tensor network numerics, I will show that certain families of these random codes outperform the best-known translation invariant Clifford-rotated surface codes for finitely biased depolarizing noise.
Host: Thad Walker
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Tuesday, February 14th, 2023

Discovering and Engineering Two-Dimensional Magnetism and Superconductivity
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Tiancheng Song, Princeton
Abstract: Understanding and manipulating macroscopic quantum phenomena such as superconductivity and magnetism are crucial for future quantum science and technology. Two-dimensional (2D) materials and their van der Waals (vdW) heterostructures offer a promising platform to achieve this goal due to their exceptionally broad tunability. In this talk, I will highlight the potential of such a platform through two outstanding examples: 2D magnetism and 2D superconductivity. In the first part, I will talk about a series of emergent phenomena enabled by the vdW nature of 2D magnets, including (1) giant tunneling magnetoresistance enhanced by spin-filtering effects; (2) control of interlayer magnetism by tuning layer stacking; (3) novel moiré magnetism by twisting two layers of 2D magnets. In the second part, I will introduce a new probe to detect superconducting fluctuations down to millikelvin temperatures based on thermoelectric measurements of a monolayer nanoflake. I will discuss surprisingly unusual vortex Nernst signals, which reveal an unconventional superconducting quantum criticality in an electrically tunable 2D superconductor. Finally, I will conclude by highlighting unique opportunities for discovering and engineering new quantum materials and electronic phases in two dimensions.
Host: Victor Brar
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Wednesday, February 15th, 2023

Achieving Practical Computations on Quantum Computers: From Better Qubits to Better Algorithms
Time: 11:00 am - 12:00 pm
Place: 5310 Chamberlin Hall
Speaker: Matthew Otten , Hughes Research Laboratories
Abstract: Quantum information science holds the potential to revolutionize computation, communication, and sensing. Despite recent progress, significant challenges remain to make quantum technology practical and scalable. In this talk, I will highlight my research on simulating open quantum systems, benchmarking quantum devices, and developing efficient quantum algorithms. I will also discuss the physics of different qubits, methods for characterizing and verifying them, and quantum algorithms for chemistry. Finally, I will outline my plans to tackle the remaining challenges and bring practical quantum computing closer to reality.
Host: Thad Walker
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Thursday, February 16th, 2023

No events scheduled

Friday, February 17th, 2023

So a quantum computer walks into the White House…
Time: 3:25 pm - 6:00 pm
Place: 2241 Chamberlin Hall
Speaker: Charles Tahan , Laboratory for Physical Sciences
Abstract: Charle Tahan is Director of the National Quantum Coordination Office (NQCO) within the
White House Office of Science and Technology Policy. Tahan is also
Chief Scientist of the National Security Agency's Laboratory for Physical Sciences.
He got his PhD degree under the supervision of Bob Joynt at UW-Madison.
Host: Robert Joynt
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