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Wednesday, April 5, 2023 12:00 pm - 1:00 pm EDT (GMT -04:00)

IQC Student Seminar Featuring Xi Dai

Landau-Zener tunneling: from weak to strong environment coupling

Abstract:

Landau-Zener tunneling, which describes the transitions in a two-level system during the passage through an anti-crossing, is a model applicable to a wide range of physical phenomena. Dissipation due to coupling between the system and the environment is an important factor in determining the transition rates. Using a superconducting tunable capacitively shunted flux qubit, we observe the crossover from weak to strong coupling to the environment. The weak coupling limit corresponds to small system-environment coupling and leads to environment-induced thermalization. In the strong coupling limit, environmental polarizations dress the system and transitions occur between the dressed states. Our results confirm previous theoretical studies of dissipative Landau-Zener tunneling in the weak and strong coupling limits, and motivate further work on understanding the intermediate regime. This work is relevant for understanding the role of open system effects in quantum annealing, where Landau-Zener transitions at small gaps, occurring in large scale systems, are important to understand for improving the success probability.

 

This talk is based on the preprint arXiv:2207.02017.

Thursday, April 6, 2023 3:00 pm - 4:00 pm EDT (GMT -04:00)

Collusion Resistant Copy-Protection for Watermarkable Functionalities

CS/Math Seminar - Jiahui Liu (UT Austin)

Copy-protection is the task of encoding a program into a quantum state to prevent illegal duplications. A line of recent works studied copy-protection schemes under ``1 -> 2 attacks'': the adversary receiving one program copy can not produce two valid copies. However, under most circumstances, vendors need to sell more than one copy of a program and still ensure that no duplicates can be generated. In this work, we initiate the study of collusion resistant copy-protection in the plain model. Our results are twofold:

Monday, April 10, 2023 10:30 am - 11:30 am EDT (GMT -04:00)

Accelerating Quantum Dynamics With Long-Range Interactions

IQC Special Seminar - Jeremy Young - JILA, University of Colorado

One of the major goals in the field of quantum science is to utilize the properties of quantum mechanics for applications in quantum computation, quantum simulation, and quantum sensing. In order to address this goal, a variety of different many-body quantum platforms have been developed. Many of these quantum platforms exhibit long-range interactions, particularly power-law interactions, including Rydberg atoms, polar molecules, and trapped ions, among others. This gives rise to a natural question: how does the long-range nature of these interactions affect the resulting quantum evolution? 
 

Tuesday, April 11, 2023 3:30 pm - 5:00 pm EDT (GMT -04:00)

Bystander Training

IQC will be hosting a training session open to current IQC staff, faculty and research assistant professors.

Bystander Intervention can help create a sense of belonging, care, and respect within our communities. The Sexual Violence Prevention & Response Office (SVPRO) is conducting training across the UWaterloo campus to provide skills and resources to help people intervene when they see a harmful, or potentially harmful, situation.  

 

Debanjan Chowdhury: The good, the bad and the strange: Unconventional metallic behaviour in the vicinity of Mott insulators

Abstract: In recent years, we have witnessed remarkable experimental breakthroughs in uncovering the intriguing properties of correlated metals in the vicinity of Mott transitions. Describing these phenomena theoretically remains an open challenge. This talk will focus on three recent examples of puzzling electronic behavior near Mott insulating phases and address the various conundrums. In the first part of the talk, I will discuss the microscopic origin of an unconventional T-linear resistivity with Planckian scattering in a quasi-two-dimensional “good” metal with long mean-free path, consisting of highly conducting metallic and Mott insulating layers, respectively. In the second part, I will address the origin of a low-temperature “bad” metallic behavior in the vicinity of a continuous bandwidth-tuned metal-insulator transition in a moiré semiconductor. I will end by presenting some new theoretical insights into the experimental observation of an anomalous particle-hole continuum and overdamped plasmon in the density response of cuprate “strange” metals. 

Wednesday, April 12, 2023 2:30 pm - 3:30 pm EDT (GMT -04:00)

Millimeter-Wave Optomechanical Circuits for Preparing Non-Gaussian States of Motion

IQC Special Seminar - Bradley Hauer, National Institute of Standards and Technology

In the current paradigm of quantum cavity optomechanics, the relatively weak parametric coupling between an electromagnetic cavity and a mechanical resonator is mediated by an external pump. While this strong cavity drive acts to enhance the optomechanical interaction, it obscures its intrinsic nonlinearity, restricting these systems to bilinear operations on Gaussian states. By increasing this coupling such that it dominates the decoherence rates of the system, one could instead use the fundamental optomechanical nonlinearity to prepare the mechanical resonator into complex, non-Gaussian states...

Friday, April 14, 2023 2:00 pm - 2:45 pm EDT (GMT -04:00)

Exploring by the Seat of Your Pants: Experiments in the Quantum Realm

Quantum mechanics helps us understand what happens below what a microscope can see, describing the world of atoms, electrons, photons, and more. In celebration of World Quantum Day on April 14th, Dr. John Donohue from the Institute for Quantum Computing will sit down with Exploring by the Seat of Your Pants to explore quantum science and its applications, from light particles and electron waves to superconductors and quantum computers.

Wednesday, April 19, 2023 12:00 pm - 1:00 pm EDT (GMT -04:00)

IQC Student Seminar featuring Andrew Jena

AEQuO: A Comprehensive Measurement Allocation Protocol

Abstract: The variational quantum eigensolver (VQE) is a hybrid quantum-classical algorithm for solving the electronic structure problem, a problem foundational to the field of computational chemistry. In the VQE, a classical optimizer directs the state preparation protocol while a quantum device is used to measure the expectation value of the Hamiltonian with the prepared state. We developed the adaptive estimation of quantum observables (AEQuO) protocol in an attempt to use all of information from the measurement outcomes to minimize the number of measurements needed. I will give an overview of the VQE and the techniques we employ in our protocol, and I will discuss where our approach fits in with the previous measurement allocation techniques.