Seminar

Chemistry Seminar Series – Steve Winter, Wake Forest University

Host: A. Wei Tsen

Quantum materials represent a broad class of systems whose experimental response relies directly on entanglement between their underlying degrees of freedom. Modeling of such materials presents a variety of challenges related to a disparate variety of complex behaviours that manifest at different energy scales, and a typical sensitivity of responses to model parameters. In this field, first-principles approaches often provide a vital bridge between experiments and theoretical models. In this talk, I will introduce our numerical strategies for systematically building low-energy models with local charge, spin, and orbital degrees of freedom of arbitrary complexity. I will discuss the insights that these methods have yielded for frustrated magnetic insulators collectively known as "Kitaev materials", which have prompted a recent explosion of interest in quantum magnets where spin-orbit coupling induces strongly anisotropic and competing magnetic interactions. I will specifically address our recent attempts to understand the magnetic models of few-layer RuCl3 and high-spin d7 Co(II) compounds, which have recently been identified as possible alternative platforms for realising the celebrated Kitaev model.

IQC Seminar featuring Ali Assem Mahoud

This talk aims to highlight some mathematical tools that can be used in prob- lems related to quantum computing. We start with monogamy-of-entanglement games and study how to approach them through the Haar measure on unitary matrices. ...

ZOOM online Seminar Featuring Ahmad Farooq, Ph.D. - Kyung Hee University

Reliable and efficient reconstruction of the quantum states under the processing of noisy measurement data is a vital tool in fundamental and applied quantum information sciences owing to communication, sensing, and computing. Noisy intermediate-scale quantum (NISQ) computers are expected to perform tasks that surpass the capability of the most powerful classical computers available today. ...

IQC Seminar featuring Dr. Stephen Vintskevich

There are multiple challenging issues one must address to boost further the nascent field of quantum technologies. The most common are reducing noises’ affection on a given quantum protocol’s performance, performing well-controlled quantum operations, and developing general frameworks for mapping various practical problems into quantum algorithms performed in different quantum devices. ...

Measuring quantum fields with particle detectors and machine learning

Abstract: The model for measurements used in quantum mechanics (based on the projection postulate) cannot be extended to model measurements of quantum fields, since they are incompatible with relativity. We will see that measurements performed with particle detectors (i.e., localized non-relativistic quantum systems that couple covariantly to quantum fields) are consistent with relativity, and that they allow us to build a consistent measurement theory for QFT. For this measurement framework to be of practical use, we need to understand how can we measure specific properties of the field using a particle detector. I will show that there is a simple fixed measurement protocol that allows us to extract essentially all the information about the field that the detector gathers, and that this information can then be interpreted to study a specific targeted feature using machine learning techniques. Specifically, I will examine two examples in which we use a neural network to extract global information about the field (boundary conditions and temperature) performing local measurements, taking advantage of the fact that this global information is stored locally by the field, albeit in a scrambled way.

Seminar featuring Giampiero Marchegiani - Technology Innovation Institute, Abu Dhabi

Single-particle excitations, known as Bogoliubov quasiparticles, threaten the operation of superconducting qubits. In this presentation, we theoretically revisit and generalize the qubit-quasiparticle interaction, including the gap asymmetry in Josephson junctions, which naturally arises from the deposition of aluminum layers with different thicknesses. ...

IQC Seminar featuring Michael Wilke, McGill University

The pioneering experiments by Hanbury and Twiss are considered by many as the beginnings of experimental quantum optics. These experiments are now particularly relevant in the context of quantum photonics and the characterization of single photon sources.
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Professor Anthony Leggett - University of Illinois

One of the historically earliest proposals for implementing the idea of (partially) protected topological quantum computing involves the physical braiding of the Majorana fermions believed to exist in two-dimensional Fermi superfluids in which the order parameter has the so-called chiral ("p+ip") symmetry. (For many years a plausible candidate system was single-plane strontium ruthenate, but recent experiments have somewhat muddied the waters). The original theoretical paper on this topic (Ivanov 2001), and most of the subsequent literature on it, uses the Bogoliubov-de Gennes equations, thereby violating the principle of conservation of total particle number. In this informal talk I will report on some work with Yiruo Lin* which inter alia attempts to examine how far the standard conclusions continue to hold when we insist on conserving particle number.

The ability to engineer the electrical, optical and magnetic properties of advanced materials on the nanoscale is of increasing importance to the development of future technologies. One approach to achieving this is through impurity doping, with increased control over the spatial resolution and isotopic purity enabled by the development of dedicated tools. In this talk the 'P-NAME' tool will be described, and the underlying principle surrounding its application for the development of doped systems for quantum technologies including qubits presented. cont.

Quantum Chaos in Kicked Top

Quantum-classical correspondence is of fundamental interest as it allows for computing and analysing the quantum properties with respect to their classical counterparts. This helps us study the transition from the quantum to the classical. According to the correspondence principle, quantum mechanics should agree with classical mechanics in appropriate limits. In our first project, we show that currently available NISQ computers can be used for versatile quantum simulations of chaotic systems. We introduce a classical-quantum hybrid approach for exploring the dynamics of the chaotic quantum kicked top (QKT) on a  universal quantum computer. The programmability of this approach allows us to experimentally explore the complete range of QKT chaoticity parameter regimes inaccessible to previous studies. Furthermore, the number of gates in our simulation does not increase with the number of kicks, thus making it possible to study the QKT evolution for arbitrary number of kicks without fidelity loss. Using a publicly accessible NISQ computer (IBMQ), we observe periodicities in the evolution of the 2-qubit QKT, as well as signatures of chaos in the time-averaged 2-qubit entanglement. We also demonstrate a connection between entanglement and delocalization in the 2-qubit QKT, confirming theoretical predictions. However, the connection between classical and quantum mechanics is not straightforward, especially in chaotic systems. The question of why a chaotic system, in certain situations, breaks the correspondence principle remains one of the open questions. Nevertheless, the breaking of Quantum classical correspondence for a large system i.e., the large value of j (but finite), is surprising. It suggests that the system never behaves classically in certain situations, irrespective of the system size. It is also worth exploring this strange behavior from an experimental point of view, as it will decide the parameters of the experimental setup designed for studying Quantum Chaos.