Spring 2023

Large machine learning models are revolutionary technologies of artificial intelligence whose bottlenecks include huge computational expenses, power, and time used both in the pre-training and fine-tuning process. Based on quantum Carleman linearization and shadow tomography (QRAM is not necessary), we design the first quantum algorithm for training classical sparse neural networks with end-to-end settings.

In this seminar, I will present and discuss recent results from one of the experimental research lines at Hafezi group: quantum Hall physics in semiconductor microcavities. A 2D charge gas (2DCG) operating in the quantum Hall regime represents one of the few examples of macroscopic quantum behavior. Other examples in this short list are Bose-Einstein condensation and superconductivity. Typically, the experimental study of the quantum Hall effect relies on transport.

Obtaining real-time dynamics of particle collisions is a long-standing goal in high energy and nuclear physics. Developing protocols to simulate lattice gauge theories on quantum simulators offer a strategy to probe these scattering processes. Both long-range and short-range quantum Ising chains exhibit the confinement of quasiparticles, analogous to the high-energy confinement of quarks in bound, meson states. In this talk, we will discuss a proposal to simulate meson scattering in a trapped-ion simulator.

Abstract: Superconducting circuits are an attractive system for forming qubits in a quantum computer because of the natural energy gap to excitations in the superconductor. However, experimentally it is observed that superconducting qubits have excitations above the superconducting ground state, known as quasiparticles, at a density that is many orders of magnitude above the expected equilibrium level.

Intermediate-scale quantum devices are becoming more reliable, and may soon be harnessed to solve useful computational tasks. At the same time, common classical methods used to verify their computational output become intractable due to their prohibitive scaling of required resources with system size. In this talk, I aim at giving an overview of selected verification strategies. Inspired by recent experimental progress, we analyze efficient cross-platform verification protocols for quantum states and computations.

The spectral form factor is an important diagnostic of quantum chaos and thermalization. In this talk we will dive into a surprising duality between short time behavior and exponentially late-time behavior, with a cameo from the Riemann zeta function.

(Pizza and refreshments will be served after the talk.)

Abstract: Ultracold-atom quantum simulators are powerful experimental tools that provide insight into the properties of crystalline solids. Important crystalline solid properties, such as electrical resistivity and optical absorption, are set by the crystal’s energy band structure (bands of the allowable energies of electrons in the potential generated by a lattice arrangement of atomic or molecular ions). However, it is not only the band structure that determines the properties of a crystal.

Abstract: In this talk, I will describe two distinct strategies for trapping Majorana zero modes (MZMs) with superconducting vortices. There exists a common belief that for s-wave superconductors, the existence of normal-state band topology, such as the topological Dirac surface state, is crucial for inducing vortex MZMs. We recently uncovered a striking example where nontrivial vortex Majorana physics arises in a trivial s-wave superconductor with a trivial normal state.

Abstract: Over the last decade, flat optical elements composed of an array of deep-subwavelength dielectric or metallic nanostructures of nanoscale thicknesses – referred to as metasurfaces – have revolutionized the field of optics. Because of their ability to impart an arbitrary phase, polarization or amplitude modulation to an optical wavefront as well as perform multiple optical transformations simultaneously on the incoming light, they promise to replace traditional bulk optics in applications requiring compactness, integration and/or multiplexing.

Correlations are fundamental in describing many body systems. However, in experiments, correlations are notoriously difficult to assess on the microscopic scale, especially for electron spins. While it is firmly established theoretically that the electrons in a Cooper pair of a superconductor form maximally spin-entangled singlet states with opposite spin projections, no spin correlation experiments have been demonstrated so far.