Spring 2023

Abstract: Atom interferometers can be used to obtain information about accelerations and fields, whether this may be in the investigation of fundamental aspects of physics, such as measuring fundamental constants or testing gravity, or as part of a measurement device, such as an accelerometer [1,2,3]. Achieving adequate coherence times remains a priority, and this can be realized by holding the atoms in a trap as an alternative to increasing their free fall time [1].

Abstract: Superconductivity in the limit of a vanishing bandwidth in isolated bands is a classic example of a non-perturbative problem, where BCS theory does not apply. What sets the superconducting phase stiffness, and relatedly the transition temperature, in this limit is of both fundamental and practical interest. This question has become especially relevant with the discovery of superconductivity in moiré materials.

Abstract: Over the past decade, advances in atomic, molecular, and optical (AMO) physics techniques enabled the cooling of simple molecules down to the ultracold regime (< 1 mK), allowing unprecedented control over their quantum states. This opened a host of new opportunities in quantum information, precision measurement, and controlled chemistry. I will discuss two experiments on precisely probing and controlling inter- and intramolecular dynamics at ultralow temperatures, respectively.

Pizza and drinks will be served after the talk

Abstract: A quantum state that depends on a parameter is a commonly studied structure in quantum physics. Examples include the ground state of a Hamiltonian with a parameter or Bloch states as functions of the quasimomentum. The change in the state as the parameter varies can be characterized by such geometric objects as the Berry phase or the quantum distance which has led to many insights in the understanding of quantum systems.

Abstract: Quantum pseudorandom states are efficiently constructable states which nevertheless masquerade as Haar-random states to poly-time observers. First defined by Ji, Liu and Song, such states have found a number of applications ranging from cryptography to the AdS/CFT correspondence. A fundamental question is exactly how much entanglement is required to create such states. Haar-random states, as well as t-designs for t≥2, exhibit near-maximal entanglement.

Abstract: 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.

Pizza and drinks will be served after the seminar

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.

Abstract: 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. Another possibility is to optically probe the 2DCG, which provides the advantage of more local measurements.