Session D03: Jin Award for Best Ph.D. Thesis

Emulating gravity with linear and nonlinear optical settings.

A century passed since Einstein published the theory of General Relativity (GR), and some predictions of GR still elude observation. Hence, analogous systems, such as optical systems, have been suggested as emulation platforms. GR is inherently nonlinear: for example, masses dynamics is affected by the curved space they themselves induce. However, thus far all GR optical emulation demonstrated linear dynamics, where fix curved background determines the evolution of the electromagnetic (EM) waves. We demonstrate analogous gravitational effects with optical wavepackets under a long-range thermal nonlinearity. This optical system is mathematically equivalent to the Newton-Schrodinger model, which has been studied strictly theoretically, and describe a mass density evolving according to the Schrodinger equation in the presence of a gravitational potential created by the mass density itself. These wavepackets interact by the curved space they themselves induce, exhibiting complex nonlinear dynamics arising from the interplay between diffraction and the emulated gravity. We observe emulated gravitational lensing, tidal forces and gravitational redshift in this system, including modification of these phenomena that rise due to the nonlinear nature of gravity which exists in the Newton-Schrodinger model. Finally, we exploit the properties of EM fields in curved space, to present a new class of nanophotonic structures which facilitate control over the evolution of light, through the space curvature of the medium within which the light is propagating. This general method of fabricating curved-space structures for controlling electromagnetic waves can serve as the basis for curved nanophotonics: a generic concept for controlling EM waves that can be employed in integrated complex photonic circuits.   

Quantum many-body dynamics with driven Bose condensates: Kibble-Zurek mechanism and Bose fireworks

In recent years, ultracold atomic gases have provided a platform for stunning advancements in the study of quantum many-body dynamics. My thesis focuses on developing paradigmatic experimental examples, from which we can derive universal principles connecting many far-from-equilibrium, quantum many-body systems; in this talk, I will focus on two key studies. First, I will present our study of the dynamics of bosons undergoing a quantum phase transition in a shaken optical lattice. The dynamics are almost completely independent of the rate at which the transition is crossed, exhibiting a space-time scaling symmetry which can be understood using the universal Kibble-Zurek mechanism. Second, I will discuss our serendipitous discovery of ``Bose fireworks'': the sudden emission of many bright, narrow jets of atoms from Bose-Einstein condensates with oscillating interaction strength. This structure arises from collective, inelastic collisions in the condensate, which are seeded by quantum fluctuations and then strongly stimulated in a manner analogous to superradiant systems. I will also briefly discuss our new scheme for spatiotemporally modulating the interactions between atoms. I will conclude by exploring the exciting future prospects for each of these efforts. \footnote{This thesis work was supervised by Professor Cheng Chin at the University of Chicago}   

New Tools for Precision Measurement and Quantum Science with Narrow Linewidth Optical Transitions

I will present a set of tools that rely on narrow linewidth optical transitions to extend the capabilities of precision measurement and quantum science. The focus of this work has been the development of an experimental system in which large ensembles of strontium atoms are coupled to an optical cavity by narrow-linewidth optical transitions. This has enabled the first explorations of optical superradiance on such transitions, with the goal of creating a highly precise active optical frequency reference. Key results include first characterizations of superradiance from narrow (7.5 kHz) and ultranarrow (1 mHz) linewidth optical transitions, observations of interesting spin-exchange dynamics in the lasing system, and an assessment of the frequency stability of the superradiant light. Aside from superradiance, other projects from my thesis work include a demonstration of nondestructive atom counting using a narrow-linewidth transition, a fundamentally new form of laser cooling applicable to narrow-linewidth transitions, and extensions to proposed methods for using atoms to detect gravitational waves.   

Quantum Gas Microscopy of Fermionic $^{40}$K

In the past decade, ultracold atoms have emerged as a pristine platform for quantum simulation of strongly correlated systems. One prototypical model is the Fermi-Hubbard model, a simple yet hard-to-solve Hamiltonian believed to capture aspects of high-$T_c$ cuprates. In recent years, quantum gas microscopy (QGM) has made possible detection and control of single atoms within large ensembles, enabling novel studies of many-body systems. Although QGM of bosonic atoms had been pioneered in 2009, microscopy of fermionic atoms proved to be more challenging, requiring development of new imaging techniques. In this talk, I will describe how we perform QGM on fermionic $^{40}$K, and some experiments that we have performed. Using our microscope, we have directly observed metals, band and Mott insulators. The site-resolving ability of QGM has also allowed measurement of spin and charge correlations. This has revealed the antiferromagnetic nature of spins and the bunching of doublons near half-filling, and anti-bunching of singlons at low fillings due to Pauli-blocking. With progress towards lower temperatures and novel studies on non-equilibrium dynamics, QGM experiments can potentially shed light on various mechanisms that are at work in strongly correlated systems.