Ultracold quantum gases offer a versatile platform to study a wide range of open questions in condensed matter physics and beyond. In particular, their controllability, isolation from noisy thermal environments, and evolution on experimentally-accessible timescales make them a natural choice to probe the effects of driving on time evolution and energy. This thesis details the construction of two cold-atom apparatuses, a lithium machine and a strontium machine, for quantum emulation experiments studying driven systems. Initial numerical simulations along two experimental lines are briefly discussed, and results from the first two experiments on the strontium machine are then presented. In the first, a strontium Bose-Einstein condensate in an optical trap is strongly driven to emulate ultrafast photoionization processes; in a series of proof-of-principle experiments measuring the momenta and energy of particles ejected from the trap, we demonstrate the viability of this technique to study open questions in strong-field physics. The second experiment realizes a tunable quasicrystal, the energy structure for which is described by the multifractal Hofstadter butterfly. Quasiperiodic structures host not only phonons, but also a higher-dimension analogue called phasons. In the experiment, we demonstrate phasonic spectroscopy for the first time by directly driving one of these modes; we characterize the coupling to the resulting excitations, and directly map a slice of the Hofstadter energy spectrum.
Ultracold quantum gases offer a versatile platform to study a wide range of open questions in condensed matter physics and beyond. In particular, their controllability, isolation from noisy thermal environments, and evolution on experimentally-accessible timescales make them a natural choice to probe the effects of driving on time evolution and energy. This thesis details the construction of two cold-atom apparatuses, a lithium machine and a strontium machine, for quantum emulation experiments studying driven systems. Initial numerical simulations along two experimental lines are briefly discussed, and results from the first two experiments on the strontium machine are then presented. In the first, a strontium Bose-Einstein condensate in an optical trap is strongly driven to emulate ultrafast photoionization processes; in a series of proof-of-principle experiments measuring the momenta and energy of particles ejected from the trap, we demonstrate the viability of this technique to study open questions in strong-field physics. The second experiment realizes a tunable quasicrystal, the energy structure for which is described by the multifractal Hofstadter butterfly. Quasiperiodic structures host not only phonons, but also a higher-dimension analogue called phasons. In the experiment, we demonstrate phasonic spectroscopy for the first time by directly driving one of these modes; we characterize the coupling to the resulting excitations, and directly map a slice of the Hofstadter energy spectrum.
Weakly-interacting atoms in a Bose-Einstein condensate coherently occupy the ground-state of their container. This phenomenon, coupled with the technical ability to produce precise, isolated and dynamically-tunable trapping potentials, makes ultracold atoms a versatile platform for simulating quantum mechanical systems. This thesis details the construction of two apparatus at the University of California, Santa Barbara for the production of Bose-Einstein condensates of lithium and strontium atoms respectively. Results of the first experiment performed on the strontium apparatus, a quantum simulation of ultrafast dynamics, are presented. In this experiment, driven cold atoms simulate ultrafast ionization dynamics in attosecond laser pulses, counter-intuitively emulating some of the fastest processes in atomic physics with some of the slowest. A sequence of experiments which demonstrate the correspondence with ultrafast science are described, including the direct observation of carrier-envelope-phase dependent sub-cycle unbinding dynamics. Preliminary results from a second experiment, studying phasonic excitations in a quasiperiodic lattice, are also discussed.
Quantum emulation of extreme non-equilibrium phenomena is a natural application of the precision and control of ultracold atomic physics experiments. In particular, ``Floquet engineering" with an explicitly time-dependent Hamiltonian enables the creation of states of matter that can only exist in the presence of strong driving. In this work, we create and study such tunable strongly driven quantum systems. We use quantum degenerate lithium as a platform because of its light mass, fast tunneling rates, and broadly tunable Feshbach resonance, which allow the study of a wide variety of systems: noninteracting Bosons, strongly interacting many body systems, and bright solitons, to name a few. We describe the experimental setup used to create a 7Li Bose-Einstein condensate as an archetypal quantum platform, and then discuss three key results: the first direct measurement of position-space Bloch oscillations in a cold atom system, the creation of a massive relativistic harmonic oscillator, and finally the demonstration of a new method for controlled long-range quantum coherent transport enabled by Floquet band engineering.
Ultracold quantum gases in optical lattices provide a rich experimental toolbox for simulating the physics of condensed matter systems. With atoms in the lattice playing the role of electrons or Cooper pairs in real materials, it is possible to experimentally realize condensed matter Hamiltonians in a controlled way. To realize the full potential of such quantum simulations, we leverage a quantum gas microscope which can spatially resolve the atoms in the optical lattice at the single site level and project arbitrary potential landscapes onto the atoms by combining the high resolution optics with static holographic masks or a spatial light modulator. The versatility of this system allows for a wide range of studies. In this thesis, we focus on three experiments that highlight the utility of a tunable platform and demonstrate the richness of physics that comes with interactions.\nIn the first, we observe on-site interparticle interactions introduce a non-linearity into the many-body energy spectrum of a harmonic oscillator. The excitation of a single atom into a higher band induces an energy shift in the excitation energy for the second atom, blockading the orbital excitation. We demonstrate a technique for deterministic number filtering based upon orbital excitation blockade. When applied to a high temperature Mott insulator, this number filtering realizes a form of algorithmic cooling, which can be used for initializing a large quantum register or creating low entropy initial states for many-body simulation.\nIn the second, we study the applicability of statistical physics in an isolated system governed by quantum mechanics. While the descriptive power of these two fields has been confirmed through repeated and varied empirical studies, their underlying axioms of entropy maximization and unitary evolution appear mutually exclusive. With our quantum gas microscope, we have the ability to probe local observables such as the on-site number statistics as well as measure the quantum mechanical purity through interference operations. With these capabilities, we are able to observe the local thermalization of a manifestly quantum mechanically pure many-body system.\nIn the last chapter, we report on the first cold atoms studies of an interacting system under an artificial gauge field. We consider the propagation of a pair of atoms in a 2timesN ladder governed by the Harper-Hofstadter model. The eigenstates of this system include both scattering states, which can exhibit chiral propagation, and bound states. A superexchange energy shift in our initial state leads to imbalanced population in the two chiral scattering sectors, leading to chiral propagation dynamics. This effect is the result of both the presence of interactions and the artificial gauge fields. These two components are essential ingredients for fractional quantum Hall physics. Moreover, the dynamic tunable gauge field we develop and the control afforded by a quantum gas microscope make this platform well-suited for future studies in this regime.
Advances in experiments on dilute ultracold atomic gases have given us access to highly tunable quantum systems. In particular, there have been substantial improvements in achieving different kinds of interaction between atoms. As a result, utracold atomic gases oer an ideal platform to simulate many-body phenomena in condensed matter physics, and engineer other novel phenomena that are a result of the exotic interactions produced between atoms. In this dissertation, I present a series of studies that explore the physics of dilute ultracold atomic gases in different settings. In each setting, I explore a different form of the inter-particle interaction. Motivated by experiments which induce artificial spin-orbit coupling for cold fermions, I explore this system in my first project. In this project, I propose a method to perform universal quantum computation using the excitations of interacting spin-orbit coupled fermions, in which effective p-wave interactions lead to the formation of a topological superfluid. Motivated by experiments which explore the physics of exotic interactions between atoms trapped inside optical cavities, I explore this system in a second project. I calculate the phase diagram of lattice bosons trapped in an optical cavity, where the cavity modes mediates effective global range checkerboard interactions between the atoms. I compare this phase diagram with one that was recently measured experimentally. In two other projects, I explore quantum simulation of condensed matter phenomena due to spin-dependent interactions between particles. I propose a method to produce tunable spin-dependent interactions between atoms, using an optical Feshbach resonance. In one project, I use these spin-dependent interactions in an ultracold Bose-Fermi system, and propose a method to produce the Kondo model. I propose an experiment to directly observe the Kondo effect in this system. In another project, I propose using lattice bosons with a large hyperfine spin, which have Feshbach-induced spin-dependent interactions, to produce a quantum dimer model. I propose an experiment to detect the ground state in this system. In a final project, I develop tools to simulate the dynamics of fermionic superfluids in which fermions interact via a short-range interaction.
This thesis highlights the versatility of ultracold atoms as quantum simulators by utilizing Bose gases and engineered light-induced Hamiltonians to investigate quantum phenomena across multiple areas of physics.As a high-energy simulator, an analog experiment simulating particle–antiparticle pair creation from the quantum vacuum, emulated these strong-field effects at energy scales accessible in the laboratory. The Dirac picture of particle-antiparticle vacuum and the concept of optical lattice band theory was the foundation of our approach. In this framework, we readily measured pair creation and demonstrated that this high-field phenomenon is well-characterized by Landau-Zener tunneling. Within condensed matter physics, ultracold atoms were employed to study topological dynamics of periodically driven Floquet systems. Using a Floquet “switching” protocol in a one-dimensional bipartite magnetic lattice, we realized a periodically driven Su–Schrieffer–Heeger model that maps onto a massless Dirac Hamiltonian. By alternating between two lattice configurations with near-optimal timing, we observed spin–momentum–locked transport characterized by well-defined drift velocities and with spatial displacement linearly increasing over many Floquet periods, establishing a platform for exploring topological band dynamics. The culminating focus of this thesis is localization physics in Rb-87 Bose-Einstein condensates subjected to disordered artificial gauge fields over a range of energy and time scales, in both equilibrium and out-of-equilibrium settings. The effective Hamiltonian was implemented by driving two-photon Raman transitions with laser fields, while disordered vector potential landscapes were independently generated using tunable intensity patterns projected by a digital micromirror device (DMD). By varying the experimental protocols—including the turn on times of the Raman coupling and disorder, as well as the disorder strength—we obtained insight into quantum dynamics in the presence of disordered gauge fields. The resulting dynamics revealed rich behavior: including spatially inhomogeneous magnetization for high-energy dynamics and increases in the condensate width after time-of-flight for pulsed disorder in lower energy and near-equilibrium conditions; lastly, signatures of localization, in the form of damped oscillations, were observed as the system was driven out-of-equilibrium.
The extreme tunability and control that atomic physics provides makes quantum gasesideal platforms for experimentally realizing novel synthetic materials beyond what istraditionally realizable in condensed matter experiments. In particular, the ability tocontrol interparticle interactions allows for the realization of long lived nonequilibriumstates, and strong periodic modulation of lattice potentials realizes novel Floquet matter.In this thesis I shall present a series of experiments studying the dynamics of ultracoldlithium in modulated and static one-dimensional optical lattices. First, I present anoverview of the experimental apparatus which includes a description of the generation ofour Bose-Einstein condensate and optical lattices. Then I step through four experimentswhich we conducted. The rst two involve studying spatial dynamics in static opticallattices in the ground and the excited bands which realize position-space Bloch oscillationsand a relativistic harmonic oscillator respectively. The third experiment studies transportin Floquet hybridized optical lattice Bloch bands, and the fourth experiment investigatesprethermalization in strongly modulated lattices with tunable interactions.