title: EXPERIMENTAL STUDIES OF MEAN-FIELD BOSE-EINSTEIN CONDENSATES AND BEYOND
title: JOSEPHSON PHYSICS, QUANTUM SCATTERING, AND A ZEEMAN LATTICE
titleType: Subtitle
Creators: name: Mukhopadhyay, Annesh
Publisher: name: Washington State University
Year: 2024
Subjects: Bose-Einstein condensate
Gross- Pitaevskii equation
Josephson junction
Mean field dynamics
Optical lattice
Spin-orbit coupling
Atomic Physics

description: Quantum gases at temperatures near absolute zero are powerful testbeds for probing complex dynamics connected to open questions in many areas of modern physics, including quantum optics, quantum information, or condensed matter physics. The research provided in this thesis utilizes dilute gas Bose-Einstein condensate to gain fundamental insights into quantum dynamics. It motivates new device paradigms for quantum technologies with applications to quantum sensing, quantum analog simulation, and quantum metrology.
description: The first study in this thesis describes the supercurrent flow between weakly coupled Bose-Einstein condensates (BECs) at two discrete momentum states, demonstrating the momentum space Josephson effect. Experimental observation of this exotic phenomenon is done using a BEC with Raman-induced spin-orbit coupling, where the tunneling between two local band minima is implemented by the momentum kick of an additional optical lattice. A sudden quench of the Raman detuning induces coherent spin-momentum oscillations of the BEC, which is analogous to the a.c. Josephson effect. Both plasma and regular Josephson oscillations are observed in different parameter regimes. The experimental results agree well with the theoretical model and numerical simulation
description: and showcase the important role of nonlinear interactions. The measurement of the Josephson plasma frequency also gives the Bogoliubov zero quasimomentum gap, which determines the mass of the corresponding pseudo-Goldstone mode, a long-sought phenomenon in particle physics. The observation of momentum space Josephson physics offers an exciting platform for quantum simulation and sensing utilizing momentum states as a synthetic degree.
description: In the second study, a combined experimental and theoretical investigation of quantum mechanical scattering between atoms in a dilute-gas Bose-Einstein condensate is presented. Condensates with sufficiently high densities are prepared such that a very rich sequence of multiple scattering events has to be taken into account. A superposition of two different momentum states is prepared, and the resulting scattering effects are imaged in time-of-flight imaging. Scattering between particles in different spin states is also studied using the Raman-induced spin-orbit coupling. The experiments are accompanied by theoretical studies that develop a model taking scattering cascades into account. A surprising complexity of the dynamics is revealed even in conceptually simple experimental configurations.
description: In the final study, dynamics in a Zeeman lattice structure emerging from the simultaneous application of Raman and radio frequency coupling to a dilute-gas Bose-Einstein condensate is investigated. Periodic band structures are a hallmark phenomenon of condensed matter physics. While often imposed by external potentials, periodicity can also arise through the interplay of couplings that are not necessarily spatially periodic on their own. The role of Galilean invariance in this system is studied. The Zeeman lattice is characterized by various techniques, including Bloch oscillations and lattice shaking with spin and momentum-resolved measurements. This combined coupling scheme allows for exceptional tunability and control, enabling future investigations into
description: unconventional band structures such as quasi-flat ground bands and those with semimetal-like band gaps.