Probing Non-Equilibrium Dynamics in Two-Dimensional Quantum Gases (Springer Theses)

✍ Scribed by Cheng-An Chen

• Publisher: Springer
• Year: 2022
• Tongue: English
• Leaves: 151
• Category: Library

✦ Synopsis

This thesis explores the physics of non-equilibrium quantum dynamics in homogeneous two-dimensional (2D) quantum gases. Ultracold quantum gases driven out of equilibrium have been prominent platforms for studying quantum many-body physics. However, probing non-equilibrium dynamics in conventionally trapped, inhomogeneous atomic quantum gases has been a challenging task because coexisting mass transport and spreading of quantum correlations often complicate experimental analyses. In this work, the author solves this technical hurdle by producing ultracold cesium atoms in a quasi-2D optical box potential. The exquisite optical trap allows one to remove density inhomogeneity in a degenerate quantum gas and control its dimensionality. The author also details the development of a high-resolution, in situ imaging technique to monitor the evolution of collective excitations and quantum transport down to atomic shot-noise, and at the length scale of elementary collective excitations. Meanwhile, tunable Feshbach resonances in ultracold cesium atoms permit precise and dynamical control of interactions with high temporal and even spatial resolutions. By employing these state-of-the-art techniques, the author performed interaction quenches to control the generation and evolution of quasiparticles in quantum gases, presenting the first direct measurement of quantum entanglement between interaction quench generated quasiparticle pairs in an atomic superfluid. Quenching to attractive interactions, this work shows stimulated emission of quasiparticles, leading to amplified density waves and fragmentation, forming 2D matter-wave Townes solitons that were previously considered impossible to form in equilibrium due to their instability. This thesis unveils a set of scale-invariant and universal quench dynamics and provides unprecedented tools to explore quantum entanglement transport in a homogenous quantum gas.

✦ Table of Contents

Supervisor's Foreword
Acknowledgments
Journal Articles Published as a Result of This Thesis Research
Contents
1 Introduction
1.1 Toward Designer Quantum Simulator
1.2 Two-Dimensional Homogeneous Bose Gases
1.3 Feshbach Resonance
1.3.1 s-Wave Scattering
1.3.2 Feshbach Resonances in Cold Collisions
1.3.3 Optical Feshbach Tuning
1.4 Weakly Interacting Bose Gases
1.4.1 Bogoliubov Theory
1.4.2 Quasiparticle Correlation
1.4.2.1 Structure Factor
References
2 Experimental Setup
2.1 Laser System
2.1.1 External-Cavity Diode Laser
2.1.1.1 Reference Laser
2.1.1.2 Cooling Laser
2.1.1.3 Repumper Laser
2.1.2 Tapered Amplifier
2.1.3 dRSC Laser
2.1.4 Nd:YAG Laser
2.1.5 Ti:Sapphire Laser
2.2 Magnetic Coil
2.2.1 Main Coil
2.2.2 Bias Coil
2.3 Vacuum System
2.3.1 Design
2.3.2 Preparation
2.4 Computer Control
References
3 Experimental Procedure
3.1 Production of Bose–Einstein Condensate
3.1.1 Laser Cooling
3.1.1.1 Zeeman Slower
3.1.1.2 Magneto-Optical Trap
3.1.1.3 Compressed MOT and Optical Molasses
3.1.1.4 Degenerate Raman Sideband Cooling
3.1.2 Evaporative Cooling
3.2 Production of Two-Dimensional Quantum Gas
3.3 Spatiotemporal Optical Control
3.3.1 Spatial Control
3.3.2 Temporal Control
3.4 Optical Lattices
References
4 Universal Quench Dynamics and Townes Soliton Formation
4.1 Introduction
4.2 Methods
4.3 Results
4.4 Conclusion
References
5 Scale-Invariant Townes Solitons
5.1 Introduction
5.2 Methods
5.3 Results
5.4 Conclusion
References
6 Quasiparticle Pair-Production and Quantum Entanglement
6.1 Introduction
6.2 Methods
6.3 Results
6.4 Conclusion
References
7 A Compact and Versatile Quantum Gas Machine
7.1 Introduction
7.2 Methods
7.3 Other Upgrades
7.4 Conclusion
References
8 Summary
8.1 Review of Past Work
8.2 Outlook and Future Work
8.2.1 Optical Feshbach Tuning
8.2.2 Phononic Crystal
8.2.3 Acoustic Black Hole
References
A Cesium Feshbach Resonances
B Zeeman Slower Detail
C Main Coil Detail
D Optical Feshbach Tuning
References
E Appendix for Universal Quench Dynamics and Townes Soliton Formation
E.1 Formation of a Townes Soliton Array
E.2 Quench-Induced Dynamics in the Density Power Spectrum
E.2.1 Theory of Density Structure Factor After an Interaction Quench to Attractive
E.2.2 Amplification of Density Waves from Density Fluctuations Prior to the Quench
E.2.3 The Scaling Behavior
E.2.4 Relationship with Quench Dynamics at Repulsive
E.2.5 Experimental Test of the Scaling Behavior in the Density Power Spectrum
E.3 Soliton Collision Dynamics
E.3.1 Soliton Binary Collision Rate
E.3.2 Collision Lifetime of Solitons
E.4 Collapse and Expansion Dynamics of an Unstable Townes Soliton
E.4.1 Second Interaction Quench
E.4.2 Fitting Atom Number Loss During Rapid Soliton Collapse
References
F Appendix for Scale-Invariant Townes Solitons
F.1 Magnetic Two-Body Interaction Tuning
F.2 Scale-Invariant 2D Solitons
F.3 Effect of the MDDI on 2D Scale Invariance
F.3.1 Scale Invariance in Deep 2D Limit
F.4 Quasi-Scale Invariance
References
G Appendix for Quasiparticle Pair-Production and Quantum Entanglement
G.1 Calibration of the Density Noise Power Spectrum
G.2 Separability Criterion
References