The cold atom toolbox in momentum space

An, Fangzhao Alex

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https://hdl.handle.net/2142/108417 Copy

Description

Title

The cold atom toolbox in momentum space

Author(s)

An, Fangzhao Alex

Issue Date

2020-05-29

Director of Research (if dissertation) or Advisor (if thesis)

Gadway, Bryce

Doctoral Committee Chair(s)

DeMarco, Brian

Committee Member(s)

• Eckstein, James N
• Bradlyn, Barry

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• physics
• amo
• atomic
• molecular
• optical
• quantum
• gas
• gases
• bose
• einstein
• condensate
• Bose--Einstein condensate
• BEC
• momentum-space
• lattice
• momentum
• space
• topology
• disorder
• interactions
• quantum simulation
• Hall
• effect
• chiral
• current
• edge
• state
• synthetic
• gauge
• field
• flux
• transport
• Aubry
• Andre
• zigzag
• Bragg
• spectroscopy
• loss
• non-Hermitian
• optics
• mobility edge
• mobility
• wavepacket
• Josephson
• junction
• array
• quasiperiodic
• pseudodisorder
• potassium
• rubidium
• self-trapping
• Bloch oscillation
• current-phase relation

Abstract

"The many weird properties of quantum mechanics at the very small scale have led to surprising and useful discoveries that manifest at the macroscopic level, like the quantum Hall effect and high temperature superconductivity. Yet trying to understand the origin of correlated behavior from interacting quantum systems via classical simulation requires an infeasible level of computing power. Instead, we can use an easily tunable, clean quantum system as a quantum simulation of a more unwieldy system, building the same model to study the same physics, but in a more controlled environment. Our field of cold neutral atoms in optical lattices has seen success over many years as a platform for quantum simulation of various lattice models from condensed matter physics. The recent (2015) implementation of lattices not in position, but in a synthetic dimension by coupling individual quantum states with lasers has led to a more bottom-up approach to engineering lattice models. In this thesis, we present our ""momentum-space lattice"" technique in which we use individual laser frequencies to couple the momentum states of a rubidium-87 Bose-Einstein condensate, in order to create lattices with site-by-site and link-by-link precision. This technique is simple to implement experimentally, requiring just two additional common optical components (acousto-optic modulators) compared to a real-space lattice, yet is incredibly versatile. Using momentum-space lattices, we have studied the physics of artificial magnetic fields, disorder and pseudodisorder-induced localization, and atomic interactions across eight works described in this thesis. More interesting are the not-so-well-known effects that arise in the interplay among these three components of topology, disorder, and interactions, and we have made headway towards studying physics in this regime. To be more specific, in our studies we have generated an artificial magnetic field for neutral atoms, and directly observed the resulting chiral currents in both a square ladder and zigzag lattice geometry. We have further monitored the quantum walk behavior of atoms under disordered and pseudodisordered lattices, observing a transition to localization under a quasiperiodic potential. We have been able to introduce a tunable energy dependence to this localization transition (single-particle mobility edge) in two ways: with the addition of more tunneling pathways, and by modifying the form of the potential. Finally, we have studied the effects of nonlinear inter-atomic interactions in the momentum-space lattice, observing self-trapping in a double well system as well as on a full lattice, showing a skewed current-phase relationship in an analog to Josephson junction arrays, and investigating an interaction-induced shift in localization behavior under pseudodisorder. In constructing the momentum-space lattice apparatus, Eric, Bryce, and I have created a promising new platform for Hamiltonian engineering. The studies described here not only show off the capabilities of the technique, but also realize new models, reveal new physics, and provide a new perspective complementary to both real-space lattice techniques and real materials. We have observed topological edge states more directly than previous works and engineered precise lattice parameter variations unavailable to other techniques, and yet the best is still to come. With our ongoing experimental upgrades comes access to the regime of strong inter-particle interactions, which promises more challenging yet more rewarding experiments."

Graduation Semester

2020-08

Type of Resource

Thesis

Permalink

http://hdl.handle.net/2142/108417

Copyright and License Information

Copyright 2020 by Fangzhao Alex An. All rights reserved.

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