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Title:Properties of dirty bosons in disordered optical lattices
Author(s):Ray, Ushnish
Director of Research:Ceperley, David
Doctoral Committee Chair(s):Leggett, Anthony
Doctoral Committee Member(s):DeMarco, Brian; Kwiat, Paul
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Dirty Bosons
Disordered Systems
Disordered Bose-Hubbard Model
Quantum Monte-Carlo
Disordered Superfluids
Abstract:The study of the disordered Bose-Hubbard model is key to understanding the interplay of disorder and interactions. Despite many studies with uniform diagonal disorder, few have inquired into experimental realizations with an additional correlated off-diagonal disorder. The presence of a trap and finite temperature effects in experiments lead to multiple do- mains of the Superfluid, Mott-Insulator/normal and the Bose-Glass phase. Previous studies using approximate theories produced results that are not in accordance with experiments. Stochastic Series Expansion is a finite temperature technique that can solve Bosonic lattice Hamiltonians exactly for large systems. Here, studies are performed for an extensive range of parameters using disorder distributions that are similar to experiments. Insights are first acquired by studying trap-free situations. Constant density calculations show that, although the qualitative features of the phase diagram remain robust between speckle disorder and uniform box disorder, there are quantitative differences. Studies of the Bose-glass phase ex- plicitly show that it is composed of superfluid puddles that are stable to finite temperature effects for large temperature ranges. Finite temperature behavior of a strongly correlated sys- tem reveals that at unit filling, the transition temperature of the superfluid is increased due to the addition of disorder. Inquires are then extended to discern the properties of trapped systems. Extensive calculations show that domain-like structures that develop can be rig- orously demarcated using the single-particle eigenstates extracted from the single-particle density matrix. Observables are calculated for the system at the single-site and global scales, showing that intermediate length scales provide the correct description of the physics of the domains in these systems. These techniques are used to conclusively show the possibility of the re-entrant superfluid that should be accessible to experiments. The temperature de- pendence of the re-entrant domain is explicitly calculated to be within experimental limits provided interactions are not too large. Comparisons with the local density approximation show reasonable agreement at low disorder strengths. At large disorder strengths there can be quantitative errors and can also result in qualitative errors. The phase diagram due to speckle disorder is presented for a range of values that are readily accessible to experiments. It is quantitatively shown that the effects of off-diagonal disorder are minimal. The superfluid remains unaffected despite large disorder in the tunneling term. Full scale ab initio calcu- lations of the largest trapped disordered systems to date are performed in order to identify the superfluid-Bose-glass phase boundary in collaboration with experiments. Results show remarkable agreement, but there are open questions with regards to the possibility of glassy dynamics.
Issue Date:2015-04-22
Rights Information:Copyright 2015 Ushnish Ray
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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