Table Of ContentSpringer Theses
Recognizing Outstanding Ph.D. Research
Gauthier Guillaume
Transport and
Turbulence in
Quasi-Uniform
and Versatile
Bose-Einstein
Condensates
Springer Theses
Recognizing Outstanding Ph.D. Research
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Gauthier Guillaume
Transport and Turbulence
in Quasi-Uniform
and Versatile Bose-Einstein
Condensates
Doctoral Thesis accepted by
The University of Queensland, QLD, Australia
123
Author Supervisor
Dr. Gauthier Guillaume Dr. TylerNeely
Schoolof Mathematics andPhysics Schoolof Mathematics andPhysics
TheUniversity of Queensland TheUniversity of Queensland
Brisbane, QLD,Australia Brisbane, QLD,Australia
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-54966-4 ISBN978-3-030-54967-1 (eBook)
https://doi.org/10.1007/978-3-030-54967-1
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Dédié à mes parents pour leur amour et leur
soutien infaillible au cours des années
’
Supervisor s Foreword
Ultracold atoms and Bose-Einstein Condensates (BECs) are nearly ideal experi-
mentalsystemsforinvestigatingawidevarietyofcondensedmatterphysics.Some
oftheseaspectsarisefromthedilutenatureofthesesystems,suchasthesimplicity
of ultracold collisions, for example, but they also arise from the wide variety of
refinedexperimentaltechniquesavailabletotheresearcher.Amongthemorerecent
advanced techniques, the microscopic control of the BEC density and phase using
opticalfieldshasenabledmuchoftherecent experimentalprogressinthefield. Of
particular relevance to this thesis, advanced optical control has yielded new
experiments in quantum turbulence and new developments in the application-
oriented field of atomtronics.
Dr. Gauthier’s thesis foremost develops and demonstrates the application of
directlyimagedDigitalMicromirrorDevices(DMDs)fortrappingandconfiguring
BECs. After first demonstrating the high-resolution DMD pattern projection,
trapping, and imaging of BECs, Dr. Gauthier then develops a feed-forward tech-
nique permitting engineering of both the density and phase of the BEC. These
techniques establish greater control of BECs that will interest readers who seek to
enable future cold atoms experiments with finely structured light. Dr. Gauthier
appliestheseopticaltrappingtechniquestoinvestigatetwoemergingareasoffocus
in superfluid physics: atomtronic oscillators and two-dimensional (2D) quantum
turbulence.
Atomtronics has emerged as a framework for the building of atom devices
analogoustotheirelectricalcounterparts,butwheretheflowofneutralatomstakes
the place of charge carriers. Dr. Gauthier’s thesis demonstrates that for lumped
atomtronics circuits, such as the dumbbell inductor-capacitor (LC) oscillator
investigated,anapproachbasedonacousticsratherthandirectelectronicanalogues
can more accurately predict the behaviour of these superfluid circuits. These
insights will be important to readers who seek approaches for building superfluid
circuit devices, such as inertial sensors.
AmongDr.Gauthier’smostsubstantialresultsaretheobservation,70yearsafter
its prediction, of the vortex cluster states of 2D turbulence that were predicted by
Lars Onsager in 1949. By establishing a uniform quasi-2D condensate, and
vii
viii Supervisor’sForeword
dynamically controlling a DMD to inject vortices, Dr. Gauthier shows that vortex
clusters can persist in 2D superfluids for many seconds. These results demonstrate
that point-vortex equilibria can be observed in superfluids, and such states are
robust even when the entire BEC system is far from equilibrium.
In summary, Dr. Gauthier’s thesis will be of interest to a broad range of the
SpringerThesisaudience. It will beof interest tothose seekinga technical manual
for implementing DMDs and high-resolution optical trapping and imaging of
BECs, or those readers seeking to further develop atomtronic technology and
sensors based on trapped superfluids. It will be offurther interest for those readers
interested in the progress and enabling techniques for the 2D quantum turbulence
research that this thesis pioneers.
Brisbane, Australia Dr. Tyler Neely
June 2020
Abstract
Turbulence,motioncharacterizedbychaoticchangesinpressureandflowvelocity,
isachallengingprobleminphysics.However,itsunderlyingpropertiesarefoundto
beuniversalanddonotdependonthehostfluid.Meanwhile,transportphenomena,
irreversible exchange processes due to the statistical continuous random motion of
particles, although being complicated from a microscopic point of view, can often
be modelled quite simply by tracking macroscopic quantities of interest in the
system.Inthisthesis,usingatomicBose-Einsteincondensates,westudyboththese
phenomena inside a quantum fluid using a highly configurable BEC platform
developed to provide arbitrary dynamic control over the 2D superfluid system.
Furthermore,theexperimentsaremodelledusingtheGross-Pitaevskiiequation,the
point vortex model and the hydrodynamic equations.
Aftertheoreticalbackgroundandintroductiontotheapparatus,thetechniqueof
direct imaging of a digital micromirror device is described, which achieves the
highly versatile and dynamic 2D potentials that facilitate the experimental studies
described. Superfluid transport through a mesoscopic channel of tuneable length
and width is next described. By investigating low amplitude oscillations and their
dependence on the system parameters, a resistor, capacitor, and inductor model is
usedtomodelthetransport.Surprisingly,the“contactinductance”ofthechannelat
the reservoirs is a dominant effect for a significant portion of the parameter range.
The resistive transport for high initial bias is also studied, where we find turbulent
andsounddissipation regimesofenergy dissipationduringthetransport.Next,the
transport between two reservoirs initially prepared at different temperatures, but
with similar particle number, was explored.
Our 2D superfluid system, with hard-wall confinement, provides an ideal
experimentalsystemforthestudyof2Dquantumturbulence.Thesystemisutilized
todemonstratethefirstexperimentalrealizationoflargeOnsagervortexclustersin
the negative absolute temperature regime, through the injection of high energy
clusters into the 2D superfluid. The clusters are found to be surprisingly stable for
longtimeperiods.Thevortexclusterenergylossrateisstudiedwhilechangingthe
system parameters, suggesting thermal damping is the dominant loss mechanism.
ix
x Abstract
Thetechniquesandresultspresented inthis thesis openupnew avenues for the
study of quantum fluids, be it by providing a concise atomtronic model for pre-
dicting superfluid transport or expanding the accessible parameters space available
tofundamentalstudiesofturbulence.Therealizationofnegativetemperaturevortex
distributions,longagopredictedbyOnsager,openuptheexperimentalstudyofthe
full phase-diagram of 2D vortex matter. The refinement of optical trapping tech-
niquesforBECspresentsnewandpromisingdirectionsforfutureBECexperiments
in configured potentials.
