My interests are in the physics of ultracold matter and
quantum gases, and the emergence of macroscopic quantum
phenomena from microscopic quantum mechanics. One of the
themes of my work is to understand aspects of quantum
many-body physics via the interpretation of experimental
data, and I have published several papers with
experimental groups from around the world. I am
particularly interested in nonequilibrium phenomena, both
in weakly and strongly interacting regimes.
Much of my work has been on Bose-Einstein condensates
(BECs), a relatively new state of matter first observed in
1995 (and the discovery of which lead to the Nobel
Prize
in
Physics
in 2001). They form at ultra-cold temperatures
and have similar properties to light from a laser.
However, they are rendered much more complex due to the
fact that atoms are interacting - they undergo
collisions. One intriguing possibility is the
creation of the atom laser, which will be able to be used
in ultra-precise measurement devices.
In 2016 I was
awarded a new ARC Discovery Project in collaboration
withDr Elena
Ostrovskaya, leader of thePolariton BECgroup at
the Australian National University, titled
"Nonequilibrium states of polariton superfluids".
We are currently recruiting a two year postdoctoral
fellow to work on this topic - see the job adverthere, and please
contact me if you need more information. The
project summary is as follows:
"Polaritons are hybrid particles of light
and matter that exist in thin layers of a
semiconductor. At high densities they form a
superfluid, exhibiting quantised whirlpools and
frictionless flow. This proposal aims to design novel
nonequilibrium states of a polariton superfluid, and
to identify why some are more robust than others.
Furthermore, we aim to realise these states in the
laboratory. The project addresses one of the grand
challenges of physics - predicting and controlling the
emergent properties of materials far from equilibrium.
The anticipated outcome is the generation of
fundamental knowledge, which can be used to guide the
design of polaritonic devices in the future."
DP150100100
My other research interests can be roughly divided into
three areas:
"Classical"
dynamics of Bose gases.
One of the major themes of my research has been the
development and application of "c-field" methods for
the dynamics of Bose gases at finite
temperature. This is a non-perturbative
calculation technique that gives access to equilibrium
and non-equilibrium properties of finite
temperature Bose systems. It is valid up
to and above the Bose-Einstein condensation phase
transition, and thus gives the ability to study the
formation of coherence in a BEC. This forms the
basis of my previous ARC QEII Fellowship (2010-14)
entitled "Ebb and flow of superfluids: Bose gases far
from equilibrium."
One of the goals of my QEII fellowship was the study
of quantum turbulence in BEC. Recently I have
developed a scheme to establish non-equilibrium
superfluid flows between reservoirs with different
thermodynamic parameters. This is a very
exciting prospect, as it will allow for the
establishment of non-equilibrium phase diagrams, and I
expect it will be an excellent setup for the study of
turbulence.
Quantum dynamics of
Bose gases
A modification of the "c-field" methods above allows
the simulation of quantum effects in the dynamics of
Bose systems by adding "quantum noise" into the
initial states. This can be used to study
non-linear instabilities and quantum phase transitions
that occur at zero temperature. We have used
this to understand a number of experiments, and have
recently proposed a new experiment to realise a the
"Kibble-Zurek" scaling of the formation of topological
defects in a quantum phase transition in a two
component BEC.
Thermalisation in
isolated quantum systems
In classical systems it is understood that
deterministic chaotic dynamics results in ergodicity
and hence thermalisation following a
disturbance. However, quantum systems evolve
according to linear dynamics. It is understood
that they may thermalise through contact with their
environment, resulting in the loss of information and
resulting in pure states becoming mixed.
However, experiments on ultra-cold gases are in
principle entirely isolated from their
environment. How quantum systems come to thermal
equilibrium through their own dynamics is a major open
question. Significant progress has been made in
this area recently, but there are still many issues to
be solved.
I am looking for students to work
in all of these areas - either for summer, honours,
M.Sc. or Ph.D. projects. Please email me
if
you are interested.
I am currently principal advisor for the
following students:
Chao Feng (PhD, final stages) - Quantum fluctuations
and critical velocity of Bose gases
Jim Mills (PhD, submitted) - Quantum dynamics in a
two component Bose gas
Zhi-Tao Deng (began PhD Q1 2017.)
These PhD students have graduated:
Jan Zill (PhD, 2016) - Nonequilibrium dynamics of a
one-dimensional Bose gas via the coordinate Bethe
ansatz