Theory Group News

CAOUS wins grants

SUT theory group researchers were very successful in 2011, with fellowships and scholarship awards as follows:

Dr Qiongyi He was awarded an Australian Research Council Discovery Early Career Researcher Award. Her topic is:

Creation, detection, and decoherence of a “Schrodinger Cat”.

Dr Laura E. C. Rosales-Zárate was awarded a postdoctoral Fellowship by the Mexican government under the program: “Estancias Postdoctorales y Sabáticas al Extranjero para la Consolidación de Grupos de Investigación. Convocatoria 2011-2012”. Her topic is:

Theoretical study of strongly interacting fermions and fermionic polar molecules in low dimensions.

Rodney Polkinghorne was awarded a Swinburne University Postgraduate Research Award. His topic is:

Simulation of Condensed Gasses by Variation of their Coherent State Expansions.

Adjunct Professor Bryan Dalton has obtained an E. T. S. Walton Visiting Researcher Award funded by the Science Foundation of Ireland to work with Dr Thomas Busch at University College, Cork for six months in 2012. The research topic is:

Atom Interferometry as a Tool for Entanglement Detection.

As part of the program Prof Dalton will give a course of lectures at UC Cork, present seminars at several Irish universities and participate in the UCC public awareness of science program.

VSSUP 2012

The second Victorian Summer School in Ultracold Atomic Physics will be held in Melbourne, Australia over a two week period during the June/July 2012 mid-year break. The School will incorporate approximately 6 lectures per day on current topics in ultracold physics presented by leaders in the field, leaving room for additional tutorials and discussions.

The primary target for this school will be graduate students, although other researchers starting out in this field will also likely find the programme useful.

Novel fermionic superfluidity predicted by SUT theory group

Ultracold atoms have been proven to be an ideal table-top system to reveal novel state of matter. The latest development in ultracold atoms concerns the engineering of a synthetic non-Abelian gauge field [Nature 471, 83 (2011)], which leads to the coupling between spin and orbit degrees of freedom.

Researchers at Swinburne's Centre for Atom-Optics and Ultrafast Spectroscopy have recently predicted a new anisotropic state of matter in spin-orbit coupled ultracold atomic Fermi gases, which consists of exotic quasi-particles with anisotropic effective mass. In the superfluid phase, these exotic quasi-particles exhibit salient features in the momentum distribution, single-particle spectral function and spin structure factor, easily detectable in current experiments. The work has been published in Physical Review Letters.

• Hui Hu, Lei Jiang, Xia-Ji Liu and Han Pu
  Probing Anisotropic Superfluidity in Atomic Fermi Gases with Rashba Spin-Orbit Coupling, Phys. Rev. Lett. 107, 195304 (2011).

Physics mystery solved by SUT theory

In a new paper just accepted by Physical Review A, SUT theorists Shiguo Peng, Xiaji Liu, Hui Hu and Peter Drummond, have solved an outstanding physics mystery. Physicists have searched for a resonant particle-like structure in low dimensional systems of cold atoms, predicted by theorist Maxim Olshanii of University of Southern California. In a mysterious experiment carried out at Innsbruck University, the Austrian experimentalists found many new particle-like resonances - but none corresponding to the predictions. SUT theorists have now explained this.

The new theory predicts resonances quite different to the Olshanii theory. These new anharmonic confinement-induced resonances (ACIR), are unique to the laser-light optical traps used in Innsbruck to channel trapped atoms. The new theory is a nearly perfect fit to the experimental observations. The few remaining unknown resonances are possibly due to multiple ACIR excitations. Shiguo Peng participated in the research while on student exchange from Tsinghua University in Beijing, China, as part of an ARC funded research exchange project.

• Shi-Guo Peng, Hui Hu, Xia-Ji Liu, Peter D.Drummond
  Confinement induced resonances in anharmonic waveguides, arXiv:1107.2725 (to appear in Phys. Rev. A)

SUT Fermion research in the Spotlight

Exact solutions to the three-body quantum challenge, given recently by Swinburne ACQAO theorists Xia-Ji Liu, Hui Hu and Peter Drummond, attracted a Viewpoint commentary in the prestigious online journal Physics [D. Blume, Physics 3, 74 (2010)]. A Viewpoint in Physics spotlights exceptional research published in American Physical Society journals including Physical Review Letters and Physical Review series. So far there are 204 Viewpoint commentaries highlighting important research works in physics, selected from about 40,000 journal publications in the past two years.

The dynamics of three bodies is a famously insoluble classical problem. Despite this, it is completely soluble in quantum mechanics with local interactions, as shown by Liu, Hu and Drummond in their paper in Physical Review B [Phys. Rev. B 82, 054524 (2010)]. These authors give the first complete solution to the problem of three strongly interacting fermions in two dimensions, together with a companion paper in Physical Review A that treats the three dimensional case [Phys. Rev. A 82, 023619 (2010)]. Experimental quantum systems often have more than three particles. For these cases, Liu et. al. show how their three body results can be used to predict static and dynamic properties of many-body systems at high temperatures. This technique is called the quantum virial expansion, and it agrees extremely well with recent ultra-cold atomic experimental measurements in Paris and Melbourne. As well having direct applications to current ultra-cold atomic physics, this work therefore also gives insight into condensed matter physics questions of strongly interacting electrons, including superconductivity, the quantum Hall effect and ferromagnetism.

The Viewpoint commentary describes this work as "an elegant series of papers", a "beautiful contribution that bridges the few-body and many-body worlds", "an important leap", "profound input", "correctly describes the key physics in a quantitative way", "a great deal of insight into the many-body problem".

• D. Blume
  Jumping from two and three particles to infinitely many Physics 3, 74 (2010)

Pseudogap Pairing of a Strongly Correlated Fermi Gas

ACQAO theorists Hui Hu, Xia-Ji Liu, Peter Drummond, and visiting student Hui Dong at Swinburne University of Technology’s Centre for Atom Optics and Ultrafast Spectroscopy (CAOUS) have recently developed a new theoretical tool to elucidate the controversial pseudogap pairing in strongly correlated atomic Fermi gases.

This new theoretical framework is motivated by a series of experiments at JILA (Colorado, USA), MIT (USA), Tokyo University (Japan) and SUT (Australia). All of these experiments focus on investigating the dynamical response of strongly-interacting ultra-cold Fermi gases to external fields. In this way, experimentalists have probed the dynamical structure of strongly correlated Fermi gases, to obtain information about mechanisms of pairing. Such questions have immediate relevance not just to ultra-cold atomic physics. They also help in the scientific understanding of other strongly interacting Fermi gases - from high-Tc superconductors to neutron stars - where there is a need to quantitatively decide which theoretical models are best.

This theoretical work is vitally important because, for the first time in this field, it was shown how to apply a high-temperature virial expansion to dynamical problems in this exciting research on ultra-cold Fermi gases. Such virial expansions have exceptional significance because they are free of the usual problem of unjustified theoretical approximations. In the past, this led to a plethora of competing theories, without any clear way to distinguish them. Instead, by the use of high temperature expansions, theorists are now able to make use of a small parameter, namely the inverse temperature. This still allows one to investigate the topical problem of pseudogap pairing above the critical point, and is an important step towards more extended use of this method.

This research shows an excellent agreement with recent experiments, where other methods have failed to obtain good agreement.

• H. Hu, X.-J. Liu, P.D. Drummond, and H. Dong,
  Pseudogap Pairing in Ultracold Fermi Atoms, Phys. Rev. Lett. 104, 240407 (2010).

Top French laboratory confirms SUT prediction

France's top physics lab, Ecole Normale Superieure in Paris, has published a new experimental study of ultra-cold atoms, one of the "hottest" fields of modern physics. Their paper published in Nature this month confirms a theoretical prediction made by Swinburne physicists. The SUT calculation, by Liu, Hu, and Drummond, worked out the equations describing a new form of matter. Outside of the laboratory, this new form of matter, a universal Fermi gas, is only found inside neutron stars.

Swinburne physicists, using a novel theoretical approach, predicted a new value for the virial coefficient used to describe the universal gas. The predicted value was completely different from previous theories, even having the opposite sign. The first experiment in the world was carried out by Christoph Salomon last year, in Paris. The requirements for the experiment were to cool millions of atoms of lithium metal to a billionth of the temperature of outer space.

The novel SUT theory was developed last year with funding from the Australian Research Council. It used exact mathematical solutions for one of the hardest problems in physics: the three-body quantum bound state. The results of the experiment matched theoretical predictions to the last measured decimal. The French laboratory's independent and careful experimental work at the frontiers of physics completely justifies the new theoretical approach developed in Australia.

Understanding such cold temperatures is an advance in pure science today. Tomorrow's technology will be built on these types of development, as the physics of ultra-cold atoms is applied to new generations of quantum sensors and simulators.

• X.-J. Liu, H. Hu and P.D. Drummond,
  Virial expansion for a strongly correlated Fermi gas, Phys. Rev. Lett. 102, 160401 (2009);
• S. Nascimbcne, N. Navon, K. J. Jiang, F. Chevy and C. Salomon,
  Exploring the thermodynamics of a universal Fermi gas, Nature 463, 1057 (2010).

EPR: From Concepts to Applications

EPR entanglement is one of the fundamental mysteries of the quantum world, since it was proposed by Einstein, Podolsky and Rosen in 1935. Today, entanglement is the key building block of any quantum technology, and measures to quantify entanglement are an important tool. An international team of experts, led by Margaret Reid and Peter Drummond from ACQAO have provided a comprehensive review of our ability to generate and measure EPR entanglement. This overview has now appeared in Review of Modern Physics.

Digital quantum memories: storing Schroedinger's cat

Developing axons use Bayes-optimal strategy to follow subtle chemical gradients

The neutron star on your table-top

Dr Margaret Reid has been elected a Fellow of the Optical Society of America

Prof. Peter Drummond awarded the Moyal Medal and Lecturer for 2007

ACQAO members successful in the ARC grants

Strongly Interacting Polarized Fermi Gases

Universal Behavior in Strongly Interacting Fermions

Extension of Einstein's work

2004 Massey Medal awarded to Peter Drummond

Launch of the book "Quantum Squeezing"

Nobel Prize-winner confirms UQ physics theory

Love and Hate Between Atoms on a Wire