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Ultracold Fermi Gas Experimental Group

Quantum gases - collections of atoms cooled to the lowest known temperatures in the universe, have sparked a revolution in atomic physics. Behaviours, usually only found at the microscopic level, become prominent at the macroscopic level. Taking advantage of the precise control and purity available in atomic systems, quantum gases are now being used to address a range of questions in many-body quantum physics.

In the ultracold Fermi gas experimental group we use gases of Li-6 atoms, cooled to temperatures below 100nK, to investigate strongly correlated fermions in the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid of Cooper pairs to a Bose-Einstein condensate (BEC) of molecules. The ability to control the interparticle interactions using Feshbach resonances, as well as the confining potential and dimensionality of the system, enable us to characterise these Fermi systems with unprecedented accuracy.

Our recent work has focussed on (i) measuring excitations and universal properties using Bragg spectroscopy, and, (ii) understanding Fermi gases confined to move in two spatial dimensions. As part of the newly funded ARC Centre of Excellence for Future Low-Energy Electronic Technologies (FLEET) we will test new paradigms for dissipationless transport in topological and non-equilibrium quantum matter synthesised from ultracold atoms.

TWO POSTDOCTORAL POSITIONS AVAILABLE (applications close by 10 July 2017)

We have openings for PhD and Honours students: Please contact Chris Vale directly for more information

The Team

Academic/Research Staff

Chris Vale
Peter Hannaford
Sascha Hoinka
Paul Dyke

 

Students

James Denier (Honours)
Tyson Peppler (PhD)





 

Former Members

Marta Zamorano (intern)
Cécile Carcy (intern)
Dr. Kristian Fenech (PhD)
Dr. Marcus Lingham (PhD)
Alessandro Noccioli (R&D)
Marion Delehaye (intern)
Dr. Eva Kuhnle (PhD) - Bragg Medal
Dr. Gopi Veeravalli (PhD)
Adj. Prof. Bryan Dalton

 

Dr. Wayne Rowlands
Dr. Grainne Duffy (postdoc)
Dr. Jürgen Fuchs (PhD)
Dr. Heath Kitson (PhD)
Dr. David Lau (postdoc)
Dr. Chris Ticknor (postdoc)
Dr. Michael Mark (postoc)
Dr. Michael Vanner (R&D)

Li experimental group images (click to enlarge)

Li Group 2016
2016

Li Group 2012
2012

Li Group 2009
2009

         

Research Highlights

Low-k Bragg Spectra

Goldstone mode and pair breaking excitations

We have mapped out the low-lying excitation spectra of strongly interacting Fermi gases using low-momentum Bragg spectroscopy. Using tightly focussed Bragg beams we directly obtain the speed of sound and pairing gap at near-homogeneous density.

Paper: S. Hoinka et al., Accepted for publication in Nature Physics (2017)

Density EoS

Thermodynamics of a 2D Fermi gas

We experimentally measure the thermodynamic equation of state of a 2D Fermi gas with tunable interactions.

Paper: K. Fenech et al., Phys. Rev. Lett. 116, 045302 (2016), selected for a Viewpoint in Physics

3D to 2D

Criteria for a 2D Fermi gas

Here we measure how increasing the strength of interactions in a 2D Fermi gas leads to a departure from strict 2D behaviour in regimes where an ideal gas would remain kinematically 2D.

Paper: P. Dyke et al., Phys. Rev. A 93, 011603(R) (2016)

Bragg Principle

Review article on Bragg spectroscopy

This paper reviews experiments with Bragg spectroscopy of two-component Fermi gases.

Paper: M. Lingham et al., J. Mod. Opt. 63, 1783 (2016)

Local Response

Local pair condensation

We have developed a technique to obtain local measurements of homogeneous parameters in a harmonically trapped quantum gas and used this to make in situ observations of pair condensation in a unitary Fermi gas.

Paper: M. G. Lingham et al., Phys. Rev. Lett. 112, 100404 (2014)

Contact vs Interaction

Precision measurement of the universal contact

We have made a high precision measurement of Tan's universal contact parameter and compared this with the latest QMC results. Our data have now reached a level of accuracy that allows us to distinguish between several of the established theoretical predictions.

Paper: S. Hoinka et al., Phys. Rev. Lett. 110, 055305 (2013)

Spin Bragg Spectra

Spin Bragg spectroscopy

A new type of Bragg spectroscopy is presented in which we measure the dynamic spin susceptibility of a strongly interacting Fermi gas. This allows independent measurement of the spin-parallel and spin-antiparallel response functions which become universal at high energy.

Paper: S. Hoinka et al., Phys. Rev. Lett. 109, 050403 (2012), arXiv:1203.4657

Contact vs Entropy

Bragg spectroscopic studies of the Contact parameter

Here we present a detailed review of the contact in strongly interacting Fermi gases using Bragg spectroscopy. Both the interaction and temperature dependence are studied and two methods for Bragg spectrocscopy are described.

Paper: E. Kuhnle et al., New J. Phys. 13, 055010 (2011)

Contact vs Temperature

Temperature dependence of the Contact parameter

The contact is a recently introduced parameter to characterise universal properties of strongly interacting quantum gases. In a Fermi gas, the contact depends on the strength of the interparticle interactions and the temperature relative to the Fermi temperature. In this paper we present the first measurements of the temperature dependence of the contact in a unitary Fermi gas.

Paper: E. Kuhnle et al., Phys. Rev. Lett. 106, 170402 (2011)

2D to 3D Crossover

Crossover from 2D to 3D

A weakly interacting Fermi gas is prepared in an oblate trapping potential to study the 2D-3D dimensional crossover. Shell structure, associated with the filling of discrete transverse states becomes apparent in the density profile of the gas.

Paper: P. Dyke et al., Phys. Rev. Lett. 106, 105304 (2011)

Exp vs Theory

Dynamic structure factor (Exp vs Theory)

The dynamic structure factor of a strongly interacting Fermi gas was measured and compared to theoretical calculations based on the Random Phase Approximation (RPA). Surprisingly, these show very good agreement with experimental findings.

Paper: P. Zou et al., Phys. Rev. A 82, 061605(R) (2010)

Static Structure Factor

Universal pairing in a strongly interacting Fermi gas

Pairing in strongly interacting Fermi gases is shown to follow Tan's universal law and is verified through the measurement of the static structure factor using Bragg spectroscopy.

Paper: E. Kuhnle et al., Phys. Rev. Lett. 105, 070402 (2010)

High-k Bragg Spectra

Bragg spectroscopy of a strongly interacting Fermi gas

We have performed a comprehensive study of the Bose-Einstein condensate to Bardeen-Cooper-Schrieffer (BEC-BCS) crossover in fermionic Li-6 using Bragg spectroscopy. A smooth transition from molecular to atomic spectra was observed with a clear signature of pairing at and above unitarity. These spectra probe the dynamic and static structure factors of the gas and provide a direct link to two-body correlations. We have characterised these correlations and measured their density dependence across the broad Feshbach resonance at 834 G.

Paper: G. Veeravalli et al., Phys. Rev. Lett. 101, 250403 (2008), arXiv:0809.2145

Binding Energy

p-wave Feshbach Molecules

We have measured the binding energies of Li-6 p-wave Feshbach molecules using magneto-association spectroscopy. These allow us to determine the magnetic moment of the molecules, and our values are in good agreement with theoretical predictions. We have also investigated the size of p-wave molecules which we find to be much smaller than s-wave molecules even within a few mG of the Feshbach resonance.

Paper: J. Fuchs et al., Phys. Rev. A 77, 053616 (2008)

Molecular BEC

BEC of 6Li2 Molecules

We have produced Bose-Einstein condensates of Li-6 molecules in a low-power crossed optical dipole trap. Our experimental procedures for generating condensates and degenerate Fermi Gases are described in the paper below. More recently we have introduced a 100 W fibre laser to our experiments, now we can produce near pure molecular condensates containing over 200,000 molecules.

Paper: J Fuchs et al., J. Phys. B 40, 4109 (2007)



Grants

ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) (2017-2023)
ARC DECRA, Dr Sascha Hoinka, "Quantum wires of Fermi atoms" (2017-2019)
ARC Discovery Project, "Universal few-to-many-body physics in 2D Fermi gases" (2017-2019)
ARC DECRA, Dr Paul Dyke, "Spin-orbit coupling in a lithium-6 quasi 2D Fermi gas" (2014-2016)
ARC Discovery Project, "Collective dynamics in Fermi superfluids" (2013-2015)
ARC Future Fellowship, A/Prof Chris Vale (2012-2016)
ARC Australian Postdoctoral Fellowship, Dr. Chris Ticknor (2008-2010)
ARC LIEF grant, "Quantum limited single atom detectors" (2008)
ARC LIEF grant, "Advanced microwave facility for quantum atom optics" (2006)
ARC Centre of Excellence for Quantum-Atom Optics (ACQAO) (2003-2010)


Research Podcast
Cold gas research at Swinburne · Video