CTCP
Centre for Theoretical Chemistry and Physics
at Massey University (Albany Campus), New Zealand





Brand group - Coherent Quantum Gases

The coherent quantum gases group is interested in various aspects of the physics of ultracold atomic gases. Of particular interest are nonlinear wave phenomena (solitons) and strong correlations in the Bose and Fermi quantum gases.

Principal Investigator: Prof. Joachim Brand
Brand group
From left to right: Prof. Joachim Brand, Dr. Oleksandr Fialko, Sophie Shamailov, Jayson Cosme

Not in picture:
Peter Jeszinszki
Dr. Lauri Toikka

Previous group members
Dr. Shreyoshi Gosh
Dr. Antonio Muñoz Mateo
Alex Ayet
Dr. Alberto Cetoli
Gabriele Jaritz
Dr. Renyan Liao
Dr. Thomas Ernst
Dr. David Hallwood
Jake Gulliksen
Marie-Coralie Delattre
Musical vibration patterns inspire the search for defects in ultra-cold atomic gase

Similar to musical instruments, superfluid defects can resonate at characteristic frequencies that produce intriguing patterns.

The explanation of this phenomenon goes back to the eighteenth century, when Ernst Chladni observed grains of sand assemble in geometric patterns on the surface of a plate excited to characteristic tones with a bow. The lines of sand that we nowadays call Chladni figures trace the nodal lines of vibration modes. In a similar fashion to Chladni`s plates, a standing wave in a confined superfluid called dark soliton possesses characteristic vibration modes with geometric patterns of nodal lines. Being unstable vibrations, the dark soliton decays leaving behind a skeleton of vortex lines that make up solitary waves themselves. The two simplest structures, a single vortex line called solitonic vortex, and a vortex ring have already been observed in quantum gases. However, solitonic vortices and vortex rings are just two members of a whole family of standing waves, the Chladni solitons.

Stability and dispersion relations of three-dimensional solitary waves in trapped Bose-Einstein condensates
A. Muñoz Mateo, J. Brand
New J. Phys. 17, 125013 (2015)

Chladni solitons and the onset of the snaking instability for dark solitons in confined superfluids
A. Muñoz Mateo, J. Brand
Phys. Rev. Lett. 113, 255302 (2014)

Chladni solitons and Chladni plates
Chladni solitons made of vortex lines in a superfluid (above) versus Chladni figures made of nodal lines of plate vibrations (below). Central image from William Henry Stone, Elementary Lessons on Sound (Macmillan and Co., London, 1879), p. 26, fig. 12; and side images from Chladni, E. F. F., Entdeckungen ueber die Theorie des Klanges (Weidmanns Erben und Reich, 1787).

Research topics

Solitons in Bose-Einstein Condensates

Particle and Wave Nature of Matter-Wave Bright Solitons

Bose-Einstein condensate with attractive interactions can form non-spreading wavepackts, a sort of self-cohesive drops also called bright solitons. Being a special sort of nonlinear waves, bright solitons share many properties of classical particles. However, depending on the circumstances they may still reveal their quantum nature. Read more about ...

Soliton interacting with thermal gas

Soliton and vortex ring ring collisions

Solitons and vortex rings are examples of nonlinear wave phenomena, which maintain their shape during propagation. The collisions of such waves were recently observed in a Bose-Einstein condensate for the first time. The experiment at Harvard University showed evidence of unexpected shell-like structures. Simulations give evidence that these structures are hybride objects composed of soliton fronts and vortex rings.

Phys. Rev. Lett. 95, 110401 (2005)
Phys. Rev. Lett. 94, 040403 (2005)

Story on Physics News Update
Article for Physik in unserer Zeit
Complex hybrid structures

Solitonic vortices and the snake instability

What happens to vortices when they are put into a narrow channel? What is the 1D analog of a vortex? We study the effects of transverse confinement on vortices in a repulsive, elongated BEC. In a regime where the width of the elongated trap is about 6 to 12 healing lengths, vortices show properties usually associated with solitons. In particular, their velocity may be associated with a characteristic phase step and collision properties are soliton-like. Thus we speak of solitonic vortices. A connection can be made to the snake instability of soliton stripes which is also a mechanism that may be exploited to experimentally create solitonic vortices [1 ]. A different way of producing solitonic vortices in a controlled manner is stirring in a toroidal trap [2 ]. Properties are studied using 2 and 3D simulations of the Gross-Pitaevskii equation but also using the method of image charges which yields an exactly solvable model of vortex dynamics.

[1] Phys. Rev. A 65 (2002) 04361
[2]J. Phys. B: At. Mol. Opt. Phys. 34 (2001) L113-L119

Svortex generated by transverse instability

Strongly-Interacting Quantum Gases

We are interested in the many-body theory of quantum gases under the influence of strong correlations. In particular there are interesting crossover scenarios for a Bose gas in one dimension or a two-component Fermi gas under the influence of a Feshbach resonance.

Is the 1D Bose gas superfluid?

The 1D Bose gas at zero temperature has many surprising properties that are very distinct from 3D Bose-Einstein condensates including the loss of phase coherence and a fermionic excitation spectrum with appearance of two branches of elementary excitations. According to the Landau criterion of superfluidity this should prevent the possibility of superfluidity. However, according to common definitions of condensed-matter physics, the superfluid fraction of the interacting 1D Bose is known to be 100%. In order to really understand the superfluid properties of the 1D Bose gas we calculate the dynamic structure factor and the drag force that a heavy but small particle feels when dragged through the gas. Check back on this page to read our upcoming preprint when it is ready or read our previous papers on the 1D Bose gas:

Phys. Rev. A 73, 023612 (2006)
Phys. Rev. A. 72, 033619 (2005)
Phys. Rev. A. 70, 043622 (2004)
J. Phys. B: At. Mol. Opt. Phys. 37 (2004) S287-S300

Levinson's theorem for atomic scattering on Bose-Einstein condensates

Levinson's theorem of potential scattering connects the number of bound states of a given potential to the phase shifts of scattering solutions. Excitations of a weakly interacting Bose condensate are described by the coupled Bogoliubov equations. Scattering solutions for a finite trapping potential describe the scattering of single, identical particles. Can Levinson's theorem be generalized and the number of bound collective excitations of a condensate be linked with the phase shifts of single-particle scattering? Particularly interesting situations occur for kinks or vortices in shallow traps as they can give rise to 'bound states in the continuum' of single particle scattering.

Phys. Rev. Lett. 91, 070403 (2003)

Maintained by Peter Schwerdtfeger | Last updated: January, 2015 | Copyright 2014 | Massey University