Brand group - Coherent Quantum Gases

Research topics

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 ...

Quantum reflection of solitons Europhys. Lett. 73, 321 (2006) Friction and diffusion of matter-wave solitons Phys. Rev. Lett. 96, 030406 (2006) Soliton generation: Atomic soliton laser Phys. Rev. A. 70, 033607 (2004) Phys. Rev. Lett. 92, 040401 (2004)

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

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

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)