Super Tonks Girardeau gas
We observe a novel, excited quantum many-body phase called the Super Tonks-Girardeau gas with strong attractive interactions  . Usually, strongly attractive quantum gases are expected to form dense particle clusters and to loose their gas-like properties. But in 2005, it was proposed in  that there is a many-body state of attractively interacting bosons in one-dimensional systems that does not decay. If prepared in a special way, this lowest gas-like state is stable and exhibits new quantum mechanical properties.
The figure above is a sketch of possible many-body states of three attractively interacting atoms in 1D. A full calculation can be found in . Attractive atoms in the ground state form a cluster with all atoms clumped together. Adding energy to the system allows to excite single atoms to form hybrid states or to excite all atoms to gas like states. The energetically lowest gas like state is called the Super Tonks-Girardeau gas. Atoms in this state are strongly correlated and show long range order with a Luttinger Liquid parameter K<1 . Since each particle occupies a certain volume, the gas properties are similar to a classical gas of hard rods.
To prepare the Super Tonks-Girardeau phase it is necessary to increase the repulsive interaction strength all the way through the Tonks-Girardeau regime up to infinity. Sudden switching from infinitely strong repulsive to infinitely attractive interactions stabilizes the gas against collapse and connects the ground state of the Tonks gas to the excited state of the Super Tonks gas. We switch interactions by means of a novel type of scattering resonance in 1D systems.
Confinement-Induced Resonances in 1D systems
Most many-body effects change drastically with the number of spatial dimensions. Reducing the dimensionality introduces new phase transitions and serves as a testing ground for theoretical models. Especially one-dimensional systems show a very different behavior, due to the increased influence of quantum fluctuations.
We load a Bose-Einstein condensate (BEC) of cesium atoms into a 2D lattice formed by two retro-reflected lattice beams. The atoms are confined to a potential of an array of elongated tubes with tight transversal confinement. If the confinement is sufficiently deep and the atoms are sufficiently cold, any transversal motion will be “frozen out” and the atoms experience a quasi one-dimensional world.
In 1998, Maxim Olshanii predicted the existence of a new atomic scattering resonance in those one-dimensional systems . Since this resonance can be controlled and shaped by the confining potential, he called it a “confinement-induced resonance” (CIR). We observe this 1D resonance for the first time by means of a distinct atomic losses feature .
This work has been carried out in the CSIII experiment.
top, left to right
bottom, left to right:
 Beyond the Tonks-Girardeau Gas: Strongly Correlated Regime in Quasi-One-Dimensional Bose Gases
 Excitations of attractive 1D bosons: binding versus fermionization
 Atomic scattering in the presence of an external confinement and a gas of impenetrable bosons
Photos for download: ultracold media photos
German press release: Press release
more on confinement-induced resonances
The experiments are supported by the START-prize of the Bundesministerium für Wissenschaft und Forschung (BMWF) and the Austrian Science Fund (FWF) .
|last change: 09-09-20 by EH|