Ultracold Chromium: a dipolar quantum gas

S. Hensler, J. Werner, Axel Griesmaier +5 more

Juergen Stuhler, Joerg Werner, Axel Griesmaier +4 more

Thierry Lahaye, Tobias Benedikt Koch, M. Fattori +2 more

Benjamin Lev

Axel Griesmaier, J. Stühler, Tilman Pfau

We have observed Bose-Einstein condensation of chromium atoms [1], whose large magnetic dipole moment is unique among all species that have been Bose-condensed so far. The arising magnetic forces are of anisotropic and long-range character and therefore introduce a novel type of interaction in the physics of ultracold quantum gases. In addition, it is expected that the character of the interaction present in a chromium BEC can be varied from mainly contact to purely dipolar utilizing one of the recently observed Feshbach resonances in 52Cr-collisions.

Thierry Lahaye, Tobias Benedikt Koch, M. Fattori +3 more

Due to its large magnetic moment of 6 muB, atomic chromium is the only Bose-Einstein condensed species so far to show relatively large magnetic dipole-dipole interactions (MDDI) besides the usual s-wave contact interaction. The long-range (1/r3) and anisotropic character of the MDDI gives birth to unique properties for the Cr Bose-Einstein condensate obtained recently in our group. In particular, it leads to an anisotropic deformation of the expanding condensate which depends on the orientation of the atomic dipole moments (Giovanazzi et al., 2006). In these measurements the dominant interaction is the contact one. We used expansion dynamics measurements to quantify the ratio between dipolar and contact interactions to be epsivdd= 0.159 plusmn 0.034 . This in turn provides a new experimental determination of the chromium scattering length: a = (96 plusmn 20) a0with an accuracy which is not limited by errors in the measurement of the atom number.