We report on experiments exploring the physics of dipolar quantum gases using a 52 Cr Bose-Einstein condensate (BEC). By means of a Feshbach resonance, it is possible to reduce the effects of short range interactions and reach a regime where the physics is governed by the long-range, anisotropic dipole-dipole interaction between the large (6 µB) magnetic moments of Chromium atoms. Several dramatic effects of the dipolar interaction are observed: the usual inversion of ellipticity of the condensate during time-of flight is inhibited, the stability of the dipolar gas depends strongly on the trap geometry, and the explosion following the collapse of an unstable dipolar condensate displays d-wave like features.We report on experiments exploring the physics of dipolar quantum gases using a 52 Cr Bose-Einstein condensate (BEC). By means of a Feshbach resonance, it is possible to reduce the effects of short range interactions and reach a regime where the physics is governed by the long-range, anisotropic dipole-dipole interaction between the large (6 µB) magnetic moments of Chromium atoms. Several dramatic effects of the dipolar interaction are observed: the usual inversion of ellipticity of the condensate during time-of flight is inhibited, the stability of the dipolar gas depends strongly on the trap geometry, and the explosion following the collapse of an unstable dipolar condensate displays d-wave like features.

Aug 4, 20136 citations

Dipolar Bose gas in a highly anharmonic trap

Francesco Ancilotto, Flavio Toigo

By means of mean-field theory, we have studied the structure and excitation spectrum of a purely dipolar Bose gas in a pancake shaped trap where the confinement in the $x$ - $y$ plane is provided by a highly anharmonic potential, resulting in an almost uniform confinement in the plane. We show that the stable condensates are characterized by marked radially structured density profiles. The stability diagram is calculated by independently varying the strength of the interaction and the trap geometry. By computing the Bogoliubov excitation spectrum near the instability line we show that soft ``angular'' rotons are responsible for the collapse of the system. The free expansion of the cloud after the trap is released is also studied by means of time-dependent calculations, showing that a prolate cigar-shaped condensate is dynamically stabilized during the expansion, which would otherwise collapse. Dipolar condensates rotating with sufficiently high angular velocity show the formation of multiply quantized giant vortices, while the condensates acquire a ring-shaped form.By means of mean-field theory, we have studied the structure and excitation spectrum of a purely dipolar Bose gas in a pancake shaped trap where the confinement in the $x$-$y$ plane is provided by a highly anharmonic potential, resulting in an almost uniform confinement in the plane. We show that the stable condensates are characterized by marked radially structured density profiles. The stability diagram is calculated by independently varying the strength of the interaction and the trap geometry. By computing the Bogoliubov excitation spectrum near the instability line we show that soft ``angular'' rotons are responsible for the collapse of the system. The free expansion of the cloud after the trap is released is also studied by means of time-dependent calculations, showing that a prolate cigar-shaped condensate is dynamically stabilized during the expansion, which would otherwise collapse. Dipolar condensates rotating with sufficiently high angular velocity show the formation of multiply quantized giant vortices, while the condensates acquire a ring-shaped form.

arXiv:1401.2261Physical Review AFeb 14, 20147 citations

Strongly Dipolar Quantum Gas of Molecules

Siwei Zhang

Oct 6, 20260 citations

Stability and collapse dynamics of dipolar Bose-Einstein condensates in one-dimensional optical lattices

Stefan Müller

The subject of this thesis is the experimental investigation of a dipolar 52-Chromium Bose-Einstein condensate (BEC) in a one-dimensional optical lattice potential. At first, the influence of the periodic landscape on the stability of the quantum gas is investigated. Based on these measurements, the collapse dynamics of the system, i.e. its time evolution after passing the threshold to the unstable regime, is observed and analyzed. Both the investigations aim to contribute to the basic understanding of dipolar quantum gases. In addition, they may provide a basis for further experiments with dipolar BECs in optical lattices. Amongst others, the observation of self-organized density structures is one of the biggest goals in this field of research.The subject of this thesis is the experimental investigation of a dipolar 52-Chromium Bose-Einstein condensate (BEC) in a one-dimensional optical lattice potential. At first, the influence of the periodic landscape on the stability of the quantum gas is investigated. Based on these measurements, the collapse dynamics of the system, i.e. its time evolution after passing the threshold to the unstable regime, is observed and analyzed. Both the investigations aim to contribute to the basic understanding of dipolar quantum gases. In addition, they may provide a basis for further experiments with dipolar BECs in optical lattices. Amongst others, the observation of self-organized density structures is one of the biggest goals in this field of research.

Jan 1, 20131 citation

By means of mean-field theory, we have studied the structure and excitation spectrum of a purely dipolar Bose gas in a pancake shaped trap where the confinement in the

x

y

plane is provided by a highly anharmonic potential, resulting in an almost uniform confinement in the plane. We show that the stable condensates are characterized by marked radially structured density profiles. The stability diagram is calculated by independently varying the strength of the interaction and the trap geometry. By computing the Bogoliubov excitation spectrum near the instability line we show that soft ``angular'' rotons are responsible for the collapse of the system. The free expansion of the cloud after the trap is released is also studied by means of time-dependent calculations, showing that a prolate cigar-shaped condensate is dynamically stabilized during the expansion, which would otherwise collapse. Dipolar condensates rotating with sufficiently high angular velocity show the formation of multiply quantized giant vortices, while the condensates acquire a ring-shaped form.