Université Paris Nord / CNRS
Our experiment creates dipolar Bose Einstein Condensates (BECs) of Cr atoms. In the last decade, the study of such ultracold atom gases has become an interdisciplinary and fascinating field. The realization of degenerate quantum gases opens the way to perform fundamental studies in quantum physics with an almost ideal dilute system displaying tunable properties (density, temperature, interaction strength, ...). This model system can be studied in a highly versatile environment since confining potentials can be tailored at will. Furthermore, since the analysis protocols benefit from the reliability of the laser spectroscopy techniques, the comparison between experimental outcomes and theoretical predictions is much sounder than what is usually met in condensed matter.
To date the available atomic quantum gases are made of atoms interacting through isotropic short-range potentials. The long-range anisotropic dipole-dipole interaction between atoms carrying a large magnetic moment is expected to induce a wealth of new properties. For example, a supersolid phase arises when a dipolar quantum gas is transfered in a 2D lattice.
The magnetic dipole moment of chromium in the ground state is 6µB. Due to this exceptionally large dipole moment, chromium degenerate gases represent ideal systems to investigate quantum dynamics under the influence of dipolar interactions.
As a first stage to reach degeneracy, we set up a magneto-optical trap for the most abundant bosonic isotope 52Cr and for the fermionic isotope 53Cr. The two isotopes can be trapped separately as well as simultaneously producing a cold dipolar boson-fermion mixture. We studied the collisional properties of these cold gases. In a second stage, several millions 52Cr atoms are optically trapped at the focus of a powerful infrared laser at a temperature on the order of 100µK. Finally, we evaporatively cool the trapped 52Cr atoms down to degeneracy.
We have studied the collective excitations of the chromium BEC and demonstrated the impact of the anisotropic dipole-dipole interactions on the frequencies of the low-energy collective vibration modes of the trapped BEC. In a further set of experiments, we have studied S=3-spin dynamics using our Cr-BECs either in 3D or in restricted 2D and 1D geometries. At very low magnetic fields, spontaneous demagnetization occurs which enables the study of the S=3-spinor physics.
We plan to reach degeneracy for the fermionic isotope 53Cr , and to create strongly correlated systems, by extending our current experiments on the loading of our condensates into optical lattices. This will meet the current burst of interest in the statistical physics of such systems related to the field of quantum magnetism and will open new avenues for the processing of quantum information.
Selected recent publications
Q. Beaufils et al, All-optical Bose-Einstein Condensation of Chromium, Phys. Rev. A 77, 061601 R (2008);
G. Bismut et al., Collective excitations of a dipolar BEC, Phys. Rev. Lett., 105, 040404 (2010);
B. Pasquiou et al., Spin relaxation and band excitation of a dipolar BEC in 2D optical lattices, Phys. Rev. Lett. 160, 015301 (2011)
Olivier GORCEIX, Pr. (group leader),
Bruno LABURTHE-TOLRA, CNRS Research Associate,
Etienne MARECHAL, CNRS Engineer,
Paolo PEDRI, Assistant Professor,
Laurent VERNAC, Assistant Professor,
Gabriel BISMUT, PhD student,
Benjamin PASQUIOU, PhD student,
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