UMR 5672

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Spin dynamics and thermodynamics with quantum dipolar gases

Laurent Vernac (Laboratoire de Physique des Lasers, Paris XIII)
When May 04, 2015
from 11:00 to 12:30
Where Centre Blaise Pascal
Attendees Laurent Vernac
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I will present experimental results obtained in our group with quantum gases made of chromium atoms. Due to the high spin (S=3) in the ground state of chromium, there are large magnetic dipole-dipole interactions (DDIs) between the atoms, which are long range, and anisotropic. They confer specific properties to chromium BECs, such as an anisotropic speed of sound. The main part of my talk will be devoted to our study of spin exchange dynamics in a 3D optical lattice. In the Mott insulator state, with one or two atoms per lattice site, DDIs trigger spin dynamics between atoms occupying different sites. Our system is well described by an effective XXZ spin Hamiltonian with true spin-spin interactions, providing thus an interesting platform for quantum simulation. As correlations build up between the few thousands of atoms loaded in the lattice, our system should reveal the existence of entanglement between many particles, through the finding of a relevant experimental entanglement witness. New perspectives are offered by our recent production of a chromium quantum gas with the fermionic isotope (Fermi Sea). I will as well describe our recent results demonstrating a new cooling mechanism based on spin filtering. The main assumption is that the BEC remains polarized in the lowest energy spin state. In that case, when the magnetic field is reduced, DDIs populate excited spin states in the thermal phase. Therefore, removing spin excited atoms leads to an increase of the BEC fraction, and consequently the entropy of the sample decreases. I will discuss perspectives to apply this scheme to non-dipolar species to reach temperatures below 1 nK.

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