Chromium dipolar Fermi sea

Abstract

We report on the production of a degenerate Fermi gas of 53 Cr atoms, polarized in the state F=9/2, mF = −9/2, by sympathetic cooling with bosonic S=3, mS = −3 52 Cr atoms. We load in an optical dipole trap 3 ×10 4 53 Cr atoms with 10 6 52 Cr atoms. Despite this initial small number of fermionic atoms, we reach a final temperature of T ≃ 0.6 × T f (Fermi temperature), with up to 10 3 53 Cr atoms. This surprisingly efficient evaporation stems from an inter-isotope scattering length |aBF | = 85(±10) aB (Bohr radius) which is small enough to reduce evaporative losses of the fermionic isotope, but large enough to insure thermalization.PACS numbers: 03.75. Ss , 37.10.De, 67.85.Pq There has recently been tremendous activity on dipolar quantum gases. This is due to the fact that in dipolar gases the particles interact through long-range and anisotropic dipole-dipole interactions (DDIs), which drastically changes the nature of many-body ground and excited states. [15,16], due to anisotropic short range interactions. As this density promises to be even higher in the context of spinor gases where more than one spin state is populated, study of magnetism might be difficult with these atoms. For this reason, chromium, with a combination of relatively strong dipole-dipole long-range anisotropic interactions and simple isotropic short range interactions, remains a unique atom for the study of the unconventional spinor properties of dipolar quantum degenerate Fermi gases.Despite its interest, producing a dipolar Fermi gas of chromium atoms has been elusive for many years, as it represents a real experimental challenge. The main reason is the small number of 53 Cr atoms that can be captured in a magneto-optical trap (MOT), at most typically 10 5 , due to relatively small natural abundance, the complex hyperfine structure, and, most importantly, the very large light-assisted loss rate in a MOT [17]. In this paper, we describe and demonstrate a way to produce quantum gases of fermionic 53 Cr atoms.Our scheme consists in loading a mixture of mostabundant 52 Cr atoms and minority 53 Cr atoms in the same far-detuned optical dipole trap (ODT), and in performing forced evaporative cooling. Evaporative losses are smaller for 53 Cr atoms than for 52 Cr atoms, which results in very efficient evaporative cooling characterized by a gain of typically four orders of magnitude in phasespace density for one order of magnitude of atom losses. As a consequence, although only 3 × 10 4 53 Cr atoms are loaded in the dipole trap at 60 µK before evaporation, degenerate Fermi gases of up to 10 3 atoms can be produced in less than 15 s. We analyze our evaporation scheme and are able to point out the decisive role played by the numerical value of the inter-isotope scattering length, which is smaller than the bosonic scattering length. We measure this quantity, and compare it with theoretical predictions based on mass scaling [18].Fermi statistics leads to vanishing s-wave collisions due to Van der Walls interactions at low temperatures for polarize...

Entanglement and fluctuations in the XXZ model with power-law interactions

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Interaction-driven Lifshitz transition with dipolar fermions in optical lattices

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