Thermodynamical approaches to efficient sympathetic cooling in ultracold Fermi-Bose atomic mixtures

Abstract

We discuss the cooling efficiency of ultracold Fermi-Bose mixtures in species-selective traps using a thermodynamical approach. The dynamics of evaporative cooling trajectories is analyzed in the specific case of bichromatic optical dipole traps also taking into account the effect of partial spatial overlap between the Fermi gas and the thermal component of the Bose gas. We show that large trapping frequency ratios between the Fermi and the Bose species allow for the achievement of a deeper Fermi degeneracy, consolidating in a thermodynamic setting earlier arguments based on more restrictive assumptions. In particular, we confirm that the minimum temperature of the mixture is obtained at the crossover between boson and fermion heat capacities, and that below such a temperature sympathetic cooling vanishes. When the effect of partial overlap is taken into account, optimal sympathetic cooing of the Fermi species may be achieved by properly tuning the relative trapping strength of the two species in a time-dependent fashion. Alternatively, the dimensionality of the trap in the final stage of cooling can be changed by increasing the confinement strength, which also results in a crossover of the heat capacities at deeper Fermi degeneracies. This technique may be extended to Fermi-Bose degenerate mixtures in optical lattices.

13 pages, 9 figures, higher quality figures in published version

References in corpus (14)

• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas
• Quantum degenerate two-species Fermi-Fermi mixture coexisting with a Bose-Einstein condensate
• Species-specific optical lattices
• Mixtures of Bosonic and Fermionic Atoms in Optical Lattices
• Critical velocity for superfluid flow across the BEC-BCS crossover
• Measurement of the Entropy and Critical Temperature of a Strongly Interacting Fermi Gas
• Observation of deviations from ideal gas thermodynamics in a trapped Bose-Einstein condensed gas
• Feshbach resonances in mixtures of ultracold ${}^6$Li and ${}^{87}$Rb gases
• High-Temperature Atomic Superfluidity in Lattice Boson-Fermion Mixtures
• Engineering Superfluidity in Bose-Fermi Mixtures of Ultracold Atoms
• Ultracold Thermalization of ${}^7$Li and ${}^{87}$Rb
• Formation of Ultracold Heteronuclear Dimers in Electric Fields
• Development of an apparatus for cooling 6Li-87Rb Fermi-Bose mixtures in a light-assisted magnetic trap