Atom-number probing for deep degeneracy determination of 6Li atoms in an optical dipole trap

Abstract

We produce a deeply degenerate Fermi gas of ⁶Li atoms via evaporative cooling in an optical dipole trap (ODT). The deep degeneracy is determined by observing total population saturation at the theoretical boundary, verified with finite-temperature fitting and in situ absorption imaging. The Pauli blocking at $T\approx 0.3T_F$ is circumvented through atom spilling by continuously reducing the ODT depth below $1.2E_F$, leading to the gas temperature below $0.1T_F$. The many-body mean field parameter $\beta =-0.63$ at zero temperature, extrapolated from in-trap Thomas–Fermi cloud sizes, yields a corrected temperature, $T/T_F<0.1$. Finally, a magnetic field sweep across the Feshbach resonance point (834 G) converts the cold Fermi gas into a molecular Bose–Einstein condensate of paired ⁶Li atoms, providing conclusive evidence of deep quantum degeneracy.