Two-stage magneto-optical trapping and narrow-line cooling ofLi6atoms to high phase-space density

Abstract

We report an experimental study of peak and phase-space density of a two-stage magneto-optical trap (MOT) of 6 Li atoms, which exploits the narrower 2S 1/2 → 3P 3/2 ultraviolet (UV) transition at 323 nm following trapping and cooling on the more common D2 transition at 671 nm. The UV MOT is loaded from a red MOT and is compressed to give a high phase-space density up to 3 × 10 −4 . Temperatures as low as 33 μK are achieved on the UV transition. We study the density limiting factors and in particular find a value for the light-assisted collisional loss coefficient of 1.3 ± 0.4 × 10 −10 cm 3 /s for low repumping intensity.

Cooling and thermometry of atomic Fermi gases

“…This strategy is especially suitable for forced evaporative cooling in optical traps, where many hyperfine states are trapped simultaneously, and it is progressively advantageous with increasing the hyperfine quantum number I, because the fraction of states available for s-wave elastic scattering with respect to the total available is 2I/(2I+1). For states with I = 1/2, this means only 50%, but in the case of I = 5/2 (for 173 Yb, for instance) this means that 5/6 of the possible combinations proceed with evaporative cooling unaffected by the Pauli principle. Limits to the minimum temperature achievable by means of dual evaporative cooling have been discussed, including Pauli blocking, leading to an estimate of (T /T F ) min 0.3 [61,62].…”

All-optical production and transport of a largeLi6quantum gas in a crossed optical dipole trap

“…As described in [21], the peak density reaches a transient maximum value during this stage, at which point the ramp-up is initiated. After a combined loading and cooling duration of 10 ms, the UV MOT is switched off by extinguishing the repumping light 0.5 ms in advance of the cooling light.…”

“…As the cloud thermalizes to the same temperature for all relevant detunings, the phase-space density follows the same curve. The UV frequency detuning of δ ≃ −3.2Γ 3P for maximum atom number differs from the detuning for the maximum phase-space density of the UV MOT, that was found to be δ ≃ −2.7Γ 3P [21]. The residual differential ac Stark shift of the cooling transition induced by the 1070 nm light cannot explain this difference, as it is small and increases the 2S 1/2 → 3P 3/2 transition frequency [1,23].…”

Narrow-linewidth cooling of $$^{6}$$ 6 Li atoms using the 2S-3P transition

“…This scheme has also been demonstrated in the alkali metal atoms for transitions from the ground state nS 1/2 to the excited state (n + 1)P 3/2 [25][26][27]. The linewidths of these transitions are much narrower than those of the D2 transitions, resulting in a much lower Doppler temperature.…”

“…For instance, the overall linewidth of the 2S 1/2 → 3P 3/2 transition of 6 Li at 323 nm is Γ 3P = 2π × 754 kHz, corresponding to a Doppler temperature of 18 µK that is much lower than the D2-line Doppler temperature of 141 µK. Temperatures as low as 59 µK and 33 µK have been experimentally achieved for 6 Li atoms in UV MOTs using this transition [25,26].…”