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Register a new userComparison of an efficient implementation of gray molasses to narrow-line cooling for the all-optical production of a lithium quantum gas
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We present an efficient scheme to implement a gray optical molasses for sub-Doppler cooling of $^{6}$Li atoms with minimum experimental overhead. To integrate the $D_1$ light for the gray molasses (GM) cooling into the same optical setup that is used for the $D_2$ light for a standard magneto-optical trap (MOT), we rapidly switch the injection seeding of a slave laser between the $D_2$ and $D_1$ light sources. Switching times as short as $30,mutextrm{s}$ can be achieved, inferred from monitor optical beat signals. The resulting low-intensity molasses cools a sample of $N=9times10^8$ atoms to about $60,mutextrm{K}$. A maximum phase-space density of $rho=1.2times10^{-5}$ is observed. On the same setup, the performance of the GM is compared to that of narrow-line cooling in a UV MOT, following the procedure in Sebastian et al. (2014). Further, we compare the production of a degenerate Fermi gas using both methods. Loading an optical dipole trap from the gray molasses yields a quantum degenerate sample with $3.3times10^5$ atoms, while loading from the denser UV MOT yields $2.4times10^6$ atoms. Where the highest atom numbers are not a priority this implementation of the gray molasses technique yields sufficiently large samples at a comparatively low technical effort.
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Robust cooling and nondestructive imaging are prerequisites for many emerging applications of neutral atoms trapped in optical tweezers, such as their use in quantum information science and analog quantum simulation. The tasks of cooling and imaging can be challenged, however, by the presence of large trap-induced shifts of their respective optical transitions. Here, we explore a system of $^{39}$K atoms trapped in a near-detuned ($780$ nm) optical tweezer, which leads to relatively minor differential (ground vs. excited state) Stark shifts. We demonstrate that simple and robust loading, cooling, and imaging can be achieved through a combined addressing of the D$_textrm{1}$ and D$_textrm{2}$ transitions. While imaging on the D$_textrm{2}$ transition, we can simultaneously apply $Lambda$-enhanced gray molasses (GM) on the D$_textrm{1}$ transition, preserving low backgrounds for single-atom imaging through spectral filtering. Using D$_textrm{1}$ cooling during and after trap loading, we demonstrate enhanced loading efficiencies as well as cooling to low temperatures. These results suggest a simple and robust path for loading and cooling large arrays of potassium atoms in optical tweezers through the use of resource-efficient near-detuned optical tweezers and GM cooling.
Gray molasses is a powerful tool for sub-Doppler laser cooling of atoms to low temperatures. For alkaline atoms, this technique is commonly implemented with cooling lasers which are blue-detuned from either the D1 or D2 line. Here we show that efficient gray molasses can be implemented on the D2 line of 40K with red-detuned lasers. We obtained temperatures of 48(2) microKelvin, which enables direct loading of 9.2(3)*10^6 atoms from a magneto-optical trap into an optical dipole trap. We support our findings by a one-dimensional model and three-dimensional numerical simulations of the optical Bloch equations which qualitatively reproduce the experimentally observed cooling effects.
We report on the realization of sub-Doppler laser cooling of sodium atoms in gray molasses using the D1 optical transition ($3s, ^2S_{1/2} rightarrow 3p, ^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing $3times10^9$ atoms, previously cooled to 350 $mu$K in a magneto-optical trap, and it leads to temperatures as low as 9 $mu$K and phase-space densities in the range of $10^{-4}$. The capture efficiency of the gray molasses is larger than 2/3, and we observe no density-dependent heating for densities up to $10^{11}$ cm$^{-3}$.
Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin-polarized with temperatures reaching below 2 microkelvin. Our results constitute an alternative method for laser cooling on weak transitions, applicable to rare-earth-metal and metastable alkaline earth elements.
We systematically investigate the dependence of the temperature of cold cesium atoms of polarization gradient cooling (PGC) in optical molasses on experimental parameters, which contain changing modes of cooling laser, PGC interaction time, cooling laser frequency and its intensity. The SR mode of cooling laser, that means the cooling laser frequency is changed with step mode and cooling laser intensity is changed with ramp mode, is found to be the best for PGC comparing with other SS, RS, and RR modes. We introduce a statistical explanation and an exponential decay function to explain the variation of cold atomic temperature on time. The heating effect is observed when the cooling laser intensity is lower than the saturation intensity of cold atoms. After optimization, the lowest temperature of cold cesium atoms is observed to be about 4uK with the number of 2x10^9, a density of 1x10^11/cm^3 and the phase space density of 4.4x10^(-5). The optimization process and analysis of controllable experimental parameters are also meaningful for other cold atomic systems.
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