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Register a new user${Lambda}$-enhanced grey molasses on the $D_2$ transition of Rubidium-87 atoms
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Laser cooling based on dark states, i.e. states decoupled from light, has proven to be effective to increase the phase-space density of cold trapped atoms. Dark-states cooling requires open atomic transitions, in contrast to the ordinary laser cooling used for example in magneto-optical traps (MOTs), which operate on closed atomic transitions. For alkali atoms, dark-states cooling is therefore commonly operated on the $D_1$ transition $n S_{1/2}rightarrow n P_{1/2}$. We show that, for $^{87}text{Rb}$, thanks to the large hyperfine structure separations the use of this transition is not strictly necessary and that $$quasi-dark state$$ cooling is efficient also on the $D_2$ line, $5 S_{1/2}rightarrow 5 P_{3/2}$. We report temperatures as low as $(4.0pm 0.3),mu$K and an increase of almost an order of magnitude in the phase space density with respect to ordinary laser sub-Doppler cooling.
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Experiments on the spectroscopy of the Forster resonance Rb(37P)+Rb(37P) -> Rb(37S)+Rb(38S) and microwave transitions nP -> nS, nD between Rydberg states of cold Rb atoms in a magneto-optical trap have been performed. Under ordinary conditions, all spectra exhibited a 2-3 MHz line width independently of the interaction time of atoms with each other or with microwave radiation, although the ultimate resonance width should be defined by the inverse interaction time. Analysis of the experimental conditions has shown that the main source of the line broadening was the inhomogeneous electric field of cold photoions appeared at the excitation of initial Rydberg nP states by broadband pulsed laser radiation. Using an additional pulse of the electric field, which rapidly removed the photoions after the laser pulse, lead to a substantial narrowing of the microwave and Forster resonances. An analysis of various sources of the line broadening in cold Rydberg atoms has been conducted.
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 determine the frequency of the ultranarrow $^{87}text{Sr}$ ${^{1}text{S}_{0}} - {^{3}text{P}_{2}}$ transition by spectroscopy of an ultracold gas. This transition is referenced to four molecular iodine lines that are observed by Doppler-free saturation spectroscopy of hot iodine vapor. The frequency differences between the Sr and the I$_2$ transitions are measured with an uncertainty of 250 kHz. The absolute frequency of the $^{87}text{Sr}$ ${^{1}text{S}_{0}} - {^{3}text{P}_{2}}$ ($text{F}=7/2$) transition is 446648775(30) MHz and limited in accuracy by the iodine reference. This work prepares the use of the Sr ${^{1}text{S}_{0}} - {^{3}text{P}_{2}}$ transition for quantum simulation and computation.
We show that with a purely blue-detuned cooling mechanism we can densely load single neutral atoms into large arrays of shallow optical tweezers. With this ability, more efficient assembly of larger ordered arrays will be possible - hence expanding the number of particles available for bottom-up quantum simulation and computation with atoms. Using Lambda-enhanced grey molasses on the D1 line of 87Rb, we achieve loading into a single 0.63 mK trap with 89% probability, and we further extend this loading to 100 atoms at 80% probability. The loading behavior agrees with a model of consecutive light-assisted collisions in repulsive molecular states. With simple rearrangement that only moves rows and columns of a 2D array, we demonstrate one example of the power of enhanced loading in large arrays.
We report enhanced three-dimensional degenerated Raman sideband cooling (3D DRSC) of caesium (Cs) atoms in a standard single-cell vapour-loading magneto-optical trap. Our improved scheme involves using a separate repumping laser and optimized lattice detuning. We load $1.5 times 10^7$ atoms into the Raman lattice with a detuning of -15.5 GHz (to the ground F = 3 state). Enhanced 3D DRSC is used to cool them from 60 $mu$K to 1.7 $mu$K within 12 ms and the number of obtained atoms is about $1.2 times 10^7$. A theoretical model is proposed to simulate the measured number of trapped atoms. The result shows good agreement with the experimental data. The technique paves the way for loading a large number of ultracold Cs atoms into a crossed dipole trap and efficient evaporative cooling in a single-cell system.
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