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Physical Review Letters

Raman Cooling of Cesium below 3 nK: New Approach Inspired by Lévy Flight Statistics

Jakob Reichel, F. Bardou, Maxime Dahan, E. Peik, Stephen Colby Rand, Ch Salomon, Claude N. Cohen-Tannoudji

Published Dec 18, 1995• 107 citations
Publisher

Abstract

We present a new approach to optimize subrecoil Raman cooling, based on L\'evy flight statistics. It shows that simple time sequences using square pulses can lead to very efficient cooling. We tested the method in a one-dimensional experiment with cesium atoms and obtained temperatures below 3 nK, less than $\frac{1}{70}$ of the single photon recoil temperature.

DOI
10.1103/physrevlett.75.4575

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We present a new approach to optimize subrecoil Raman cooling, based on L'evy flight statistics. It shows that simple time sequences using square pulses can lead to very efficient cooling. We tested the method in a one-dimensional experiment with cesium atoms and obtained temperatures below 3 nK, less than 170\frac{1}{70}701​ of the single photon recoil temperature.
We use velocity-selective Raman pulses generated by two diode lasers to cool cesium atoms in 1 dimension to an r.m.s. of 1.2 mm/s. This is about 1/3 of the single-photon recoil velocity v rec = ℏk/M , where ℏk is the photon momentum and M the atom's mass. The corresponding effective temperature is a factor of 9 below the single-photon recoil temperature given by k B T rec /2 = 1/2 Mv rec 2 . Because of the high cesium mass, this temperature is only (23 ± 5) nanokelvin, the lowest 1D kinetic temperature reported to date.
We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30nK30\phantom{\rule{0.3em}{0ex}}\mathrm{nK}30nK (0.15Trec)(0.15{T}_{\mathrm{rec}})(0.15Trec​). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.
We present a new and efficient implementation of Raman cooling of trapped atoms. It uses Raman pulses with an appropriate frequency chirp to realize a velocity selective excitation through a rapid adiabatic passage. This method allows to address in a single pulse a large number of non zero atomic velocity classes and it produces a nearly unity transfer efficiency. We demonstrate this cooling method using cesium atoms in a far-detuned crossed dipole trap. Three-dimensional cooling of 1×1051 \times 10^{5}1×105 atoms down to 2μ2 μ2μK is performed in 100 ms. In this preliminary experiment the final atomic density is 1.3×10121.3\times 10^{12}1.3×1012 at/cm3^33 (within a factor of 2) and the phase-space density increase over the uncooled sample is 20. Numerical simulations indicate that temperatures below the single photon recoil temperature should be achievable with this method.
We demonstrate a new cooling technique which is used to cool sodium atoms in one dimension to an effective temperature of 100 nK, less than 1/10 of the single photon recoil temperature kB{\mathit{k}}_{\mathit{B}}kB​Trec{\mathit{T}}_{\mathrm{rec}}Trec​=(\ensuremath{\Elzxh}k)2{)}^{2})2/2M.