No abstract

Stimulated Raman transitions between the ground-level hyperfine states of atoms have been used to manipulate slowly moving atoms in an atomic fountain. An ensemble of sodium atoms with an inferred velocity spread along one dimension of 270 jum/sec has been prepared by this technique. We also show that this velocity-selection method is effective in measuring ultracold temperatures of laser-cooled atoms in a regime where traditional ballistic methods fail.PACS numbers: 32.80.PjThere has been dramatic progress in the cooling and manipulation of atoms in recent years. For example, atoms in optical molasses 1 with polarization gradients 2 have been cooled to temperatures well below the Doppler limit kBT = hr/2. 3 Temperatures as low aswhere hk is the momentum recoil due to the photon used in the cooling process, have been observed for sodium 3 ' 4 ( -30 /iK) and cesium ( -2.5 pK). 5 Helium atoms have been "cooled" in one dimension to 2 pK, a factor of 2 below the recoil limit (hk) 2 /2M, by velocity-selective coherent population trapping. 6 In this paper, we describe a new type of optical velocity selection that has been shown to prepare a sample of atoms with a velocity spread 2 orders of magnitude below the velocity an atom would experience from the recoil of a single photon. This velocity spread can be characterized by an effective one-dimensional "temperature" of 24 pK. We further show that this technique will be useful in measuring the velocity spreads of atoms for AD< 1 cm/sec, where time-of-flight techniques 1,2 are no longer effective because of gravitational acceleration. Other applications of this velocity-selection method will also be indicated in this paper.The velocity-selected atoms are prepared as follows: Atoms with a ground-state hyperfine splitting v\2 and an optical interval vn as shown in Fig. 1 are first optically pumped into a single hyperfine level |l>. Two counterpropagating laser beams at frequencies V\L and VIL will induce a stimulated Raman transition to the |2) state if atoms are in resonance with the frequency difference vi2 as vi/, -V2L-7 The atoms excited into the |2) state will have a velocity spread given by the Doppler-shift formula Av/c SB AV/(V\L + V2L\ where Av is the linewidth of the transition. The velocity spread Av can be extremely narrow because the frequencies VIL,2L are optical frequencies and the linewidth of the 11>-• |2> transition can be narrow. If the laser frequency V2L = VIL +Vrf is generated by an electro-optic modulator or other radiofrequency technique, the frequency jitter of the laser is canceled out. The linewidth due to the finite transit time is greatly reduced with the use of slow atoms. For example, we have demonstrated a 2-Hz-wide resonance of the sodium ground-state hyperfine splitting with atoms in an atomic fountain. 8 Even with a modest measurement time of 10 msec, the expected spread in velocity Av is 30 ^m/sec for sodium atoms.The basic experimental apparatus has been previously described. 8 Atoms from a thermal beam were slowed with a counterpropagat...

No abstract

. (2013) A surface-patterned chip as a strong source of ultracold atoms for quantum technologies. Nature Nanotechnology, 8 (5). pp. 321-324. Copyright © 2013 MacMillanA copy can be downloaded for personal non-commercial research or study, without prior permission or chargeThe content must not be changed in any way or reproduced in any format or medium without the formal permission of the copyright holder(s) Laser cooled atoms are central to modern precision measurements 1-6 . They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics 7,8 , quantum information processing 9-11 and matter wave interferometry 12 . Although significant progress has been made in miniaturising atomic metrological devices 13,14 , these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefit from the advantages of atoms in the microKelvin regime 15,16 . However, simplifying atomic cooling and loading using microfabrication technology has proved difficult 17,18 . In this letter we address this problem, realising an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, at sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with the simplicity of fabrication and the ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices.

Laser-cooled sodium atoms pushed up on a vertical trajectory by radiation pressure are observed to turn around due to gravity. The relatively long time the atoms spent freely falling in this "atomic foun-tain^ allowed the ground-state hyperfine splitting to be measured with a linewidth of 2 Hz. After a 1000-sec integration time, the center of the line was resolved to ± 10 mHz. The absolute splitting was measured to be 1 771 626 129(2) Hz.