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Conference on Lasers and Electro-Optics

Preparation of single velocity atoms for matter wave interferometry

T. Binnewies, Uwe Sterr, J. Helmcke, F. Riehle

Published Aug 29, 2005• 0 citations

Abstract

Summary form only given. Atoms without ground state splitting, e.g. alkaline earths, are of special interest for atom interferometry and frequency standards due to their small sensitivity to external fields and for BEC and the study of cold collisions due to the simplified theoretical interpretation of their interaction. We demonstrate Maxwell's-demon cooling, a novel method which allows to further cool alkaline earth atoms in one dimension. It consists of three consecutive steps which are repeated several times. First, from a cloud of cooled atoms released from a standard magneto-optical trap a small part of the velocity distribution is selected by excitation on a narrow transition (intercombination transition). Second, these atoms are optically pumped to another long lived state. Third, the ground state velocity distribution is restored by turning on the optical molasses on the strong transition used for the magneto-optical trapping. In addition to Maxwell's thought experiment, where a demon separates the cold atoms from the hot ones, in the novel scheme the hot atoms are furthermore cooled again to the original 3 mK. By repeating these steps slow atoms are accumulated in the excited state. The velocity distribution of the atoms is measured after the cold atoms are decayed to the ground state by recording the Doppler broadening of the intercombination transition.

DOI: 10.1109/iqec.2000.907926

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ABSTRACT In a ceramic vapor cell we have created a robust Sr magneto-optical trap that stores about 108 atoms with lifetimes>200 ms. We eliminate the 5p 1P14d 1D2*5p 3P2 leak and achieve a 10-fold improvement in trap lifetime byrepumping the 5p 3Po,2 dark states with 679 nm and 707 nm light. The observed lifetime is now limited by coldcollision losses, and we have preliminary measurements of the 2-body loss rate. Direct readout of the trap velocity distribution is possible using the narrow (7 kHz) 52 'S0----5p 3P1 intercombination line at 689 nm. We can also cool with this narrow transition and have achieved a 40-fold 1-D velocity compression for about 5% of the trapped atoms by applying this second-stage cooling. Keywords: Laser cooling, laser trapping, alkaline earths, cold collisions, frequency metrology 1. INTRODUCTION Laser cooling and trapping techniques have advanced to become an important tool of the atomic physics community, and in recent years there has been considerable interest in expanding the range of trapped elements. The alkalineearths, in particular, possess unique characteristics which make them interesting to trap. Studies of long-rangeatom-atom interactions are simplified because they have no hyperfine structure, and their narrow intercombinationtransitions make them excellent candidates for optical frequency standards. Furthermore, Doppler cooling with thesenarrow transitions can reduce temperatures to near the recoil limit.The most abundant alkaline earth isotopes have I =

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We describe a setup for a deep optical dipole trap or lattice designed for holding atoms at temperatures of a few mK, such as alkaline-Earth atoms which have undergone only regular Doppler cooling. We use an external optical cavity to amplify 3.2 W from a commercial single-frequency laser at 532 nm to 523 W. Powers of a few kW, attainable with low-loss optics or higher input powers, allow larger trap volumes for improved atom transfer from magneto-optical traps. We analyze possibilities for cooling inside the deep trap, the induced Stark shifts for calcium, and a cancellation scheme for the intercombination clock transition using an auxiliary laser.

We present an elegant application of matter-wave interferometry to the velocimetry of cold atoms whereby, in analogy to Fourier transform spectroscopy, the one-dimensional velocity distribution is manifest in the frequency domain of the interferometer output. By using stimulated Raman transitions between hyperfine ground states to perform a three-pulse interferometer sequence, we have measured the velocity distributions of clouds of freely expanding

^{85}\mathrm{Rb}

atoms with temperatures of 34 and $18\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{K}$. Quadrature measurement of the interferometer output as a function of the temporal asymmetry yields velocity distributions with excellent fidelity. Our technique, which is particularly suited to ultracold samples, compares favorably with conventional Doppler and time-of-flight techniques, and it reveals artefacts in standard Raman Doppler methods. The technique is related to, and provides a conceptual foundation of, interferometric matter-wave accelerometry, gravimetry, and rotation sensing.

We consider laser cooling and trapping of alkaline-earth and similar atoms in a bichromatic field resonant to a closed optical transition 1S0→1P1 or 1S0→3P1. It is shown that new kinetic effects emerge compared to monochromatic fields, enabling the formation of a deep macroscopic trap capable of capturing and cooling neutral atoms to sub-Doppler temperatures. Such a purely optical macroscopic trap can serve as an alternative to the well-known magneto-optical trap and can be used in applications requiring minimization of the magnetic field in the cold atom cloud region. The obtained results are of interest for the new generation of quantum sensors and optical frequency standards.