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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Degenerated atomic gas in a dark magneto-optical lattice

А. В. Тайченачев, Anatolii M Tumaikin, Valeriy I. Yudin

Published Oct 21, 1998• 0 citations
Publisher

Abstract

It is shown that in the dark magneto-optical lattices the effects connected with the Bose-statistics of particles can be observed under the laser cooling temperature (10-4 - 10-6 K), that is orders of magnitude higher than the evaporative cooling temperature in magnetic traps. There appears the quasicondensation, when the wave function is formed at the localization distance of atoms in a single well. Apart from this, we show that the adiabatic reducing of the magnetic field leads to the increasing of the temperature and the Bose-condensation in the whole lattice can take place. The field configuration, where the form of the three-dimensional magneto-optical potential does not depend on phases of light waves, is found.

DOI
10.1117/12.328292

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•Jan 1, 1995•1 citation
It is shown that in the dark magneto-optical lattices the effects connected with the Bose-statistics of particles can be observed under the laser cooling temperature (10-4 - 10-6 K), that is orders of magnitude higher than the evaporative cooling temperature in magnetic traps. There appears the quasicondensation, when the wave function is formed at the localization distance of atoms in a single well. Apart from this, we show that the adiabatic reducing of the magnetic field leads to the increasing of the temperature and the Bose-condensation in the whole lattice can take place. The field configuration, where the form of the three-dimensional magneto-optical potential does not depend on phases of light waves, is found.
We show that in dark magneto-optical lattices, effects associated with the Bose statistics of atoms can be observed even at laser cooling temperatures (10 −4 –10 −6 K), which exceed evaporative cooling temperatures in magnetic traps by several orders of magnitude. Quasicondensation occurs, i.e., the wave function is formed over the distances on which atoms are localized near the bottom of a separate potential well. In addition, switching off the magnetic field adiabatically reduces the temperature significantly, as a result of which Bose condensation in the entire volume of the gas can be observed. We propose a configuration of the light and magnetic fields in which the shape of the three-dimensional magneto-optical potential is independent of the phases of the emerging light waves.
The motion of atoms in a dark magneto-optical lattice is considered. This lattice is formed by a non-uniformly polarized laser field in the presence of a static magnetic field. Cold atoms are localized in the vicinity of points where dark states are not destroyed by a magnetic field. As a result, the optical interaction tends to zero (dark or grey lattices). Depending on the field configuration such a lattice can exhibit one-dimensional (1D) or two-dimensional (2D) periodicity. It is shown that in 1D and 2D dark magneto-optical lattices the effects connected with the Bose statistics of particles can be observed under temperatures 10 -5 -10 -6 K and densities 10 11 -10 12 cm -3 , i.e. those that are usual for current experiments on laser cooling.
The motion of atoms in a dark magneto-optical lattice is considered. This lattice is formed by a nonuniformly polarized laser field in the presence of a static magnetic field. Cold atoms are localized in the vicinity of points where dark states are not destroyed by a magnetic field. As a result, the optical interaction tends to zero (dark or gray lattices). Depending on the field configuration, such a lattice can exhibit one, two, or three-dimensional periodicity. It is shown that in 1D and 2D, mark magneto- optical lattices the effects connected with the Bose- statistics of particles can be observed under the temperature 10-5 - 10-6K and densities 1011 - 1012cm-3, those are usual for current experiments on laser cooling.
The dark magneto-optical lattice for atoms with J yields J -1 transition is considered. The periodic potential is formed using a (sigma) + - (sigma) - laser field and a uniform magnetic field orthogonal to the light waves propagation. The dynamics of slowly moving atoms is investigated for J equals 1 in the quasiclassical approximation. The cases of a weak and strong dark states destruction by the magnetic field are analyzed. The sub- Doppler cooling for a blue detuning from resonance is demonstrated for a low laser field power. The dark atomic lattice creation in the case of the light-induced shift is much less than the Zeeman splitting is predicted.
We investigate the coherence properties of an atomic beam evaporatively cooled in a magnetic guide, assuming thermal equilibrium in the quantum degenerate regime. The gas experiences two-dimensional, transverse Bose-Einstein condensation rather than a full three-dimensional condensation because of the very elongated geometry of the magnetic guide. First order and second order correlation functions of the atomic field are used to characterize the coherence properties of the gas along the axis of the guide. The coherence length of the gas is found to be much larger than the thermal de Broglie wavelength in the strongly quantum degenerate regime. Large intensity fluctuations present in the ideal Bose gas model are found to be strongly reduced by repulsive atomic interactions; this conclusion is obtained with a one-dimensional classical field approximation valid when the temperature of the gas is much higher than its chemical potential, kBT ≫ |µ|. Pacs: 03.75.Fi, 42.50.-p The first experimental achievements of Bose-Einstein condensates in atomic vapors [1, 2, 3, 4] have opened promising perspectives for atom optics: condensates constitute indeed atomic waves sources of much better coherence properties than the usual ‘thermal ’ sources like the standard magneto-optical trap. These
 A detailed experimental and theoretical investigation of a magneto-optical trap for caesium atoms is presented. Particular emphasis has been placed on achieving high spatial number densities and low temperatures. Optimizing both of these together enables efficient evaporative cooling from a conservative trap, a procedure which has recently led to the first observations of Bose-Einstein condensation in a dilute atomic vapour. The behaviour of a magneto-optical trap is nominally determined by four independent parameters: the detuning and intensity of the light field, the magnetic field gradient and the number of trapped atoms. A model is presented which incorporates previous treatments into a single description of the trap that encompasses a wide range of its behaviour. This model was tested quantitatively by measuring the temperature of the cloud and its spatial distribution as a function of the four parameters. The maximum density was found to be limited both by the reabsorption of photons scattered within the cloud and by a reduction of the confining force at small light shifts. The nonlinear variation with position of the restoring force was found to be significant in limiting the number of atoms confined to a high density. A maximum density in phase space (defined as the number of atoms in a box with sides of dimension one thermal de Broglie wavelength) of (1.5 ± 0.5) x 10-5 was observed, with a spatial density of 1.5 x 1011 atoms per cm3. Cold collision losses from a caesium magneto-optical trap have been studied with the purpose of assessing their influence on spatial densities. In contrast to previous measurements of similar quantities, these measurements did not require the use of an ultra-low ( A study is presented of a modified magneto-optical trap in which a fraction of the population is shelved into a hyperfine level that does not interact with the trapping light. In this so-called dark magneto-optical trap, improved densities of nearly 1012cm-3 have been previously reported for sodium. The application of the technique to caesium is not straightforward due to the larger excited state hyperfine splittings. A simple theory for caesium is presented and its main predictions verified by measurements of density, number and temperature. A density of nearly 1012cm,-3 was indeed obtained but at a temperature substantially higher than in the conventional magneto-optical trap.