Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Dark cold atoms at high densities

Wolfgang Ketterle, Kendall B. Davis, Michael Joffe, M.‐O. Mewes, David E. Pritchard

Published May 8, 1994• 0 citations
OpenAlex

Abstract

Optical trapping and cooling of atoms at high densities is limited by strong absorption of both the incident laser light and the emitted fluorescence. Reabsorption of the emitted fluorescence gives rise to repulsive forces between the trapped atoms and also to additional heating thus limiting both density and ultimate temperature. We have recently demonstrated a method to avoid these effects by shelving most of the atoms being trapped or cooled in a dark hyperfine state. At any instant, about one percent of the atoms are in the bright state where the trapping and cooling forces are exerted. This scheme ensures transparency of the atom cloud at very high optical densities.

Related papers

High densities of cold atoms in a dark spontaneous-force optical trap

Wolfgang Ketterle, Kendall B. Davis, Michael A. Joffe +2 more

A new magneto-optical trap is demonstrated which confines atoms predominantly in a ``dark'' hyperfine level, that does not interact with the trapping light. This leads to much higher atomic densities as repulsive forces between atoms due to rescattered radiation are reduced and trap loss due to excited-state collisions is diminished. In such a trap, more than ${10}^{10}$ sodium atoms have been confined to densities approaching ${10}^{12}$ atoms ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.

Physical Review Letters•Apr 12, 1993•528 citations

Laser cooling and trapping of atoms

G., T, C. G. Townsend

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 (< 10-10 Torr) background vapour pressure. The dependence of the cold collision loss coefficient β on the trapping intensity was measured to permit identification of the different cold collision processes. The largest loss rates observed were those due to hyperfine structure-changing collisions, with a coefficient β = (2±1) x 10-10cm3s-1. 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.

•Jan 1, 1995•0 citations

Laser cooling and trapping of atoms

G Townsend Christopher

 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.

•Jan 1, 1995•1 citation

Laser cooling and trapping of atoms

Christopher J. Foot

The development of laser cooling has an important impact on many aspects of atomic physics and quantum optics. The efforts to understand the various types of force exerted on atoms by laser light have led to some interesting physics and it is now possible for extremely cold clouds of atoms to be produced, which can be confined in atom traps or formed into very monoenergetic atomic beams. There are many new possibilities to explore in this ultra-cold regime where quantum effects are significant, in addition to the potential for great improvements in precision measurements made by r.f. and laser spectroscopy.

Contemporary Physics•Nov 1, 1991•41 citations

Dark spontaneous-force optical trap for sodium atoms

Wolfgang Ketterle, Kendall B. Davis, Michael Joffe +2 more

Since its invention the magneto-optical trap (MOT) has offered a relatively simple way to trap and study cold neutral atoms.1 However, the maximum density achieved in such a trap is much lower than is desirable for the study of cold collisions and the realization of evaporative cooling schemes. The density is limited by two processes; (1) trap loss due to excited-state collisions2 and (2) the repulsive force generated by the rescattering of photons.3

Quantum Electronics and Laser Science Conference•May 2, 1993•0 citations

Reabsorption of Light by Trapped Atoms

Yvan Castin, J. I. Cirac, Maciej Lewenstein

We investigate the effect of reabsorption of photons in laser cooling of trapped atoms, in view of a possible achievement of Bose-Einstein condensation by purely optical means. Reabsorption can be strongly suppressed by using strongly deformed traps and by reducing the fluorescence rate to a value smaller than the trap frequencies.

Physical Review Letters•Jun 15, 1998•88 citations
Optical trapping and cooling of atoms at high densities is limited by strong absorption of both the incident laser light and the emitted fluorescence. Reabsorption of the emitted fluorescence gives rise to repulsive forces between the trapped atoms and also to additional heating thus limiting both density and ultimate temperature. We have recently demonstrated a method to avoid these effects by shelving most of the atoms being trapped or cooled in a dark hyperfine state. At any instant, about one percent of the atoms are in the bright state where the trapping and cooling forces are exerted. This scheme ensures transparency of the atom cloud at very high optical densities.
A new magneto-optical trap is demonstrated which confines atoms predominantly in a ``dark'' hyperfine level, that does not interact with the trapping light. This leads to much higher atomic densities as repulsive forces between atoms due to rescattered radiation are reduced and trap loss due to excited-state collisions is diminished. In such a trap, more than 1010{10}^{10}1010 sodium atoms have been confined to densities approaching 1012{10}^{12}1012 atoms ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.
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 (< 10-10 Torr) background vapour pressure. The dependence of the cold collision loss coefficient β on the trapping intensity was measured to permit identification of the different cold collision processes. The largest loss rates observed were those due to hyperfine structure-changing collisions, with a coefficient β = (2±1) x 10-10cm3s-1. 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.
 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.
The development of laser cooling has an important impact on many aspects of atomic physics and quantum optics. The efforts to understand the various types of force exerted on atoms by laser light have led to some interesting physics and it is now possible for extremely cold clouds of atoms to be produced, which can be confined in atom traps or formed into very monoenergetic atomic beams. There are many new possibilities to explore in this ultra-cold regime where quantum effects are significant, in addition to the potential for great improvements in precision measurements made by r.f. and laser spectroscopy.