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

A study of collisional trap loss in ultra-cold trapped lithium-6 and lithium-7

Nicholas W. M. Ritchie

Published Jan 1, 1994• 0 citations
OpenAlex

Abstract

Measurements of the trap loss rate in ultra-cold magneto-optically trapped $\\sp6$Li and $\\sp7$Li are presented and compared. Clear evidence is presented for two different trap loss mechanisms involving inelastic collisions between one ground state atom and one excited state atom. The fine-structure changing (FSC) mechanism, in which the excited state atom changes fine-structure level during a collision, is seen to dominate the rate at low trap laser intensities. However, as the intensity is increased, the trap becomes sufficiently deep to be able to contain the products of FSC collisions and this mechanism no longer contributes to trap loss. It is a unique aspect of Li that the energy imparted to an atom in a FSC collision is in a range that may be recaptured with experimentally attainable trap parameters. When the products of all FSC collisions remain trapped, only the radiative escape (RE) trap loss mechanism, due to the emission of a less energetic photon than the initial excitation photon, contributes to the trap loss rate. At small detunings, the rate of the RE trap loss mechanism is seen to be over two orders-of-magnitude smaller than the FSC rate. The FSC trap loss rate for $\\sp6$Li and $\\sp7$Li were found to be largest at smaller detunings and of comparable magnitude in $\\sp6$Li and $\\sp7$Li. The RE trap loss rate in $\\sp6$Li was seen to be roughly four times the RE trap loss rate in $\\sp7$Li. To understand better the dynamics of trap loss and magneto-optical traps in general, a sophisticated model of magneto-optical trap kinetics has been developed. This model has demonstrated that most critical factor determining the maximum velocity an atom may have and yet remained trapped is the initial atom's frame detuning, $\\Delta$ - k v, where $\\Delta$ is the trap laser detuning, k is the propagation vector of the trap beam most nearly anti-parallel to v, the atom's velocity. All else being equal, minimizing the magnitude of this quantity maximizes the velocity that a trap will retain. More detailed results of this model are also presented.

Related papers

Collisional loss from a 7 Li magneto-optical trap

Nicholas W. M. Ritchie, E. Abraham, Randall G. Hulet

The process of collisional trap loss in magneto-optically trapped 7Li shows a rich dependence on the depth of the trapping potential, ET. When the trap is shallow enough to allow the escape of atoms with kinetic energy equal to one-half the fine-structure splitting, ΔEfs, fine-structure changing collisions [FS] dominate the collisional trap loss rate. However when the trap is deeper than 1 2 Δ E FS, only the radiative escape mechanism [RE] contributes to trap loss. In this regime, Julienne and Vigue predicted that the collisional loss rate will depend on ET as ~ET-17/6.1 We have measured the collisional loss rate, β, of 7Li from a beam-loaded magneto-optical trap.2 The circles in Fig. 1 show the data for four different trap laser detunings, Δ, and a range of trap laser intensities, 1. The solid line in Fig. 1 is the result of a semi-classical, optical Bloch equation calculation of the RE trap loss rate3 using as input ET, calculated from a truly three-dimensional model.4 The trap depth model predicts that ET is anisotropic. The dashed line in Fig. 1 shows the intensity at which the model predicts E T > 1 2 Δ E FS in all directions, for each detuning. The theory predicts the magnitude of the RE trap loss rate accurately near the point at which the fine structure mechanism turns off, where the trap depth is well known. However at larger detunings and intensities the calculations deviate from the measured values. This suggests that the trap depth model overestimates E, at higher intensities and detunings, or that the trap depth dependence of the RE loss rate deviates from ET-17/6.

•May 8, 1994•0 citations

Trap-loss collisions of ultracold lithium atoms

Nicholas W. M. Ritchie, E. R. I. Abraham, Y. Y. Xiao +3 more

Accurate measurements are presented of the rate of trap-loss-producing collisions between ultracold magneto-optically trapped $^{7}\mathrm{Li}$ atoms for a range of trap laser intensities and frequencies. Intensities from near the atomic saturation intensity to well above it are investigated. At low intensities, fine-structure-changing collisions cause trap loss with a rate constant of \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$/s. At sufficiently high intensity, the trap can be deep enough to effectively freeze out the dominant fine-structure-changing collisions as a loss mechanism, enabling an accurate comparison of the radiative escape loss rate with theory. At the lowest intensities of this radiative escape regime, the measured loss rates compare favorably with those calculated using an optical Bloch equation theory and a three-dimensional model of trap depth. However, the intensity dependence of the measured rates does not show the saturation predicted by the optical Bloch equation theory. It is shown that reliable knowledge of trap depth is necessary to accurately compare experiment with theory.

Physical Review A•Feb 1, 1995•47 citations

Magneto-optical trap and its application to ultra-cold atom collision studies

Yanyang Xiao

We have successfully trapped $\\sp7$Li in a vapor cell magneto-optical trap (MOT). The trap is studied in detail and the parameters are measured from the experiment. The trapping mechanism has been understood in terms of the radiation force and a simple one dimensional model is used in interpreting and predicting the experimental results. The cold-cold atom collision rate coefficient is measured in a beam MOT. The two collision mechanisms, fine structure changing and radiative escape, are discussed in a molecular picture. One of the channels, the fine structure changing channel, can be turned on and off by the experimental conditions, namely the laser intensity in this experiment. The rate coefficient for each mechanism has been determined from the experiment.

•Jan 1, 1994•0 citations

Measurement of fine-structure changing collision in ultracold /sup 85/Rb held in a MOT

Luís Gustavo Marcassa, R. Zanon, Vanderlei Salvador Bagnato +3 more

Summary form only given. In a magneto-optical trap (MOT) two main mechanisms contribute to the total trap loss rate. Radiative escape (RE), where the spontaneous emission within the collision duration transforms internal energy into kinetic motion. Fine-structure changing collision (FSC) is an exoergic process where a pair of excited ground state atoms undergoes a change to the lower state of the fine-structure doublet, followed by a release of /spl Delta/E/sub FSC//2 in kinetic energy normally enough to eject the atoms from the trap. In earlier experiments only the total trap loss rate, which is the sum of contributions from RE and FSC, was determined. Distinguishing between these two mechanisms is important because it allows a more precise comparison with the theory, leading to a better understanding of exoergic cold collisions. In this experiment the FSC contribution to the total loss in /sup 85/Rb is measured by direct photoionization of the P/sub 1/2/ fragments.

Quantum Electronics and Laser Science Conference•Jan 20, 2003•0 citations

Measurement of the collisional trap loss rate in magneto-optically trapped {sup 7}Li and {sup 6}Li

Nicholas W. M. Ritchie, Yangyang Xiao, E. Abraham +1 more

Collisions between ultra-cold (T << 1K) atoms confined in a magneto- optical trap (MOT) may result in the ejection of atoms from the trap. These collisional loss processes, which involve ground state/excited state collisions, fundamentally limit the density attainable in MOT traps. Although accurate calculations of collision rates between ultra-cold atoms require precise knowledge of the molecular potentials over a long range, the loss rate for Li was recently predicted to be significantly less than for the other alkali metals. Motivated by this result, we are measuring the collisional loss rate of Li in a vapor-cell MOT using a red-detuned laser beam to catalyze the collisions, similar to recent experiments using Rb and Cs. We will report our progress to measure the trap loss rate for {sup 6}Li and {sup 7}Li, which will be compared to investigate an isotopic dependence, as was recently observed for Rb.

Bulletin of the American Physical Society•May 1, 1993•0 citations

Cold inelastic collisions between lithium and cesium in a two-species magneto-optical trap

Schlöder, U, Engler, H, Schünemann, U +2 more

We investigate collisional properties of lithium and cesium which are simultaneously confined in a combined magneto-optical trap. Trap-loss collisions between the two species are comprehensively studied. Different inelastic collision channels are identified, and inter-species rate coefficients as well as cross sections are determined. It is found that loss rates are independent of the optical excitation of Li, as a consequence of the repulsive Li$^*$-Cs interaction. Li and Cs loss by inelastic inter-species collisions can completely be attributed to processes involving optically excited cesium (fine-structure changing collisions and radiative escape). By lowering the trap depth for Li, an additional loss channel of Li is observed which results from ground-state Li-Cs collisions changing the hyperfine state of cesium.

•Jan 1, 1999•28 citations
Measurements of the trap loss rate in ultra-cold magneto-optically trapped sp6\\sp6sp6Li and sp7\\sp7sp7Li are presented and compared. Clear evidence is presented for two different trap loss mechanisms involving inelastic collisions between one ground state atom and one excited state atom. The fine-structure changing (FSC) mechanism, in which the excited state atom changes fine-structure level during a collision, is seen to dominate the rate at low trap laser intensities. However, as the intensity is increased, the trap becomes sufficiently deep to be able to contain the products of FSC collisions and this mechanism no longer contributes to trap loss. It is a unique aspect of Li that the energy imparted to an atom in a FSC collision is in a range that may be recaptured with experimentally attainable trap parameters. When the products of all FSC collisions remain trapped, only the radiative escape (RE) trap loss mechanism, due to the emission of a less energetic photon than the initial excitation photon, contributes to the trap loss rate. At small detunings, the rate of the RE trap loss mechanism is seen to be over two orders-of-magnitude smaller than the FSC rate. The FSC trap loss rate for sp6\\sp6sp6Li and sp7\\sp7sp7Li were found to be largest at smaller detunings and of comparable magnitude in sp6\\sp6sp6Li and sp7\\sp7sp7Li. The RE trap loss rate in sp6\\sp6sp6Li was seen to be roughly four times the RE trap loss rate in sp7\\sp7sp7Li. To understand better the dynamics of trap loss and magneto-optical traps in general, a sophisticated model of magneto-optical trap kinetics has been developed. This model has demonstrated that most critical factor determining the maximum velocity an atom may have and yet remained trapped is the initial atom's frame detuning, Delta\\DeltaDelta - k v, where Delta\\DeltaDelta is the trap laser detuning, k is the propagation vector of the trap beam most nearly anti-parallel to v, the atom's velocity. All else being equal, minimizing the magnitude of this quantity maximizes the velocity that a trap will retain. More detailed results of this model are also presented.
The process of collisional trap loss in magneto-optically trapped 7Li shows a rich dependence on the depth of the trapping potential, ET. When the trap is shallow enough to allow the escape of atoms with kinetic energy equal to one-half the fine-structure splitting, ΔEfs, fine-structure changing collisions [FS] dominate the collisional trap loss rate. However when the trap is deeper than 1 2 Δ E FS, only the radiative escape mechanism [RE] contributes to trap loss. In this regime, Julienne and Vigue predicted that the collisional loss rate will depend on ET as ~ET-17/6.1 We have measured the collisional loss rate, β, of 7Li from a beam-loaded magneto-optical trap.2 The circles in Fig. 1 show the data for four different trap laser detunings, Δ, and a range of trap laser intensities, 1. The solid line in Fig. 1 is the result of a semi-classical, optical Bloch equation calculation of the RE trap loss rate3 using as input ET, calculated from a truly three-dimensional model.4 The trap depth model predicts that ET is anisotropic. The dashed line in Fig. 1 shows the intensity at which the model predicts E T > 1 2 Δ E FS in all directions, for each detuning. The theory predicts the magnitude of the RE trap loss rate accurately near the point at which the fine structure mechanism turns off, where the trap depth is well known. However at larger detunings and intensities the calculations deviate from the measured values. This suggests that the trap depth model overestimates E, at higher intensities and detunings, or that the trap depth dependence of the RE loss rate deviates from ET-17/6.
Accurate measurements are presented of the rate of trap-loss-producing collisions between ultracold magneto-optically trapped 7Li^{7}\mathrm{Li}7Li atoms for a range of trap laser intensities and frequencies. Intensities from near the atomic saturation intensity to well above it are investigated. At low intensities, fine-structure-changing collisions cause trap loss with a rate constant of \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}10}$ cm3{\mathrm{cm}}^{3}cm3/s. At sufficiently high intensity, the trap can be deep enough to effectively freeze out the dominant fine-structure-changing collisions as a loss mechanism, enabling an accurate comparison of the radiative escape loss rate with theory. At the lowest intensities of this radiative escape regime, the measured loss rates compare favorably with those calculated using an optical Bloch equation theory and a three-dimensional model of trap depth. However, the intensity dependence of the measured rates does not show the saturation predicted by the optical Bloch equation theory. It is shown that reliable knowledge of trap depth is necessary to accurately compare experiment with theory.
We have successfully trapped sp7\\sp7sp7Li in a vapor cell magneto-optical trap (MOT). The trap is studied in detail and the parameters are measured from the experiment. The trapping mechanism has been understood in terms of the radiation force and a simple one dimensional model is used in interpreting and predicting the experimental results. The cold-cold atom collision rate coefficient is measured in a beam MOT. The two collision mechanisms, fine structure changing and radiative escape, are discussed in a molecular picture. One of the channels, the fine structure changing channel, can be turned on and off by the experimental conditions, namely the laser intensity in this experiment. The rate coefficient for each mechanism has been determined from the experiment.
Summary form only given. In a magneto-optical trap (MOT) two main mechanisms contribute to the total trap loss rate. Radiative escape (RE), where the spontaneous emission within the collision duration transforms internal energy into kinetic motion. Fine-structure changing collision (FSC) is an exoergic process where a pair of excited ground state atoms undergoes a change to the lower state of the fine-structure doublet, followed by a release of /spl Delta/E/sub FSC//2 in kinetic energy normally enough to eject the atoms from the trap. In earlier experiments only the total trap loss rate, which is the sum of contributions from RE and FSC, was determined. Distinguishing between these two mechanisms is important because it allows a more precise comparison with the theory, leading to a better understanding of exoergic cold collisions. In this experiment the FSC contribution to the total loss in /sup 85/Rb is measured by direct photoionization of the P/sub 1/2/ fragments.
Collisions between ultra-cold (T << 1K) atoms confined in a magneto- optical trap (MOT) may result in the ejection of atoms from the trap. These collisional loss processes, which involve ground state/excited state collisions, fundamentally limit the density attainable in MOT traps. Although accurate calculations of collision rates between ultra-cold atoms require precise knowledge of the molecular potentials over a long range, the loss rate for Li was recently predicted to be significantly less than for the other alkali metals. Motivated by this result, we are measuring the collisional loss rate of Li in a vapor-cell MOT using a red-detuned laser beam to catalyze the collisions, similar to recent experiments using Rb and Cs. We will report our progress to measure the trap loss rate for {sup 6}Li and {sup 7}Li, which will be compared to investigate an isotopic dependence, as was recently observed for Rb.
We investigate collisional properties of lithium and cesium which are simultaneously confined in a combined magneto-optical trap. Trap-loss collisions between the two species are comprehensively studied. Different inelastic collision channels are identified, and inter-species rate coefficients as well as cross sections are determined. It is found that loss rates are independent of the optical excitation of Li, as a consequence of the repulsive Li∗^*∗-Cs interaction. Li and Cs loss by inelastic inter-species collisions can completely be attributed to processes involving optically excited cesium (fine-structure changing collisions and radiative escape). By lowering the trap depth for Li, an additional loss channel of Li is observed which results from ground-state Li-Cs collisions changing the hyperfine state of cesium.