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Quasithermalization of collisionless particles in quadrupole potentials

Quasithermalization of collisionless particles in quadrupole potentials
Quasithermalization of collisionless particles in quadrupole potentials
We analyze several puzzling features of a recent experiment with a noninteracting gas of atoms in a quadrupole trap. After an initial momentum kick, the system reaches a stationary, quasi-thermal state even without collisions, due to the dephasing of individual particle trajectories. Surprisingly, the momentum distribution remains anisotropic at long times, characterized by different “temperatures” along the different directions. In particular, there is no transfer of the kick energy between the axial and radial trap directions. To understand these effects we discuss and solve two closely related models: a spherically symmetric trap V(r)rα and a strongly confined gas along one direction (a “pancake” trap). We find that in the isotropic trap, the gas unexpectedly also preserves the anisotropy of the kick at long times, which we are able to explain using the conservation of angular momentum and the virial theorem. Depending on the value of α we find that the kick can cool or heat the orthogonal directions. The pancake trap case is quantitatively similar to the quadrupole one. We show that for the former, the temperature anisotropy and memory of the kick direction are due to the change in the 2D effective potential resulting from the kick, thereby also explaining the quadrupole experimental results.
1050-2947
1-15
Lau, Johnathan
d4b0ceb2-fe6a-4d15-83d9-0e03a7ad4756
Goulko, Olga
0191198d-3ec7-42e9-8e07-0b6f878d6ebd
Reimann, Thomas
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Suchet, Daniel
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Enesa, Cédric
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Chevy, Frédéric
6ba4ec21-58c0-48f7-b2b1-08417aa16273
Lobo, Carlos
cde7843a-c00b-4242-a8cd-1abb2dfe0703
Lau, Johnathan
d4b0ceb2-fe6a-4d15-83d9-0e03a7ad4756
Goulko, Olga
0191198d-3ec7-42e9-8e07-0b6f878d6ebd
Reimann, Thomas
932c3357-1657-4c8c-86f2-34836597ece1
Suchet, Daniel
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Enesa, Cédric
a93fede7-099e-4a68-9b8c-3edb1fb44465
Chevy, Frédéric
6ba4ec21-58c0-48f7-b2b1-08417aa16273
Lobo, Carlos
cde7843a-c00b-4242-a8cd-1abb2dfe0703

Lau, Johnathan, Goulko, Olga, Reimann, Thomas, Suchet, Daniel, Enesa, Cédric, Chevy, Frédéric and Lobo, Carlos (2020) Quasithermalization of collisionless particles in quadrupole potentials. Physical Review A, 101 (3), 1-15, [033605]. (doi:10.1103/PhysRevA.101.033605).

Record type: Article

Abstract

We analyze several puzzling features of a recent experiment with a noninteracting gas of atoms in a quadrupole trap. After an initial momentum kick, the system reaches a stationary, quasi-thermal state even without collisions, due to the dephasing of individual particle trajectories. Surprisingly, the momentum distribution remains anisotropic at long times, characterized by different “temperatures” along the different directions. In particular, there is no transfer of the kick energy between the axial and radial trap directions. To understand these effects we discuss and solve two closely related models: a spherically symmetric trap V(r)rα and a strongly confined gas along one direction (a “pancake” trap). We find that in the isotropic trap, the gas unexpectedly also preserves the anisotropy of the kick at long times, which we are able to explain using the conservation of angular momentum and the virial theorem. Depending on the value of α we find that the kick can cool or heat the orthogonal directions. The pancake trap case is quantitatively similar to the quadrupole one. We show that for the former, the temperature anisotropy and memory of the kick direction are due to the change in the 2D effective potential resulting from the kick, thereby also explaining the quadrupole experimental results.

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More information

Accepted/In Press date: 30 October 2019
e-pub ahead of print date: 9 March 2020
Published date: March 2020

Identifiers

Local EPrints ID: 435687
URI: http://eprints.soton.ac.uk/id/eprint/435687
ISSN: 1050-2947
PURE UUID: a1c33c97-e724-4c94-a795-2246b656e02d
ORCID for Carlos Lobo: ORCID iD orcid.org/0000-0001-7060-3905

Catalogue record

Date deposited: 18 Nov 2019 17:30
Last modified: 26 Nov 2021 02:54

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Contributors

Author: Johnathan Lau
Author: Olga Goulko
Author: Thomas Reimann
Author: Daniel Suchet
Author: Cédric Enesa
Author: Frédéric Chevy
Author: Carlos Lobo ORCID iD

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