The role of the Pauli principle in metastability exchange collisions

Pinard, M.; Laloë, Franck

doi:10.1051/jphys:01980004108079900

Cited by 11 publications

(11 citation statements)

References 20 publications

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“…are spins [25]. Introducing density operators ρ g and ρ m to characterise the spin states of colliding ground state and metastable state atoms, respectively, a ME collision where excitation is exchanged between colliding atoms can be described as:…”

Section: Metastability Exchange and Spin-temperature Distributionmentioning

confidence: 99%

Fundamentals of metastability exchange optical pumping in helium

Batz

Nacher

Tastevin

2011

J. Phys.: Conf. Ser.

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Section: Metastability Exchange and Spin-temperature Distributionmentioning

confidence: 99%

Fundamentals of metastability exchange optical pumping in helium

Batz

Nacher

Tastevin

2011

J. Phys.: Conf. Ser.

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“…(Jk (8) We shaU use here a definition of the scalar product whicJl differs froID the definition in the preceding appendix. Our definition is now :…”

Section: Bp(p) = (P?)-1/2 Bps(p)(p~)-1/2mentioning

confidence: 99%

“…e) If Qr = 4 n (ail atoms detected), one Ganshow [Ref. [8], § 2.2. 2J that A( 4 n) = 1, CC 4 n) = 0; ail particle indistinguishability effects disappear and Pr(4 n) = Pl + pz.…”

Section: N°2mentioning

confidence: 99%

“…We first ( § 1) give a detailed sindy of a binary collision, recalling the results already obtained in the Appendix Il of a preceding article [8]; we discuss the interference effects introduced by particle indistinguishability, and see how they may affect the nuclear spin orientation.. ln terms of spin density opera tors, these effects are described by anticommutators and cz) An analoguous situation holds for a classical mixture of two gases A and B, where the concentration current is not directly affected by collisions between atolls of the saille species; thus, the diffusion coefficient D depends on the cross section OE ABfor collision between atolls A and B, but not on (JAAor OEBB (when small corrections are neglected). { commutators, the latter introducing the «identical spin rotation effect ».…”

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confidence: 99%

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Transport properties in a spin polarized gas, I

1982

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Résumé.-On étudie l'influencedes effetsd'indiscernabilitédes atomes sur les propriétés de transport dans un gaz orienté à basse température, 3HeÎ par exemple, le gaz étant supposé dilué et donc non dégénéré. Dans ce but, on commence par étudier en détail ces effets dans une collision binaire; bien que l'on néglige toute interaction agissant sur les spins pendant la collision, on constate que des effets d'interférence quantique peuvent conduire à des changements de leur orientation (effets de rotation de spins identiques). Dans une seconde étape, on écrit une équation de Boltzmann satisfaite par un opérateur densité de spin ps(r, p), qui joue un rôle analogue à la fonction de distribution classique de Boltzmann f(r, p), et peut être obtenu par transformation de Wigner de l'opé-rateur densité à une particule; dans cette équation, les effets d'indiscernabilité introduisent trois nouvelles « sections efficaces» indépendantes, alors que le terme classique ne dépend que d'une seule. L'application de la méthode de Chapman-Enskog à l'ordre le plus bas introduit alors un opérateur linéaire de collision Fe qui dépend explicitement de l'orientation M du gaz; en particulier, si M n'est pas nul, Fe n'est pas hermitique. Enfin, les résultats précédents sont appliqués à deux cas particuliers,conduction de la chaleur et viscosité, et l'on obtient la dépendance des coefficients correspondants en fonction de M. Cette dépendance peut être très marquée à basse température. Dans l'article qui suit celui-ci, on étudie le problème de la diffusion de spin et l'on prédit un certain nombre d'effets quantiques dus à l'indiscernabilité des particules: équation de diffusion anisotrope, non linéaire, couPlage avec un gradient thermique.Abstract. -The transport properties of a spin polarized gag at low temperature eHeÎ for instance)are studied, the emphasis being put on the particle indistinguishability effects during collisions; the gas is dilute and no degeneracy effects occur. We first study in detail the,partic1e indistinguishability effects in a binary collision and, although all interactions involving the spins are completely ignored during the collision time, we note that interference effects can lead to a change of the spin directions «< identical spin rotation effect »). From this study, we obtain the collision term of a Boltzmann equation for a spin operator ps(r, p), which is the analogue of a classical Boltzmann distribution function fer, p), and can be obtained by a Wigner transform -with respect to the orbital variables -of the one particle density operator; in this Boltzmann equation, in addition to the classical term which depends on one cross section, several terms arise from partic1e indistinguishability effects and introduce 3 other, independent, «cross sections ». The c1assical Chapman-Enskog approximation is then used and a linearized collision operator Fe is 0btained ; r cdepends on the spin polarization M in the gas and, if Mis not zero, r c is not a Hermitian operator. Final1y, the preceding results are applied to two ...

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“…3 S state atoms we shall use a standard density operator formalism and extend the treatment introduced by Partridge and Series [44] for ME collisions, later improved [45,46] and used for an OP model [7], to the case of an arbitrary magnetic field. Our first goal is to show that the "spin temperature" concept [47,48,7] remains valid, and that the population distribution in the 2 3 S state is fully determined (in the absence of OP and of relaxation) by the nuclear polarisation M of the ground state.…”

Section: Metastability Exchangementioning

confidence: 99%

Magnetic field effects on the 1 083 nm atomic line of helium

Courtade¹,

Marion²,

Nacher³

et al. 2002

The European Physical Journal D - Atomic, Molecular and Optical

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Abstract. The structure of the excited 2 3 S and 2 3 P triplet states of 3 He and 4 He in an applied magnetic field B is studied using different approximations of the atomic Hamiltonian. All optical transitions (line positions and intensities) of the 1083 nm 2 3 S-2 3 P transition are computed as a function of B. The effect of metastability exchange collisions between atoms in the ground state and in the 2 3 S metastable state is studied, and rate equations are derived, for the populations these states in the general case of an isotopic mixture in an arbitrary field B. It is shown that the usual spin-temperature description remains valid. A simple optical pumping model based on these rate equations is used to study the B-dependence of the population couplings which result from the exchange collisions. Simple spectroscopy measurements are performed using a single-frequency laser diode on the 1083 nm transition. The accuracy of frequency scans and of measurements of transition intensities is studied. Systematic experimental verifications are made for B=0 to 1.5 T. Optical pumping effects resulting from hyperfine decoupling in high field are observed to be in good agreement with the predictions of the simple model. Based on adequately chosen absorption measurements at 1083 nm, a general optical method to measure the nuclear polarisation of the atoms in the ground state in an arbitrary field is described. It is demonstrated at B ∼0

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The role of the Pauli principle in metastability exchange collisions

Cited by 11 publications

References 20 publications

Fundamentals of metastability exchange optical pumping in helium

Fundamentals of metastability exchange optical pumping in helium

Transport properties in a spin polarized gas, I

Magnetic field effects on the 1 083 nm atomic line of helium

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