Table of Contents
Research Letters in Physics
VolumeΒ 2008, Article IDΒ 570167, 4 pages
http://dx.doi.org/10.1155/2008/570167
Research Letter

Quantum Transitions by Change of Parameters and in Noninertial Motion

Department of Theoretical Physics, Institute of Atomic Physics, Magurele, 077125 Bucharest, Romania

Received 1 October 2007; Accepted 13 February 2008

Academic Editor: JerryΒ Draayer

Copyright Β© 2008 M. Apostol. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

As it is well known, a quantum system depending on parameters exhibits the (geometric) Berry phase when parameters are varying in the adiabatic limit. A generalization of the Berry phase is given in the present paper for a nonadiabatic change of parameters, which leads to quantum transitions in the system. This generalization is applied to noninertial motions and it is shown that such motions may induce quantum transitions for a system in an external field governed by Schrodinger's equation.

1. Introduction

As it is well known [1], a quantum system subjected to a change of parameters exhibits the (geometric) Berry phase, providing the change proceeds in the adiabatic limit. A careful examination of the derivation of the Berry phase suggests that a nonadiabatic change in parameters may induce quantum transitions in the system. It is shown in the present paper that the Berry phase can be generalized in such a way as to describe quantum transitions for such nonadiabatic changes in parameters. Moreover, it is shown that the displacement vector in a (nonuniform) translation or the rotation angle in a (nonuniform) rotation may play the role of such nonadiabatic parameters, such that a noninertial motion may cause quantum transitions for a system placed in an external field.

2. Berry Phase

Let the hamiltonian 𝐻, its (orthogonal) eigenfunctions πœ‘π‘˜, and energy eigenvalues πΈπ‘˜ depend on a parameter denoted generically by 𝐑. This dependence is written explicitly in the eigenvalue equation𝐻(𝐑)πœ‘π‘˜(𝐑)=πΈπ‘˜(𝐑)πœ‘π‘˜(𝐑).(1)A time dependence 𝐑(𝑑) is assumed for the parameter 𝐑, and Schrodinger's equation is written asπ‘–β„πœ•πœ“(𝑑)πœ•π‘‘=𝐻(𝐑)πœ“(𝑑).(2)In the adiabatic limit ̇𝐑→0, the original eigenstate πœ‘π‘›(𝐑) is preserved during the temporal evolution, and the solution of (2) readsπœ“π‘›ξ‚ƒβˆ’π‘–(𝑑)=expβ„ξ€œπ‘‘0𝐸𝑛𝐑(π‘‘ξ…ž)ξ‚π‘‘π‘‘ξ…žξ‚„β‹…π‘’π‘–π›Ύπ‘›(𝑑)πœ‘π‘›ξ‚€ξ‚,𝐑(𝑑)(3)where 𝛾𝑛(𝑑) is given byΜ‡π›Ύπ‘›ξ‚€πœ‘(𝑑)=𝑖𝑛,πœ•πœ‘π‘›ξ‚Μ‡πœ•π‘π‘.(4)The bracket in (4) indicates a scalar (inner) product. For a circuit 𝐢 described by the parameter 𝐑, this is Berry's geometric phase 𝛾𝑛 [1].

3. Transitions by Change of Parameters

This result implies that, in general, for nonvanishing ̇𝐑, the quantum system may exhibit transitions between its various states. Indeed, the general solution of (2) can be written asξ“πœ“(𝑑)=π‘˜π‘Žπ‘˜ξ‚ƒβˆ’π‘–(𝑑)expβ„ξ€œπ‘‘0πΈπ‘˜ξ‚€π‘(π‘‘ξ…ž)ξ‚π‘‘π‘‘ξ…žξ‚„πœ‘π‘˜ξ‚€ξ‚π‘(𝑑),(5)where the coefficients π‘Žπ‘˜(𝑑) obey the equationΜ‡π‘Žπ‘›ξ“=π‘–π‘˜π‘Žπ‘˜π›Ύπ‘›π‘˜Μ‡π‘ξ‚ƒπ‘–(𝑑)β‹…expβ„ξ€œπ‘‘0𝐸𝑛𝐑(π‘‘ξ…ž)ξ‚βˆ’πΈπ‘˜ξ‚€π‘(π‘‘ξ…ž)ξ‚ξ‚„π‘‘π‘‘ξ…žξ‚„,𝛾(6)π‘›π‘˜ξ‚€πœ‘(𝑑)=𝑖𝑛,πœ•πœ‘π‘˜ξ‚.πœ•π‘(7)

This π›Ύπ‘›π‘˜(𝑑) is a generalization of the Berry phase; the latter corresponds toπ›Ύπ‘›ξ€œ(𝑑)=𝑑0𝑑𝐑(π‘‘ξ…ž)𝛾𝑛𝑛(π‘‘ξ…ž),(8)where the integration is performed along the path described by the parameter 𝐑 in its motion from 𝐑(𝑑=0) to 𝐑(𝑑). The π›Ύπ‘›π‘˜(𝑑) are the matrix elements of the operator βˆ’π/ℏ, π›Ύπ‘›π‘˜=βˆ’ππ‘›π‘˜/ℏ, where 𝐏 may be viewed formally as the momentum associated with the parameter 𝐑. Then (6) gives the transition amplitudes caused by a perturbation 𝐻1=𝐕𝐏, where ̇𝐑𝐕= is the velocity of the parameter 𝐑.

Equation (6) is solved in the first order of the perturbation theory, with the initial conditions π‘Žπ‘›(0)=1, π‘Žπ‘˜(0)=0 for π‘˜β‰ π‘›. The transition amplitudesπ‘Žπ‘˜π‘›ξ€œ(𝑑)=𝑖𝑑0𝑑𝐑(π‘‘ξ…ž)π›Ύπ‘˜π‘›(π‘‘ξ…ž)𝑖⋅expβ„ξ€œπ‘‘β€²0ξ‚ƒπΈπ‘˜ξ‚€π‘(π‘‘ξ…žξ…ž)ξ‚βˆ’πΈπ‘›ξ‚€π‘(π‘‘ξ…žξ…ž)ξ‚ξ‚„π‘‘π‘‘ξ…žξ…žξ‚„(9)are obtained, where an additional label π‘˜ has been given to the coefficient π‘Žπ‘› in order to indicate the transition from state 𝑛 to state π‘˜. At the same time,π‘Žπ‘›π‘›ξ€œ(𝑑)=1+𝑖𝑑0𝑑𝐑(π‘‘ξ…ž)𝛾𝑛𝑛(π‘‘ξ…ž)=1+𝑖𝛾𝑛(𝑑).(10)From (9) and (10), one can see that in the adiabatic limit ̇𝐑→0 the Berry phase 𝛾𝑛=𝛾𝑛(𝑇) is recovered in π‘Žπ‘›π‘›(𝑇)=𝑒𝑖𝛾𝑛(𝑇) for a circuit 𝐢, where 𝑇 is the period during which the parameter 𝐑 describes the circuit 𝐢.

In the first order of the perturbation theory, the 𝐑-dependence of the matrix elements π›Ύπ‘˜π‘› and energy eigenvalues in the exponential factor in (9) may be neglected. The transition amplitudes can then be written asπ‘Žπ‘˜π‘›π‘–(𝑑)=βˆ’β„ξ€œπ‘‘0π‘‘π‘‘ξ…žβ‹…π•(π‘‘ξ…ž)ππ‘˜π‘›ξ‚€expπ‘–πœ”π‘˜π‘›π‘‘ξ…žξ‚,(11)where πœ”π‘˜π‘›(𝑑)=(πΈπ‘˜βˆ’πΈπ‘›)/ℏ.

For a uniform change of parameters, that is, for 𝐕 = const, the transition amplitudes are vanishing (π‘Žπ‘˜π‘›(𝑑)=0, π‘˜β‰ π‘›). The diagonal amplitude π‘Žπ‘›π‘›(𝑑)=1βˆ’(𝑖/ℏ)𝐕𝐏𝑛𝑛𝑑≃exp(βˆ’π‘–π•ππ‘›π‘›π‘‘/ℏ) given by (10) contains the correction 𝐕𝐏𝑛𝑛 to the energy of the state πœ‘π‘› in the first order of the perturbation theory. The gauge transformation πœ“ξ…žπ‘›=exp(βˆ’π‘–π•ππ‘›π‘›π‘‘/ℏ)πœ“π‘› leaves Schrodinger's equation unchanged.

Let velocity 𝐕 have a sudden variation from 𝐕=0 for 0<𝑑<𝑑0 to 𝐕 = const for 𝑑0<𝑑, such that πœ•π•/πœ•π‘‘=𝐕𝛿(π‘‘βˆ’π‘‘0). The transition amplitudes given by (11) becomeπ‘Žπ‘˜π‘›(𝑑)=βˆ’π•ππ‘˜π‘›π‘’π‘–πœ”π‘˜π‘›π‘‘πΈπ‘˜βˆ’πΈπ‘›+ξ‚ƒπ•ππ‘˜π‘›πΈπ‘˜βˆ’πΈπ‘›ξ‚„π‘’π‘–(πΈπ‘˜βˆ’πΈπ‘›)𝑑0/ℏ.(12)The first term in the rhs of this equation corresponds to the change in the wave function under the action of the constant perturbation 𝐕𝐏 for 𝑑>𝑑0. The transition amplitude is given by the second term in the rhs of (12), so the transition probability is π‘€π‘˜π‘›=[π•ππ‘˜π‘›/(πΈπ‘˜βˆ’πΈπ‘›)]2.

If the velocity is periodic in time with frequency πœ”, 𝐕(𝑑)=π•π‘’π‘–πœ”π‘‘+c.c., the transition probability per unit time is given by π‘€π‘˜π‘›=(2πœ‹/ℏ)(π•ππ‘˜π‘›)2𝛿(πΈπ‘˜βˆ’πΈπ‘›Β±β„πœ”) in the limit of the infinite time. The calculations are not restricted to the discrete spectrum, so there may appear transitions in the continuum. It is worth noting that frequencies πœ” in the variation spectrum of the parameter 𝐑 must be comparatively high of the order of the frequencies of the quantum system in order to have such quantum transitions. For a quantum-statistical system with a characteristic spectrum β„πœ”Γ—integer, the quantum transitions described above may induce an increase π›Ώπ‘‡βˆΌβ„πœ” in temperature. For a periodic change of parameters, the frequency πœ” is proportional to the ratio of the average acceleration π‘Ž to the average velocity 𝑣, so the increase in temperature is π›Ώπ‘‡βˆΌβ„π‘£/π‘Ž. It is similar with the Unruh temperature [2].

4. Some Simple Applications

Let a particle of mass π‘š move in an infinite square potential well in one dimension. The eigenfunctions are πœ‘π‘›βˆš(π‘₯)=2/π‘Žsin(πœ‹π‘›π‘₯/π‘Ž) and the energy eigenvalues are given by 𝐸𝑛=πœ‹2ℏ2𝑛2/2π‘šπ‘Ž2, where 𝑛=1,2,…. The width π‘Ž of this potential well is taken as parameter 𝑅. The wall of the potential well, placed at distance π‘Ž from the origin, is subjected to an oscillatory motion of frequency πœ” as described by π‘Ž=π‘Ž0+πœ€cosπœ”π‘‘, where πœ€/π‘Ž0β‰ͺ1. Making use of (11), we get the transition probabilities π‘€π‘˜π‘›=2πœ‹β„[πœ€πœ”π‘˜π‘›/π‘Ž0(π‘˜2βˆ’π‘›2)]2𝛿(πΈπ‘˜βˆ’πΈπ‘›Β±β„πœ”) per unit time in the limit of the infinite time. The diagonal matrix element 𝛾𝑛𝑛 is vanishing in this case, 𝛾𝑛𝑛=0.

Following Berry [1], we consider a spin 𝐒 placed in a magnetic field 𝐁. The hamiltonian reads 𝐻=βˆ’π‘”πœ‡ππ’, where 𝑔 is the gyromagnetic factor and πœ‡ is the Bohr magneton. The energy eigenvalues are given by 𝐸𝑛=βˆ’π‘”πœ‡π΅π‘›, where 𝑛=βˆ’π‘†,…,𝑆. In order to calculate the matrix elements entering (11), it is convenient to use the identity (πΈπ‘›βˆ’πΈπ‘˜)(πœ‘π‘˜,πœ•πœ‘π‘›/πœ•π‘)=(πœ‘π‘˜,(πœ•π»/πœ•π‘)πœ‘π‘›) for π‘˜β‰ π‘›. We write then 𝐁𝐒=𝐡(𝑆π‘₯sinπœƒcosπœ™+𝑆𝑦sinπœƒsinπœ™+𝑆𝑧cosπœƒ) and take the angles πœƒ and πœ™ as parameters 𝑅. First, we set πœ™=0 and let πœƒ describe a circuit according to πœƒ=πœ”π‘‘, where πœ”β‰ͺπ‘”πœ‡π΅/ℏ. Making use of (9), we get transition probabilities π‘€π‘˜π‘›=(πœ‹β„πœ”2/8) in the limit of the infinite time. Since [𝑆(𝑆+1)βˆ’π‘›(𝑛±1)]π›Ώπ‘˜,𝑛±1𝛿(πΈπ‘›βˆ’πΈπ‘˜Β±β„πœ”), these transition probabilities are vanishing, in fact, as we get by using (11). We may also set πœ”β‰ͺπ‘”πœ‡π΅/ℏ = const and let πœƒ describe a conical circuit of semiangle πœ™=πœ”π‘‘. The results are similar, the amplitudes containing now the factor πœƒ.

Another example is provided by the electronic terms of the molecules, which depend parametrically on the nuclear coordinates sinπœƒ. The interaction 𝐑 can easily be estimated as 𝐻1=𝐕𝐏, where 𝐻1∼(π‘š/𝑀)𝐸el is a characteristic electronic term of the molecule and 𝐸el is the ratio of the electron mass π‘š/𝑀 to the nuclear mass π‘š. It is of the same order of magnitude as the accuracy of the adiabatic decoupling of the electronic motion from the nuclear motion, so it gives a natural width of the electronic terms in molecules.

5. Noninertial Motion Translations

A similar analysis can be carried out for noninertial motion. Let 𝑀, 𝐫=π«ξ…ž+𝐑(π‘‘ξ…ž), be a translation, where 𝑑=π‘‘ξ…ž, 𝐫 denote the position of the system and π«ξ…ž is the displacement vector. The hamiltonian, its eigenfunctions, and energy eigenvalues do not depend on the displacement 𝐑, so it can be taken as the general parameter 𝐑 in the previous sections. Schrodinger's (2) becomes𝐑where π‘–β„πœ•πœ“(π‘‘ξ…ž,π«ξ…ž)πœ•π‘‘ξ…ž=𝐻(π«ξ…ž)πœ“(π‘‘ξ…ž,π«ξ…ž)+π‘–β„π•πœ•πœ“(π‘‘ξ…ž,π‘Ÿξ…ž)πœ•π«ξ…ž,(13). The last term in the rhs of (13) can be viewed as an interaction ̇𝐑𝐕=, where 𝐻1=βˆ’π•π© is the momentum associated to the coordinate 𝑝=βˆ’π‘–β„πœ•/πœ•π«ξ…ž. The transition amplitudes are given by (11), where π«ξ…ž is replaced by 𝐏.

For a free particle, the transition amplitudes are vanishing since 𝐩 for π©π‘˜π‘›=0. Similarly, for an ensemble of (in general interacting) particles, the momentum π‘˜β‰ π‘› is the total momentum, that is, the momentum of the center of mass of the ensemble, so there are no transitions as expected. The coefficient 𝐩 corresponds to a gauge transformation π‘Žπ‘›π‘›(𝑑) of the ∫exp[𝑖𝑑0𝑑𝑑1𝐕(𝑑1)𝐩𝑛𝑛]-state, which, in general, has no determined energy (it is not a stationary state in general). For constant velocity 𝑛 = const, the phase of this gauge transformation is the first-order correction to the energy of the 𝐕-state. It is easy to check that the gauge transformation 𝑛, where πœ“ξ…ž(𝑑,π«ξ…ž)=exp[βˆ’(𝑖/ℏ)(𝑀𝑉2𝑑/2+𝑀𝐕𝐫)]πœ“(𝑑,𝐫) is the mass of the ensemble, preserves Schrodinger's equation in accordance with Galileo's principle of relativity. The unitary transformation 𝑀 takes the Schrodinger equation πœ“=exp(βˆ’π‘–π‘π©/ℏ)πœ“ξ…ž into π‘–β„πœ•πœ“/πœ•π‘‘=π»πœ“. Making use of π‘–β„πœ•πœ“ξ…ž/πœ•π‘‘=π»πœ“βˆ’π•π©πœ“ξ…ž+𝐑(πœ•π»/πœ•π«)πœ“ξ…ž+β‹― one can show by direct calculation that the additional interacting term in the hamiltonian has no relevance. Such a unitary transformation is different from the coordinate change.

The situation is different for particles in an external field. There, in general, the offdiagonal matrix elements (πœ‘π‘˜,(πœ•π»/πœ•π«)πœ‘π‘›)=(πΈπ‘›βˆ’πΈπ‘˜)(πœ‘π‘˜,πœ•πœ‘π‘›/πœ•π«), of the momentum of the particles are nonvanishing, and they may cause transitions. For instance, if one or more particles in an ensemble of interacting particles acquire a large mass, then they may be viewed as being at rest during the motion of the rest of particles. Their interaction with the rest of particles becomes now an external field for the latter, whose motion depends parametrically on the positions of the former. The coordinates of the heavy particles do not appear anymore in the momentum, so there may exist nonvanishing matrix elements of this momentum between states of the moving particles. It follows that noninertial motion may give rise to quantum transitions for particles in an external field.

6. Noninertial Motion Rotations

A similar result holds also for rotations. Let π©π‘˜π‘›, π‘Ÿπ‘–=𝛼𝑖𝑗(π‘‘ξ…ž)π‘Ÿπ‘—, be a change of coordinates (𝑑=π‘‘ξ…ž), where 𝑖,𝑗=1,2,3 is a rotation matrix of angle 𝛼𝑖𝑗 and angular velocity πœ™ about some axis, such that Μ‡πœ™=𝛀, π‘Ÿξ…žπ‘–=𝛼𝑗𝑖(𝑑)π‘Ÿπ‘—. Making use of π›Όπ‘—π‘–π›Όπ‘—π‘˜=π›Ώπ‘–π‘˜, where 𝛼𝑙𝑖̇𝛼𝑙𝑗=πœ€π‘–π‘—π‘˜Ξ©π‘˜ is the totally antisymmetric unit tensor, we get easily that an interaction πœ€π‘–π‘—π‘˜ appears in hamiltonian, similar with the interaction given by (13), where 𝐻1=𝛀π₯ is the total (orbital) angular momentum. The parameter π₯ introduced in the previous sections is the rotation angle 𝐑 in this case. The discussion is similar with the one given above for translations. For a free particle, or an ensemble of interacting particles, the total angular momentum has no offdiagonal matrix elements. The coefficient πœ™ may generate a gauge transformation, which reflects, in general, the nonstationarity of the rotating state. For uniform rotations, that is, for π‘Žπ‘›π‘› = const, the gauge transformation 𝛀, where πœ“ξ…ž(𝑑,π«ξ…ž)=exp[βˆ’(𝑖/ℏ)(π‘šπœŒ2Ξ©2/2βˆ’π‘šπœŒ2π›€πœ™/ℏ)]πœ“(𝑑,𝐫) is the distance of particles to the axis of rotation, leaves Schrodinger's equation unchanged, in accordance with its invariance under uniform rotations. In this gauge transformation, 𝜌 denotes the total momentum of inertia π‘šπœŒ2 and the first term in the phase is the kinetic energy 𝐼.

For particles in an external field, the angular momentum may have nonvanishing offdiagonal matrix elements, so nonuniform (accelerated) rotations may induce quantum transitions.

7. Conclusion

The main conclusion of the results described herein is that noninertial motion may cause quantum transitions for systems in external fields governed by Schrodinger's equation. It follows that an observer who is set in noninertial motion may record such quantum transitions. Similar transitions may be caused by changes of parameters associated with Berry's phase. The acceleration of the change of coordinates or of parameters must be fast enough in order to match the excitation spectrum of the quantum system and have such transitions.

Similar problems appear also in the field theory. For similarities with quantization in gravitational fields, we refer to [3–8].

References

  1. M. V. Berry, β€œQuantal phase factors accompanying adiabatic changes,” Proceedings of the Royal Society of London. Series A, vol. 392, no. 1802, pp. 45–57, 1984. View at Google Scholar
  2. W. G. Unruh, β€œNotes on black-hole evaporation,” Physical Review D, vol. 14, no. 4, pp. 870–892, 1976. View at Publisher Β· View at Google Scholar
  3. Y. Q. Cai and G. Papini, β€œNeutrino helicity flip from gravity-spin coupling,” Physical Review Letters, vol. 66, no. 10, pp. 1259–1262, 1991. View at Publisher Β· View at Google Scholar
  4. H. Casini and R. Montemayor, β€œChirality transitions in gravitational fields,” Physical Review D, vol. 50, no. 12, pp. 7425–7429, 1994. View at Publisher Β· View at Google Scholar Β· View at MathSciNet
  5. D. Singh, β€œNeutrino helicity and chirality transitions in Schwarzschild space-time,” Physical Review D, vol. 71, no. 10, Article ID 105003, p. 12 pages, 2005. View at Publisher Β· View at Google Scholar
  6. D. Singh and N. Mobed, β€œThe implications of noninertial motion on covariant quantum spin,” Classical and Quantum Gravity, vol. 24, no. 10, pp. 2453–2463, 2006. View at Publisher Β· View at Google Scholar Β· View at MathSciNet
  7. D. M. Greenberger and A. W. Overhauser, β€œCoherence effects in neutron diffraction and gravity experiments,” Reviews of Modern Physics, vol. 51, no. 1, pp. 43–78, 1979. View at Publisher Β· View at Google Scholar
  8. D. M. Greenberger, β€œInadequacy of the usual Galilean transformation in quantum mechanics,” Physical Review Letters, vol. 87, no. 10, Article ID 100405, p. 4 pages, 2001. View at Publisher Β· View at Google Scholar Β· View at MathSciNet