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1.
S. Kitajima F. Shibata 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):13-23
Studies on a generalized Coleman-Hepp model are done on the basis of a spin coherent state representation and a transformation
property of the model Hamiltonian. Namely, transforming the original model Hamiltonian into a simpler form, we can determine
time evolution of the whole system by successive applications of rotation operators in a spinor space. Dynamics of detector
spins as well as that of an incident particle are fully discussed. Explicit numerical evaluations are also performed. Relevance
of our solution to a generalized Cini model is also briefly mentioned.
Received 24 August 1999 相似文献
2.
J. des Cloizeaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):439-443
Dirac equation is reformulated in terms of real local observables, which are mean values of the wave function . The quadrivector current is shown to be a function of the potential vector and of other local observables. The equations
describe the evolution of a four dimensional system T, X, Y, Z, and of two scalars, in the coordinate system ct, x, y, z. The current is proportional to the T vector. The Z vector is associated with the spin of the electron. Energy and gauge transformations correspond to rotations in the plane
(X, Y). In the presence of a static field, the (real) solutions of the equations appear as eigenfunctions associated with energy
eigenvalues.
Received 7 September 1998 相似文献
3.
C.P. Sun D.L. Zhou S.X. Yu X.F. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(1):145-155
Based on the Born-Oppenhemer approximation, the concept of adiabatic quantum entanglement is introduced to account for quantum
decoherence of a quantum system due to its interaction with a large system of one or a few degrees of freedom. In the adiabatic
limit, it is shown that the wave function of the total system formed by the quantum system plus the large system can be factorized
as an entangled state with correlation between adiabatic quantum states and quasi-classical motion configurations of the large
system. In association with a novel viewpoint about quantum measurement, which has been directly verified by most recent experiments
[e.g., S. Durr et al., Nature 33, 359 (1998)], it is shown that the adiabatic entanglement is indeed responsible for the quantum decoherence and thus can
be regarded as a “clean” quantum measurement when the large system behaves as a classical object. By taking the large system
respectively to be a macroscopically distinguishable spatial variable, a high spin system and a harmonic oscillator with a
coherent initial state, three illustrations are presented with their explicit solutions in this paper.
Received 26 February 2000 and Received in final form 14 July 2000 相似文献
4.
Jia-Lin Zhu Rong Lü Su-Peng Kou Hui Hu Bing-Lin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):507-513
The quantum interference effects induced by the Wess-Zumino term, or Berry phase are studied theoretically in resonant quantum
coherence of the magnetization vector between degenerate states in nanometer-scale single-domain ferromagnets in the absence
of an external magnetic field. We consider the magnetocrystalline anisotropy with trigonal, tetragonal and hexagonal crystal
symmetry, respectively. By applying the periodic instanton method in the spin-coherent-state path integral, we evaluate the
low-lying tunnel splittings between degenerate excited states of neighboring wells. And the low-lying energy level spectrum
of mth excited state are obtained with the help of the Bloch theorem in one-dimensional periodic potential. The energy level spectrum
and the thermodynamic properties of magnetic tunneling states are found to depend significantly on the total spins of ferromagnets
at sufficiently low temperatures. Possible relevance to experiments is also discussed.
Received 15 December 1999 相似文献
5.
J. Weis O. Weis 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):135-146
This paper is concerned with the transmission time of an incident Gaussian wave packet through a symmetric rectangular barrier.
Following Hartman (J. Appl. Phys. 33, 3427 (1962)), the transmission time is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness
and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission
velocity which appears under certain conditions as a supervelocity, i.e. becomes larger than the corresponding propagation velocity in free space which is the group velocity for electrons or the
velocity of light for photons, respectively. By analysing the propagation of a broadband wave packet (which leads in free
space to an extremely concentrated wave packet at a certain time) we obtain the pulse response function of the barrier and
show that the insertion of the barrier is physically unable to produce a supervelocity. Therefore, the peak of an incident
Gaussian wave packet and the peak of the transmitted wave packet are in no causal relationship. The shape of the transmitted
wave packet is produced from the incident wave by convolution with the pulse response of the barrier. This yields a distortion
of the shape of the wave packet which includes also the observed negative time shift of the peak. We demonstrate further that
the phenomenon of Hartman's supervelocities is not restricted to barriers with their exponentially decaying fields but occurs
for instance also in transmission lines with an inserted LCR circuit.
Received 7 January 1999 and Received in final form 22 April 1999 相似文献
6.
C. Tsallis D. Prato C. Anteneodo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):605-611
We consider a statistical mixture based on that of two identical harmonic oscillators which is characterized by four parameters,
namely, the concentrations (x and y) of diagonal and nondiagonal bipartite states, and their associated thermal-like noises (T/α and T, respectively). The fully random mixture of two spins 1/2 as well as the Einstein-Podolsky-Rosen (EPR) state are recovered
as particular instances. By using the conditional nonextensive entropy as introduced by Abe and Rajagopal, we calculate a
bound for the separable-entangled frontier. Although this procedure is known to provide a necessary but in general not sufficient condition for separability, it does recover, in the particular case x = T = 0 ( ∀α), the 1/3 exact result known as Peres' criterion. The x = 0 frontier remarkably resembles to the critical line associated with standard diluted ferromagnetism where the entangled
region corresponds to the ordered one and the separable region to the paramagnetic one. The entangled region generically shrinks
for increasing T or increasing α.
Received 18 April 2002 / Received in final form 11 July 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: celia@cbpf.br 相似文献
7.
M. Konôpka V. Bužek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(2):285-293
We propose a method for entangling a system of two-level atoms in photonic crystals. The atoms are assumed to move in void
regions of a photonic crystal. The interaction between the atoms is mediated either via a defect mode or via a resonant dipole-dipole interaction. We show that these interactions can produce pure entangled atomic states. We analyze the problem with parameters typical
for currently existing photonic crystals and Rydberg atoms and we show that the atoms can emerge from photonic crystals in
entangled states. Depending on the linear dimensions of the crystal we estimate that a pair of atoms entangled in a photonic
crystal can be separated by tens of centimeters.
Receive 11 June 1999 and Received in final form 4 October 1999 相似文献
8.
J.S. Briggs J.M. Rost 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):311-318
It is shown that the time-dependent equations (Schr?dinger and Dirac) for a quantum system can be derived from the time-independent
equation for the larger object of the system interacting with its environment, in the limit that the dynamical variables of
the environment can be treated semiclassically. The time which describes the quantum evolution is then provided parametrically
by the classical evolution of the environment variables. The method used is a generalization of that known for a long time
in the field of ion-atom collisions, where it appears as a transition from the full quantum mechanical perturbed stationary states to the impact parameter method in which the projectile ion beam is treated classically.
Received 25 October 1999 相似文献
9.
S. Wallentowitz R.L. de Matos Filho S.-C. Gou W. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(3):397-405
We present a method for the direct measurement of the Wigner-function matrix for complex vibronic states of a trapped atom,
that is suited to analyse the entanglement between two motional degrees of freedom and the internal electronic dynamics. It
is a generalisation of the method for the determination of vibronic quantum states [S. Wallentowitz, R.L. de Matos Filho,
W. Vogel, Phys. Rev. A 56, 1205 (1997)] in conjunction with the scheme for the direct observation of the Wigner function of a single motional degree
of freedom [L.G. Lutterbach, L. Davidovich, Phys. Rev. Lett. 78, 2547 (1997)]. The major advantage of the present method is that it reduces the experimental efforts substantially. On the
other hand, it is demonstrated that the nonlinear vibronic coupling necessary for this method turns out to be its main limitation.
Received: 5 August 1998 相似文献
10.
Rong Lü Hui Hu Jia-Lin Zhu Xiao-Bing Wang Lee Chang Bing-Lin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):349-361
Resonant quantum tunneling of the Néel vector between nonequivalent magnetic wells is investigated theoretically for a nanometer-scale
single-domain antiferromagnet with biaxial crystal symmetry in the presence of an external magnetic field applied along the
easy anisotropy axis, based on the two-sublattice model. Both the Wentzel-Kramers-Brillouin exponent and the preexponential
factors are evaluated in the instanton contribution to the tunneling rate for finite and zero magnetic fields by applying
the instanton technique in the spin-coherent-state path-integral representation, respectively. The quantum interference or
spin-parity effects induced by the topological phase term in the Euclidean action are discussed in the rate of quantum tunneling
of the Néel vector. In the absence of an external applied magnetic field, the effect of destructive phase interference or
topological quenching on resonant quantum tunneling of the Néel vector is evident for the half-integer excess spin antiferromagnetic
nanoparticle. In the weak field limit, the tunneling rates are found to oscillate with the external applied magnetic field
for both integer and half-integer excess spins. We discuss the experimental condition on the applied magnetic field which
may allow one to observe the topological quenching effect for nanometer-scale single-domain antiferromagnets with half-integer
excess spins. Tunneling behavior in resonant quantum tunneling of the magnetization vector between nonequivalent magnetic
wells is also studied for a nanometer-scale single-domain ferromagnet by applying the similar technique, but in the large
noncompensation limit.
Received 4 June 1999 相似文献
11.
Reliable teleportation in trapped ions 总被引:8,自引:0,他引:8
E. Solano C.L. Cesar R.L. de Matos Filho N. Zagury 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(1):121-128
We study a method for the implementation of a reliable teleportation protocol (theoretically, 100% of success) of internal
states in trapped ions. The generation of the quantum channel (any of four Bell states) may be done respecting technical limitations
on individual addressing and without claiming the Lamb-Dicke regime. An adequate Bell analyzer, that transforms unitarily
the Bell basis into a completely disentangled one, is considered. Probable sources of error and fidelity estimations of the
teleportation process are studied. Finally, we discuss experimental issues, proposing a scenario in which the present scheme
could be implemented.
Received 1st June 2000 and Received in final form 17 August 2000 相似文献
12.
13.
A. C. de la Torre A. Daleo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):165-168
Two types of particles, A and B with their corresponding antiparticles, are defined in a onedimensional cyclic lattice with an odd number of sites. In each
step of time evolution, each particle acts as a source for the polarization field of the other type of particle with nonlocal
action but with an effect decreasing with the distance: . It is shown that the combined distribution of these particles obeys the time evolution of a free particle as given by quantum
mechanics. 相似文献
14.
J.M. Hansteen L. Kocbach 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):323-326
A new type of collision experiments is discussed, where observations of two successive collisions of the same pair of particles would be possible. When such technology is available, a surprising restoring of entanglement, normally considered
broken in usual collision experiments, could be observed. As an illustration the collision partners He+ and He++ in a collision regime where the resonant charge transfer is dominating are considered. In the analysis it is shown that in
such experiments, two spatially widely separated ion paths, corresponding in fact to two different charge states, would contribute
coherently to the final amplitudes, describing which of the ions emerges as singly charged, i.e. which carries the single electron involved. The double collision experiments are not trivial, since their overall cross-sections
are extremely small. Development of relevant experimental techniques will decide if the proposed phenomena remain in the field
of gedanken experiments or enter the world of real experimental physics.
Received 2 December 1999 and Received in final form 12 May 2000 相似文献
15.
Paulina Marian Tudor A. Marian 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):257-265
We analyze the transient nonclassical behaviour of a single-mode field whose interaction with an environment is governed by
the quantum optical master equation. Our analytic method makes use of the generalized characteristic function of the field
state. First, we find a time at which all squeezing effects disappear by decoherence regardless of the initial state of the
mode. In the case of an input even coherent state, an unusual modification of higher-order squeezing at low values of thermal
mean occupancy transferred to the field is found and discussed. For the same initial state, we also perform a comprehensive
analysis of the mixing process during the interaction with the reservoir. We prove that a maximum in the evolution of the
2-entropy of the attenuated mode exists on condition that its initial mean photon number exceeds the mean occupancy of the
reservoir. This transient mixing enhancement can be considered as a quantum effect of the initial state on the mode damping.
Received 22 April 1999 and Received in final form 2 November 1999 相似文献
16.
A. Luis L.L. Sánchez-Soto 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(2):195-200
We reconsider the problem of the sum and difference of two angle variables in quantum mechanics. The spectra of the sum and
difference operators have widths of , but angles differing by are indistinguishable. This means that the angle sum and difference probability distributions must be cast into a range. We obtain probability distributions for the angle sum and difference and relate this problem to the representation
of nonbijective canonical transformations.
Received: 6 December 1997 / Revised: 15 April 1998 / Accepted: 7 May
1998 相似文献
17.
J. Gemmer G. Mahler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):249-257
For a closed bi-partite quantum system partitioned into system proper and environment we interpret the microcanonical and
the canonical condition as constraints for the interaction between those two subsystems. In both cases the possible pure-state
trajectories are confined to certain regions in Hilbert space. We show that in a properly defined thermodynamical limit almost
all states within those accessible regions represent states of some maximum local entropy. For the microcanonical condition
this dominant state still depends on the initial state; for the canonical condition it coincides with that defined by Jaynes'
principle. It is these states which thermodynamical systems should generically evolve into.
Received 13 June 2002 / Received in final form 14 November 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: jochen@theol.physik.uni-stuttgart.de 相似文献
18.
A. Teğmen T. Altanhan B. S. Kandemir 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):397-402
We calculate the Wigner distribution function for the
Calogero-Sutherland system which consists of harmonic and
inverse-square interactions. The Wigner distribution function is
separated out into two parts corresponding to the relative and
center-of-mass motions. A general expression for the relative
Wigner function is obtained in terms of the Laguerre polynomials
by introducing a new identity between Hermite and Laguerre
polynomials. 相似文献
19.
P. Horak H. Ritsch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):279-287
We propose a method to create macroscopic superpositions, so-called Schr?dinger cat states, of different motional states of
an ideal Bose-Einstein condensate. The scheme is based on the scattering of a freely expanding condensate by the light field
of a high-finesse optical cavity in a quantum superposition state of different photon numbers. The atom-photon interaction
creates an entangled state of the motional state of the condensate and the photon number, which can be converted into a pure
atomic Schr?dinger cat state by operations only acting on the cavity field. We discuss in detail the fully quantised theory
and propose an experimental procedure to implement the scheme using short coherent light pulses.
Received 26 June 2000 and Received in final form 2nd October 2000 相似文献
20.
J. Yi G. Cuniberti M. Porto 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):221-225
We examine the anomalous behavior of the transmittance through a one-dimensional ring having two branches of different lengths,
as determined by the lead positions. Jumps in the transmittance phase are occurring in correspondence to both (a) zeros in
the transmission at the eigenstates of the isolated ring and (b) destructive interference events. It is also found that when
the ratio of the branch lengths is given by p/q satisfying p + q = 0(mod 4), the two characteristic zeros merge into a single point and the transmittance phase becomes identical to the so-called
Friedel phase.
Received 7 June 2002 / Received in final form 11 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: juyeon.yi@physik.uni-regensburg.de 相似文献