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2.
J.-B. Liu J.-H. Li X.-Y. Lü A. Zheng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):601-606
In this paper, we investigate the geometric phase of a composite system which is composed of two spin-
particles driven by a
time-varying magnetic field. Firstly, we consider the special case that only one subsystem driven by time-varying magnetic
field. Using the quantum jump
approach, we calculate the geometric phase associated with the adiabatic evolution of the system subjected to decoherence.
The results show that the lowest
order corrections to the phase in the no-jump trajectory is only quadratic in decoherence coefficient. Then, both subsystem
driven by time-varying magnetic
field is considered, we show that the geometric phase is related to the exchange-interaction coefficient and polar angle of
the magnetic field. 相似文献
3.
A. S. Sanz F. Borondo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):319-326
A complete theoretical treatment in many problems relevant to
physics, chemistry, and biology requires considering the action
of the environment over the system of interest.
Usually the environment involves a relatively large number of degrees
of freedom, this making the problem numerically intractable from a
purely quantum-mechanical point of view.
To overcome this drawback, a new class of quantum trajectories is
proposed.
These trajectories, based on the same grounds as Bohmian ones, are
solely associated to the system reduced density matrix, since the
evolution of the environment degrees of freedom is not considered
explicitly.
Within this approach, environment effects come into play through a
time-dependent damping factor that appears in the system equations
of motion.
Apart from their evident computational advantage, this type of
trajectories also results very insightful to understand the system
decoherence.
In particular, here we show the usefulness of these trajectories
analyzing decoherence effects in interference phenomena, taking as
a working model the well-known double-slit experiment. 相似文献
4.
Z. Haba H. Kleinert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):553-560
We set up a forward - backward path integral for a point particle in a bath of photons to derive a master equation for the
density matrix which describes electromagnetic dissipation and decoherence. We also derive the associated Langevin equation.
As an application, we recalculate the Wigner-Weisskopf formula for the natural line width of an atomic state at zero temperature
and find, in addition, the temperature broadening caused by the decoherence term. Our master equation also yields the correct
Lamb shift of atomic levels. The two equations may have applications to dilute interstellar gases or to few-particle systems
in cavities.
Received 29 November 2000 and Received in final form 11 February 2001 相似文献
5.
O. V. Zhirov D. L. Shepelyansky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):405-408
Using the methods of quantum trajectories
we study effects of dissipative decoherence on the accuracy
of the Grover quantum search algorithm.
The dependence on the number of qubits and
dissipation rate are determined and tested numerically
with up to 16 qubits. As a result,
our numerical and analytical studies give
the universal law for decay of fidelity and
probability of searched state which are induced by dissipative
decoherence effects. This law is in agreement with
the results obtained previously for quantum chaos algorithms. 相似文献
6.
R.K. Varma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):211-218
It has been shown earlier [3,6] that matter waves which are known to lie typically in the range of a few angstrom, can also
manifest in the macrodomain with a wave length of a few centimeters, for electrons propagating along a magnetic field. This
followed from the predictions of a probability amplitude theory by the author [1,2] in the classical macrodomain of the dynamics
of charged particles in a magnetic field. It is shown in this paper that this case constitutes only a special case of a generic
situation whereby composite systems such as atoms and molecules in their highly excited internal states, can exhibit matter
wave manifestation in macro and mesodomains, in one-dimensional scattering. The wave length of these waves is determined,
not by the mass of the particle as in the case of the de Broglie wave, but by the frequency ω, of the classical orbital motion
of the internal state in the correspondence limit, and is given by a nonquantal expression, λ = 2πv/ω, v being the velocity of the particle. For the electrons in a magnetic field the frequency corresponds to the gyrofrequency,
Ω and the nonquantal wave length is given by λ = 2πv
|| /Ω; v
|| being the velocity of electrons along the magnetic field.
Received 29 September 2001 / Received in final form 23 May 2002 Published online 19 July 2002 相似文献
7.
D. Braun 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(1):103-108
The interaction of two–level atoms with a common heat bath leads to an effective interaction between the atoms, such that
with time the internal degrees of the atoms become correlated or even entangled. If part of the atoms remain unobserved this
creates
additional indirect decoherence for the selected atoms, on top of the direct decoherence due to the interaction with the heat
bath. I show that indirect decoherence can drastically increase and
even dominate the decoherence for sufficiently large times. I investigate indirect decoherence through thermal black body
radiation quantitatively for atoms trapped at regular positions in an optical lattice as well as for atoms at random positions
in a cold gas, and show how indirect
decoherence can be controlled or even suppressed through experimentally accessible parameters. 相似文献
8.
J. Botero M.A. Cirone J.P. Dahl F. Straub W.P. Schleich 《Applied physics. B, Lasers and optics》2003,76(2):129-133
We express the commutation relation between the operators of the momentum and the radial unit vectors in D dimensions in differential
and integral form. We connect this commutator with the quantum fictitious potential emerging in the radial Schr?dinger equation
of an s-wave.
Received: 6 August 2002 / Revised version: 30 October 2002 / Published online: 26 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-731/502-3086, E-mail: markus.cirone@physik.uni-ulm.de 相似文献
9.
J. Eckel S. Weiss M. Thorwart 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):91-98
We investigate the phonon-induced decoherence and dissipation in a
donor-based charge quantum bit realized by the orbital states of an
electron shared by two dopant ions which are implanted in a
silicon host crystal. The dopant ions are taken from the group-V
elements Bi, As, P, Sb. The excess electron is
coupled to deformation potential acoustic phonons which dominate in
the Si host. The particular geometry tailors a non-monotonous frequency
distribution of the phonon modes. We determine the exact qubit dynamics
under the influence of the phonons by employing
the numerically exact
quasi-adiabatic propagator path integral scheme thereby taking
into account all bath-induced correlations. In particular, we
have improved the scheme by completely eliminating the Trotter
discretization error by a Hirsch-Fye extrapolation. By comparing
the exact results to those of a Born-Markov
approximation we find that the latter yields appropriate estimates for
the decoherence and relaxation rates. However, noticeable quantitative
corrections due to non-Markovian contributions appear. 相似文献
10.
L. Jacak P. Machnikowski J. Krasnyj P. Zoller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):319-331
Carrier-phonon interaction in semiconductor quantum dots leads to three classes of phenomena: coherent effects (spectrum reconstruction)
due to the nearly-dispersionless LO phonons, incoherent effects (transitions) induced by acoustical phonons and dressing phenomena,
related to non-adiabatic, sub-picosecond excitation. Polaron spectra, relaxation times and dressing-related decoherence rates
are calculated, in accordance with experiment.
Received 30 August 2002 / Received in final form 25 November 2002 Published online 28 January 2003 相似文献
11.
We study the effect of photon scattering from a path of a four-beam atomic interference setup, which is based on a cesium
atomic beam and two subsequent optical Ramsey pulses projecting the atoms onto a multilevel dark state. While in two-beam
interference, any attempt to keep track of an interfering path reduces the fringe contrast, we demonstrate that photon scattering
in a multiple-path arrangement cannot only lead to a decrease, but - under certain conditions - also to an increase of the
interference contrast. The results are confirmed by a density-matrix calculation. We are aware that in all cases the “which-path”
information carried away by the scattered photons leads to a loss of information that is contained in the atomic quantum state.
An approach to quantify this “which-path” information using observed fringe signals is presented; it allows for an appropriate
measure of quantum decoherence in multiple-path interference.
Received: 27 July 2000 / Published online: 6 December 2000 相似文献
12.
M.-M. He G. Chen J.-Q. Liang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):581-583
In this paper we investigate the Berry phase in Tavis-Cummings model in the
rotating wave approximation. The dipole-dipole interaction between the atoms
is considered. The eigenfunctions of the system are obtained and thus the
Berry phase is evaluated explicitly in terms of the introduction of the
phase shift. It is shown that the Berry phase can be easily controlled by
the atom-cavity coupling strength, the cavity frequency detuning, which can
be important in applications in geometric quantum computing. 相似文献
13.
Yu.L. Sokolov V.P. Yakovlev V.G. Pal'chikov Yu.A. Pchelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):27-36
The properties of two-dimensional magnetic traps for laser-cooled atoms are analysed using complex functions. The two components
of the magnetic field from a series of parallel, infinitely long, current-carrying wires are represented by a single complex
number. The regions of the field where paramagnetic atoms can be trapped occur where the magnetic field is zero. The locations
of the zeroes of the field are obtained as the solution to a polynomial and the multiplicity m of the solution determines both the 2(m + 1)-pole nature of the trap and the field gradient through the centre. The zeroes of the field can be merged or split by
varying the locations of the currents, their strengths or by applying a uniform magnetic field. The theory is applied to magnetic
traps created from long thin wires or permanent magnets on a substrate. The properties of a number of magnetic trap configurations
used for atom guides are discussed.
Received 28 February 2001 and Received in final form 6 July 2001 相似文献
14.
S. Franke-Arnold S.M. Barnett G. Huyet C. Sailliot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):373-383
We analyse the coherence properties of two particles trapped in a one-dimensional harmonic potential. This simple model allows
us to derive analytic expressions for the first and second order coherence functions. We investigate their properties depending
on the particle nature and the temperature of the quantum gas. We find that at zero temperature non-interacting bosons and
fermions show very different correlations, while they coincide for higher temperatures. We observe atom bunching for bosons
and atom anti-bunching for fermions. When the effect of s-wave scattering between bosons is taken into account, we find that the range of coherence is enhanced or reduced for repulsive
or attractive potentials, respectively. Strongly repelling bosons become in some way more “fermion-like" and show anti-bunching.
Their first order coherence function, however, differs from that for fermions.
Received 19 September 2002 Published online 4 February 2003 相似文献
15.
R. Srikanth S. Banerjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(2):217-227
We develop an information theoretic interpretation of the number-phase complementarity in atomic systems, where phase is treated
as a continuous positive operator valued measure (POVM). The relevant uncertainty principle is obtained as an upper bound
on a sum of knowledge of these two observables for the case of two-level systems. A tighter bound characterizing the uncertainty
relation is obtained numerically in terms of a weighted knowledge sum involving these variables. We point out that complementarity
in these systems departs from mutual unbiasededness in two significant ways: first, the maximum knowledge of a POVM variable
is less than log (dimension) bits; second, surprisingly, for higher dimensional systems, the unbiasedness may not be mutual
but unidirectional in that phase remains unbiased with respect to number states, but not vice versa. Finally, we study the
effect of non-dissipative and dissipative noise on these complementary variables for a single-qubit system. 相似文献
16.
N.P. Proukakis P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):355-370
We present a consistent second order perturbation theory for the lowest-lying condensed modes of very small, weakly-interacting
Bose-Einstein condensates in terms of bare particle eigenstates in a harmonic trap. After presenting our general approach,
we focus on explicit expressions for a simple three-level system, mainly in order to discuss the analogy of a single condensate
occupying two modes of a trap with the semi-classical theory for two-mode photon lasers. A subsequent renormalization of the
single-particle energies to include the dressing imposed by mean fields demonstrates clearly the consistency of our treatment
with other kinetic approaches.
Received 14 December 2001 相似文献
17.
A. Vaglica G. Vetri 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(1):9-19
We analyze the time evolution of an initial spatial
coherence for a two level atom whose internal degrees of freedom
interact with a single mode of a cavity field. When the
qubit-field subsystem is taken as an environment, the
translational dynamics experiences a decoherence process which may
be encoded in a decoherence factor D. We find that the field
statistics affects D through the alternative paths the
system-environment may follow along their entanglement, while
eventual field phase properties give rise to an imaginary part of
D which is related to the atomic translation. From the
decoherence perspective, we analyze the relation between the
atomic momentum and the imaginary part of the atomic spatial
density matrix, and some considerations on its asymptotic behavior
are brought into question at the conclusion of the paper. 相似文献
18.
E.B. Karlsson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):393-400
The coherence in quantum superposition states of protons (and chemically similar particles, the positive muons) has been studied
in some condensed matter environments. It is shown that if the proton systems and the experimental techniques used to study
them are carefully selected, it is possible to observe quantum delocalization states of single particles and to understand
the mechanisms for their loss of coherence. Quantum correlated two- and multiparticle states of protons lose coherence very
fast when coupled to condensed matter environments, but new sub-femtosecond techniques have made them accessible to experimental
studies. The degree of decoherence can be measured as function of time and the decoherence mechanisms can, at least in certain
cases, be identified. Although less clean than in corresponding studies of quantum optical systems, these studies can be seen
as a first step towards understanding the conditions for preservation of quantum correlation and entanglement in massive systems.
Some consequences and some suggestions for future work are discussed.
Received 28 August 2002 Published online 7 January 2003 相似文献
19.
S. Banerjee R. Srikanth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):335-344
We study the geometric phase of an open two-level quantum
system under the influence of a squeezed, thermal environment for both
non-dissipative as well as dissipative system-environment
interactions. In the non-dissipative case, squeezing is found to have
a similar influence as temperature, of suppressing geometric phase,
while in the dissipative case, squeezing tends to counteract the
suppressive influence of temperature in certain regimes. Thus, an
interesting feature that emerges from our work is the contrast in the
interplay between squeezing and thermal effects in non-dissipative and
dissipative interactions. This can be useful for the practical
implementation of geometric quantum information processing. By
interpreting the open quantum effects as noisy channels, we make the
connection between geometric phase and quantum noise processes
familiar from quantum information theory. 相似文献
20.
A. R.R. Carvalho F. Mintert S. Palzer A. Buchleitner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):425-432
We investigate the time evolution of entanglement for bipartite systems of
arbitrary dimensions under the influence of decoherence. For qubits, we
determine the precise entanglement decay rates under different
system-environment couplings, including finite temperature effects. For qudits, we show how
to obtain upper bounds for the decay rates and also present exact solutions
for various classes of states. 相似文献