6,283 research outputs found
Geometric phase accumulated in a driven quantum system coupled to an structured environment
We study the role of driving in a two-level system evolving under the
presence of a structured environment. We find that adding a periodical
modulation to the two-level system can greatly enhance the survival of the
geometric phase for many time periods. We show that this effect is mainly
important for a markovian regimen but can still be found when the environment
exhibits non-markovian behavior as time revivals. This knowledge can aid the
search for physical set-ups that best retain quantum properties under
dissipative dynamics.Comment: To appear in Phys. Rev. A. arXiv admin note: text overlap with
arXiv:1001.3564 by other author
Correction to the geometric phase by structured environments: the onset of non-Markovian effects
We study the geometric phase of a two-level system under the presence of a
structured environment, particularly analysing its correction with the ohmicity
parameter and the onset of non-Markovianity. We firstly examine the system
coupled to a set of harmonic oscillators and studied the decoherence factor as
function of the environment's ohmicity parameter. Secondly, we propose the
two-level system coupled to a non-equilibrium environment, and show that these
environments display non-Markovian effects for all values of the ohmicity
parameter. The geometric phase of the two-level system is therefore computed
under the presence of both types of environment. The correction to the unitary
geometric phase is analysed in both, Markovian and non-Markovian regimes. Under
Markovian environments, the correction induced on the system's phase is mainly
ruled by the coupling constant between the system and the environment, while in
the non-Markovian regime, memory effects seem to trigger a significant
correction to the unitary geometric phase. The result is significant to the
quantum information processing based on the geometric phase in quantum open
systemsComment: 7 figures. Accepted for publication in Phys. Rev. A. arXiv admin
note: text overlap with arXiv:1303.493
Decoherence in composite quantum open systems: the effectiveness of unstable degrees of freedom
The effect induced by an environment on a composite quantum system is
studied. The model considers the composite system as comprised by a subsystem A
coupled to a subsystem B which is also coupled to an external environment. We
study all possible four combinations of subsystems A and B made up with a
harmonic oscillator and an upside down oscillator. We analyzed the decoherence
suffered by subsystem A due to an effective environment composed by subsystem B
and the external reservoir. In all the cases we found that subsystem A
decoheres even though it interacts with the environment only through its sole
coupling to B. However, the effectiveness of the diffusion depends on the
unstable nature of subsystem A and B. Therefore, the role of this degree of
freedom in the effective environment is analyzed in detailComment: 20 pages, 4 figures. Version to appear in Int. J. Mod. Phys.
Decoherence of a solid-state qubit by different noise correlation spectra
The interaction between solid-state qubits and their environmental degrees of
freedom produces non-unitary effects like decoherence and dissipation.
Uncontrolled decoherence is one of the main obstacles that must be overcome in
quantum information processing. We study the dynamically decay of coherences in
a solid-state qubit by means of the use of a master equation. We analyse the
effects induced by thermal Ohmic environments and low-frequency 1/f noise. We
focus on the effect of longitudinal and transversal noise on the
superconducting qubit's dynamics. Our results can be used to design
experimental future setups when manipulating superconducting qubits.Comment: 14 pages, 9 figures. Version to appear in Physics Letters A. arXiv
admin note: text overlap with arXiv:0809.4716 by other author
Macroscopic tunneling, decoherence and noise-induced activation
We study the effects of the environment at zero temperature on tunneling in
an open system described by a static double-well potential. We show that the
evolution of the system in an initial Schrodinger cat state, can be summarized
in terms of three main physical phenomena, namely decoherence, quantum
tunneling and noise-induced activation. Using large-scale numerical
simulations, we obtain a detailed picture of the main stages of the evolution
and of the relevant dynamical processesComment: Contribution to the Proceedings of DICE'0
Spin bath interactions effects on the geometric phase
We calculate the geometric phase of a spin-1/2 particle coupled to an
external environment comprising N spin-1/2 particle in the framework of open
quantum systems. We analyze the decoherence factor and the deviation of the
geometric phase under a nonunitary evolution from the one gained under an
unitary one. We show the dependence upon the system's and bath's parameter and
analyze the range of validity of the perturbative approximation. Finally, we
discuss the implications of our results.Comment: 8 pages, 5 figures. Version to appear in Phys. Lett.
Using boundary methods to compute the Casimir energy
We discuss new approaches to compute numerically the Casimir interaction
energy for waveguides of arbitrary section, based on the boundary methods
traditionally used to compute eigenvalues of the 2D Helmholtz equation. These
methods are combined with the Cauchy's theorem in order to perform the sum over
modes. As an illustration, we describe a point-matching technique to compute
the vacuum energy for waveguides containing media with different
permittivities. We present explicit numerical evaluations for perfect
conducting surfaces in the case of concentric corrugated cylinders and a
circular cylinder inside an elliptic one.Comment: To be published in the Proceedings of QFEXT09, Norman, OK
Visibility Fringe Reduction Due to Noise-Induced Effects: Microscopic Approach to Interference Experiments
Decoherence is the main process behind the quantum to classical transition.
It is a purely quantum mechanical effect by which the system looses its ability
to exhibit coherent behavior. The recent experimental observation of
diffraction and interference patterns for large molecules raises some
interesting questions. In this context, we identify possible agents of
decoherence to take into account when modeling these experiments and study
theirs visible (or not) effects on the interference pattern. Thereby, we
present an analysis of matter wave interferometry in the presence of a dynamic
quantum environment and study how much the visibility fringe is reduced and in
which timescale the decoherence effects destroy the interference of massive
objects. Finally, we apply our results to the experimental data reported on
fullerenes and cold neutrons.Comment: 14 pages, 5 figures. Version to appear in Mod. Phys.
Geometric phases in open systems: an exact model to study how they are corrected by decoherence
We calculate the geometric phase for an open system (spin-boson model) which
interacts with an environment (ohmic or nonohmic) at arbitrary temperature.
However there have been many assumptions about the time scale at which the
geometric phase can be measured, there has been no reported observation yet for
mixed states under nonunitary evolution. We study not only how they are
corrected by the presence of the different type of environments but also
estimate the corresponding times at which decoherence becomes effective. These
estimations should be taken into account when planning experimental setups to
study the geometric phase in the nonunitary regime, particularly important for
the application of fault-tolerant quantum computation.Comment: Revtex 4, 5 pages, one eps figure. Version Publishe
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