7,441 research outputs found
Influence functional approach to decoherence during Inflation
We show how the quantum to classical transition of the cosmological
fluctuations produced during inflation can be described by means of the
influence functional and the master equation. We split the inflaton field into
the system-field (long-wavelength modes), and the environment, represented by
its own short-wavelength modes. We compute the decoherence times for the
system-field modes and compare them with the other time scales of the model.Comment: 6 pages, no figures. Contributed talk to the Second International
Workshop DICE2004, Piombino, Ital
Decoherence in a Two Slit Diffraction Experiment with Massive Particles
Matter-wave interferometry has been largely studied in the last few years.
Usually, the main problem in the analysis of the diffraction experiments is to
establish the causes for the loss of coherence observed in the interference
pattern. In this work, we use different type of environmental couplings to
model a two slit diffraction experiment with massive particles. For each model,
we study the effects of decoherence on the interference pattern and define a
visibility function that measures the loss of contrast of the interference
fringes on a distant screen. Finally, we apply our results to the experimental
reported data on massive particles .Comment: 6 pages, 3 figure
Noise-induced energy excitation by a general environment
We analyze the effects that general environments, namely ohmic and non-ohmic,
at zero and high temperature induce over a quantum Brownian particle. We state
that the evolution of the system can be summarized in terms of two main
environmental induced physical phenomena: decoherence and energy activation. In
this article we show that the latter is a post-decoherence phenomenon. As the
energy is an observable, the excitation process is a direct indication of the
system-environment entanglement particularly useful at zero temperature.Comment: 14 pages; 7 figures. Version to appear in Phys Lett.
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
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.
Onset of classical behaviour after a phase transition
We analyze the onset of classical behaviour in a scalar field after a
continuous phase transition, in which the system-field, the long wavelength
order parameter of the model, interacts with an environment of its own
short-wavelength modes. We compute the decoherence time for the system-field
modes from the master equation and compare it with the other time scales of the
model. Within our approximations the decoherence time is in general the
smallest dynamical time scale. Demanding diagonalisation of the decoherence
functional produces identical results. The inclusion of other environmental
fields makes diagonalisation occur even earlier.Comment: Seven pages, no figures. Contributed talk to the Second International
Workshop DICE2004, Piombino, Italy. To be published in the Brazilian Journal
of Physic
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