79 research outputs found
Universal Dynamical Control of Local Decoherence for Multipartite and Multilevel Systems
A unified theory is given of dynamically modified decay and decoherence of
field-driven multilevel multipartite entangled states that are weakly coupled
to zero-temperature baths or undergo random phase fluctuations. The theory
allows for arbitrary local differences in their coupling to the environment.
Due to such differences, the optimal driving-field modulation to ensure maximal
fidelity is found to substantially differ from conventional ``Bang-Bang'' or
-phase flips of the single-qubit evolution.Comment: 22 pages, 6 figure
Comment on "Evolution of a Quasi-Stationary State"
Approximately forty years ago it was realized that the time development of
decaying systems might not be precisely exponential. Rolf Winter (Phys. Rev.
{\bf 123}, 1503 (1961)) analyzed the simplest nontrivial system - a particle
tunneling out of a well formed by a wall and a delta-function. He calculated
the probability current just outside the well and found irregular oscillations
on a short time scale followed by an exponential decrease followed by more
oscillations and finally by a decrease as a power of the time. We have
reanalyzed this system, concentrating on the survival probability of the
particle in the well rather than the probability current, and find a different
short time behavior.Comment: 8 pages, 6 figures, RevTex
Decay process accelerated by tunneling in its very early stage
We examine a fast decay process that arises in the transition period between
the Gaussian and exponential decay processes in quantum decay systems. It is
usually expected that the decay is decelerated by a confinement potential
barrier. However, we find a case where the decay in the transition period is
accelerated by tunneling through a confinement potential barrier. We show that
the acceleration gives rise to an appreciable effect on the time evolution of
the nonescape probability of the decay system.Comment: 4 pages, 6 figures; accepted for publication in Phys. Rev.
Real measurements and Quantum Zeno effect
In 1977, Mishra and Sudarshan showed that an unstable particle would never be
found decayed while it was continuously observed. They called this effect the
quantum Zeno effect (or paradox). Later it was realized that the frequent
measurements could also accelerate the decay (quantum anti-Zeno effect). In
this paper we investigate the quantum Zeno effect using the definite model of
the measurement. We take into account the finite duration and the finite
accuracy of the measurement. A general equation for the jump probability during
the measurement is derived. We find that the measurements can cause inhibition
(quantum Zeno effect) or acceleration (quantum anti-Zeno effect) of the
evolution, depending on the strength of the interaction with the measuring
device and on the properties of the system. However, the evolution cannot be
fully stopped.Comment: 3 figure
Quantum Zeno and anti-Zeno effects by indirect measurement with finite errors
We study the quantum Zeno effect and the anti-Zeno effect in the case of
`indirect' measurements, where a measuring apparatus does not act directly on
an unstable system, for a realistic model with finite errors in the
measurement. A general and simple formula for the decay rate of the unstable
system under measurement is derived. In the case of a Lorentzian form factor,
we calculate the full time evolutions of the decay rate, the response of the
measuring apparatus, and the probability of errors in the measurement. It is
shown that not only the response time but also the detection efficiency plays a
crucial role. We present the prescription for observing the quantum Zeno and
anti-Zeno effects, as well as the prescriptions for avoiding or calibrating
these effects in general experiments.Comment: 4 pages, 3 figure
Effects of decoherence and errors on Bell-inequality violation
We study optimal conditions for violation of the Clauser-Horne-Shimony-Holt
form of the Bell inequality in the presence of decoherence and measurement
errors. We obtain all detector configurations providing the maximal Bell
inequality violation for a general (pure or mixed) state. We consider local
decoherence which includes energy relaxation at the zero temperature and
arbitrary dephasing. Conditions for the maximal Bell-inequality violation in
the presence of decoherence are analyzed both analytically and numerically for
the general case and for a number of important special cases. Combined effects
of measurement errors and decoherence are also discussed.Comment: 18 pages, 5 figure
Influence of the detector's temperature on the quantum Zeno effect
In this paper we study the quantum Zeno effect using the irreversible model
of the measurement. The detector is modeled as a harmonic oscillator
interacting with the environment. The oscillator is subjected to the force,
proportional to the energy of the measured system. We use the Lindblad-type
master equation to model the interaction with the environment. The influence of
the detector's temperature on the quantum Zeno effect is obtained. It is shown
that the quantum Zeno effect becomes stronger (the jump probability decreases)
when the detector's temperature increases
Scalaron the mighty: producing dark matter and baryon asymmetry at reheating
In R^2-inflation scalaron slow roll is responsible for the inflationary
stage, while its oscillations reheat the Universe. We find that the same
scalaron decays induced by gravity can also provide the dark matter production
and leptogenesis. With R^2-term and three Majorana fermions added to the
Standard Model, we arrive at the phenomenologically complete theory capable of
simultaneously explaining neutrino oscillations, inflation, reheating, dark
matter and baryon asymmetry of the Universe. Besides the seesaw mechanism in
neutrino sector, we use only gravity, which solves all the problems by
exploiting scalaron.Comment: 13 pages; v2: minor corrections; v3: 14 pages, journal versio
Towards a Nonequilibrium Quantum Field Theory Approach to Electroweak Baryogenesis
We propose a general method to compute -violating observables from
extensions of the standard model in the context of electroweak baryogenesis. It
is alternative to the one recently developed by Huet and Nelson and relies on a
nonequilibrium quantum field theory approach. The method is valid for all
shapes and sizes of the bubble wall expanding in the thermal bath during a
first-order electroweak phase transition. The quantum physics of -violation
and its suppression coming from the incoherent nature of thermal processes are
also made explicit.Comment: 19 pages, 1 figure available upon e-mail reques
Statistics of Cosmological Inhomogeneities
This contribution to the Proceedings is based on the talk given at the
Conference on Birth of the Universe and Fundamental Physics, Rome, May 18-21,
1994. Some selected topics of the subject are reviewed: Models of Primordial
Fluctuations; Reconstruction of the Cosmological Density Probability
Distribution Function (PDF) from Cumulants; PDFs from the Zel'dovich
Approximation and from Summarizing Perturbation Series; Fitting by the
Log-normal Distribution.Comment: 11 pages, 3 figures (available from the author), LaTe
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