1,057 research outputs found
Purification through Zeno-like Measurements
A series of frequent measurements on a quantum system (Zeno-like
measurements) is shown to result in the ``purification'' of another quantum
system in interaction with the former. Even though the measurements are
performed on the former system, their effect drives the latter into a pure
state, irrespectively of its initial (mixed) state, provided certain conditions
are satisfied.Comment: REVTeX4, 4 pages, 1 figure; to be published in Phys. Rev. Lett.
(2003
Curvature effect on nuclear pasta: Is it helpful for gyroid appearance?
In supernova cores and neutron star crusts, nuclei are thought to deform to
rodlike and slablike shapes, which are often called nuclear pasta. We study the
equilibrium properties of the nuclear pasta by using a liquid drop model with
curvature corrections. It is confirmed that the curvature effect acts to lower
the transition densities between different shapes. We also examine the gyroid
structure, which was recently suggested as a different type of nuclear pasta by
analogy with the polymer systems. The gyroid structure investigated in this
paper is approximately formulated as an extension of the periodic minimal
surface whose mean curvature vanishes. In contrast to our expectations, we find
from the present approximate formulation that the curvature corrections act to
slightly disfavor the appearance of the gyroid structure. By comparing the
energy corrections in the gyroid phase and the hypothetical phases composed of
d-dimensional spheres, where d is a general dimensionality, we show that the
gyroid is unlikely to belong to a family of the generalized dimensional
spheres.Comment: 14 pages, 8 figure
Zeno Dynamics of von Neumann Algebras
The dynamical quantum Zeno effect is studied in the context of von Neumann
algebras. We identify a localized subalgebra on which the Zeno dynamics acts by
automorphisms. The Zeno dynamics coincides with the modular dynamics of that
subalgebra, if an additional assumption is satisfied. This relates the modular
operator of that subalgebra to the modular operator of the original algebra by
a variant of the Kato-Lie-Trotter product formula.Comment: Revised version; further typos corrected; 9 pages, AMSLaTe
Exponential behavior of a quantum system in a macroscopic medium
An exponential behavior at all times is derived for a solvable dynamical
model in the weak-coupling, macroscopic limit. Some implications for the
quantum measurement problem are discussed, in particular in connection with
dissipation.Comment: 8 pages, report BA-TH/94-17
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Quantum Dynamical Model for Wave Function Reduction in Classical and Macroscopic Limits
In this papper, a quantum dynamical model describing the quantum measurement
process is presented as an extensive generalization of the Coleman-Hepp model.
In both the classical limit with very large quantum number and macroscopic
limit with very large particle number in measuring instrument, this model
generally realizes the wave packet collapse in quantum measurement as a
consequence of the Schrodinger time evolution in either the exactly-solvable
case or the non-(exactly-)solvable case.
For the latter, its quasi-adiabatic case is explicitly analysed by making use
of the high-order adiabatic approximation method and then manifests the wave
packet collapse as well as the exactly-solvable case. By highlighting these
analysis, it is finally found that an essence of the dynamical model of wave
packet collapse is the factorization of the Schrodinger evolution other than
the exact solvability. So many dynamical models including the well-known ones
before, which are exactly-solvable or not, can be shown only to be the concrete
realizations of this factorizabilityComment: ITP.SB-93-14,19 page
Reflection and Transmission in a Neutron-Spin Test of the Quantum Zeno Effect
The dynamics of a quantum system undergoing frequent "measurements", leading
to the so-called quantum Zeno effect, is examined on the basis of a
neutron-spin experiment recently proposed for its demonstration. When the
spatial degrees of freedom are duely taken into account, neutron-reflection
effects become very important and may lead to an evolution which is totally
different from the ideal case.Comment: 26 pages, 6 figure
An quantum approach of measurement based on the Zurek's triple model
In a close form without referring the time-dependent Hamiltonian to the total
system, a consistent approach for quantum measurement is proposed based on
Zurek's triple model of quantum decoherence [W.Zurek, Phys. Rev. D 24, 1516
(1981)]. An exactly-solvable model based on the intracavity system is dealt
with in details to demonstrate the central idea in our approach: by peeling off
one collective variable of the measuring apparatus from its many degrees of
freedom, as the pointer of the apparatus, the collective variable de-couples
with the internal environment formed by the effective internal variables, but
still interacts with the measured system to form a triple entanglement among
the measured system, the pointer and the internal environment. As another
mechanism to cause decoherence, the uncertainty of relative phase and its
many-particle amplification can be summed up to an ideal entanglement or an
Shmidt decomposition with respect to the preferred basis.Comment: 22pages,3figure
The various power decays of the survival probability at long times for free quantum particle
The long time behaviour of the survival probability of initial state and its
dependence on the initial states are considered, for the one dimensional free
quantum particle. We derive the asymptotic expansion of the time evolution
operator at long times, in terms of the integral operators. This enables us to
obtain the asymptotic formula for the survival probability of the initial state
, which is assumed to decrease sufficiently rapidly at large .
We then show that the behaviour of the survival probability at long times is
determined by that of the initial state at zero momentum . Indeed,
it is proved that the survival probability can exhibit the various power-decays
like for an arbitrary non-negative integers as ,
corresponding to the initial states with the condition as .Comment: 15 pages, to appear in J. Phys.
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