262 research outputs found
A perturbative approach for the dynamics of the quantum Zeno subspaces
In this paper we investigate the dynamics of the quantum Zeno subspaces which
are the eigenspaces of the interaction Hamiltonian, belonging to different
eigenvalues. Using the perturbation theory and the adiabatic approximation, we
get a general expression of the jump probability between different Zeno
subspaces. We applied this result in some examples. In these examples, as the
coupling constant of the interactions increases, the measurement keeps the
system remaining in its initial subspace and the quantum Zeno effect takes
place.Comment: 14 pages, 3 figure
Zeno dynamics and constraints
We investigate some examples of quantum Zeno dynamics, when a system
undergoes very frequent (projective) measurements that ascertain whether it is
within a given spatial region. In agreement with previously obtained results,
the evolution is found to be unitary and the generator of the Zeno dynamics is
the Hamiltonian with hard-wall (Dirichlet) boundary conditions. By using a new
approach to this problem, this result is found to be valid in an arbitrary
-dimensional compact domain. We then propose some preliminary ideas
concerning the algebra of observables in the projected region and finally look
at the case of a projection onto a lower dimensional space: in such a situation
the Zeno ansatz turns out to be a procedure to impose constraints.Comment: 21 page
Classical Statistical Mechanics Approach to Multipartite Entanglement
We characterize the multipartite entanglement of a system of n qubits in
terms of the distribution function of the bipartite purity over balanced
bipartitions. We search for maximally multipartite entangled states, whose
average purity is minimal, and recast this optimization problem into a problem
of statistical mechanics, by introducing a cost function, a fictitious
temperature and a partition function. By investigating the high-temperature
expansion, we obtain the first three moments of the distribution. We find that
the problem exhibits frustration.Comment: 38 pages, 10 figures, published versio
Reduced coherence in double-slit diffraction of neutrons
In diffraction experiments with particle beams, several effects lead to a
fringe visibility reduction of the interference pattern. We theoretically
describe the intensity one can measure in a double-slit setup and compare the
results with the experimental data obtained with cold neutrons. Our conclusion
is that for cold neutrons the fringe visibility reduction is due not to
decoherence, but to initial incoherence.Comment: 4 pages LaTeX, 2 figure
Hausdorff clustering of financial time series
A clustering procedure, based on the Hausdorff distance, is introduced and
tested on the financial time series of the Dow Jones Industrial Average (DJIA)
index.Comment: 9 pages, 3 figure
Thermal limitation of far-field matter-wave interference
We assess the effect of the heat radiation emitted by mesoscopic particles on
their ability to show interference in a double slit arrangement. The analysis
is based on a stationary, phase-space based description of matter wave
interference in the presence of momentum-exchange mediated decoherence.Comment: 8 pages, 2 figures; published versio
Zeno physics in ultrastrong circuit QED
We study the Zeno and anti-Zeno effects in a superconducting qubit
interacting strongly and ultrastrongly with a microwave resonator. Using a
model of a frequently measured two-level system interacting with a quantized
mode, we show different behaviors and total control of the Zeno times depending
on whether the rotating-wave approximation can be applied in the
Jaynes-Cummings model, or not. We exemplify showing the strong dependence of
our results with the properties of the initial field states and suggest
applications for quantum tomography.Comment: 5 pages, 3 figure
Radon transform on the cylinder and tomography of a particle on the circle
The tomographic probability distribution on the phase space (cylinder)
related to a circle or an interval is introduced. The explicit relations of the
tomographic probability densities and the probability densities on the phase
space for the particle motion on a torus are obtained and the relation of the
suggested map to the Radon transform on the plane is elucidated. The
generalization to the case of a multidimensional torus is elaborated and the
geometrical meaning of the tomographic probability densities as marginal
distributions on the helix discussed.Comment: 9 pages, 3 figure
Slow relaxation, confinement, and solitons
Millisecond crystal relaxation has been used to explain anomalous decay in
doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons.
Our model exhibits confinement of mechanical energy released by excitation.
Extending the model to long times is justified by its relation to solitons,
excitations previously proposed to occur in alkali halides. Soliton damping and
observation are also discussed
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