17 research outputs found
Quantum chaos algorithms and dissipative decoherence with quantum trajectories
Using the methods of quantum trajectories we investigate the effects of
dissipative decoherence in a quantum computer algorithm simulating dynamics in
various regimes of quantum chaos including dynamical localization, quantum
ergodic regime and quasi-integrable motion.
As an example we use the quantum sawtooth algorithm which can be implemented
in a polynomial number of quantum gates.
It is shown that the fidelity of quantum computation decays exponentially
with time and that the decay rate is proportional to the number of qubits,
number of quantum gates and per gate dissipation rate induced by external
decoherence.
In the limit of strong dissipation the quantum algorithm generates a quantum
attractor which may have complex or simple structure.
We also compare the effects of dissipative decoherence with the effects of
static imperfections.Comment: 6 pages, 6 figs, research at http://www.quantware.ups-tlse.f
Generation of spatial antibunching with free propagating twin beams
We propose and implement a novel method to produce a spatial anti-bunched
field with free propagating twin beams from spontaneous parametric
down-conversion. The method consists in changing the spatial propagation by
manipulating the transverse degrees of freedom through reflections of one of
the twin beams. Our method use reflective elements eliminating losses from
absorption by the objects inserted in the beams.Comment: Submitted for publication in Phys. Rev.
Thermal properties of spacetime foam
Spacetime foam can be modeled in terms of nonlocal effective interactions in
a classical nonfluctuating background. Then, the density matrix for the
low-energy fields evolves, in the weak-coupling approximation, according to a
master equation that contains a diffusion term. Furthermore, it is argued that
spacetime foam behaves as a quantum thermal field that, apart from inducing
loss of coherence, gives rise to effects such as gravitational Lamb and Stark
shifts as well as quantum damping in the evolution of the low-energy
observables. These effects can be, at least in principle, experimentally
tested.Comment: RevTeX 3.01, 11 pages, no figure