423 research outputs found
The On-Freezing Phenomenon: Cognitive and Behavioral Aspects
Freezing of gait is a warning sign of Parkinson's disease. One could distinguish off-freezing, which is associated with dopaminergic therapy and to its titration, and it is clinically related to wearing-off phenomenon. Differently, the on-freezing phenomenon seems to be related to a neural disruption of the frontal-parietal-basal ganglia-pontine projections; clinically, it does not respond to therapy modifications or to different drug titration. In a group of patients with on-freezing, we have detected an alteration of focusing attention, an impairment of set-shifting, in addition to poor abstract reasoning and a reduction of planning. These aspects have been even more evident, when compared with the results obtained by a group of PD patients, without freezing
Continuous quantum nondemolition feedback and unconditional atomic spin squeezing
We discuss the theory and experimental considerations of a quantum feedback
scheme for producing deterministically reproducible spin squeezing. Continuous
nondemolition atom number measurement from monitoring a probe field
conditionally squeezes the sample. Simultaneous feedback of the measurement
results controls the quantum state such that the squeezing becomes
unconditional. We find that for very strong cavity coupling and a limited
number of atoms, the theoretical squeezing approaches the Heisenberg limit.
Strong squeezing will still be produced at weaker coupling and even in free
space (thus presenting a simple experimental test for quantum feedback). The
measurement and feedback can be stopped at any time, thereby freezing the
sample with a desired amount of squeezing.Comment: 17 pages, 5 figures, submitted to JP
Quantum Revivals in a Periodically Driven Gravitational Cavity
Quantum revivals are investigated for the dynamics of an atom in a driven
gravitational cavity. It is demonstrated that the external driving field
influences the revival time significantly. Analytical expressions are presented
which are based on second order perturbation theory and semiclassical secular
theory. These analytical results explain the dependence of the revival time on
the characteristic parameters of the problem quantitatively in a simple way.
They are in excellent agreement with numerical results
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