102 research outputs found
Memory Effects and Scaling Properties of Traffic Flows
Traffic flows are studied in terms of their noise of sound, which is an
easily accessible experimental quantity. The sound noise data is studied making
use of scaling properties of wavelet transforms and Hurst exponents are
extracted. The scaling behavior is used to characterize the traffic flows in
terms of scaling properties of the memory function in Mori-Lee stochastic
differential equations. The results obtained provides for a new theoretical as
well as experimental framework to characterize the large-time behavior of
traffic flows. The present paper outlines the procedure by making use of
one-lane computer simulations as well as sound-data measurements from a real
two-lane traffic flow. We find the presence of conventional diffusion as well
as 1/f-noise in real traffic flows at large time scales.Comment: 3 figure
Rapid Steady State Convergence for Quantum Systems Using Time-Delayed Feedback Control
We propose a time-delayed feedback control scheme for open quantum systems
that can dramatically reduce the time to reach steady state. No measurement is
performed in the feedback loop, and we suggest a simple all-optical
implementation for a cavity QED system. We demonstrate the potential of the
scheme by applying it to a driven and dissipative Dicke model, as recently
realized in a quantum gas experiment. The time to reach steady state can then
reduced by two orders of magnitude for parameters taken from experiment, making
previously inaccessible long time attractors reachable within typical
experimental run times. The scheme also offers the possibility of slowing down
the dynamics, as well as qualitatively changing the phase diagram of the
corresponding physical system.Comment: 25 pages, 9 figures. Invited paper in "Focus on Coherent Control of
Complex Quantum Systems", Eds. B. Whaley and G. Milburn. PS: Preview on OSX
struggles with opening some of the figures with a lot of data in the
Theory of the Microscopic Maser Phase Transitions
Phase diagrams of the micromaser system are mapped out in terms of the physical parameters at hand like the atom cavity transit time, the atom-photon frequency detuning, the number of thermal photons and the probability for a pump atom to be in its excited state. Critical fluctuations are studied in terms of correlation measurements on atoms having passed through the micromaser or on the microcavity photons themselves. At sufficiently large values of the detuning we find a ``twinkling'' mode of the micromaser system. Detailed properties of the trapping states are also presented
Collective Two-Atom Effects and Trapping States in the Micromaser
We investigate signals of trapping states in the micromaser system in terms
of the average number of cavity photons as well as a suitably defined
correlation length of atoms leaving the cavity. In the description of
collective two-atom effects we allow the mean number of pump atoms inside the
cavity during the characteristic atomic cavity transit time to be as large as
of order one. The master equation we consider, which describes the micromaser
including collective two-atom effects, still exhibits trapping states for even
for a mean number of atoms inside the cavity close to one. We, however, argue
more importantly that the trapping states are more pronounced in terms of the
correlation length as compared to the average number of cavity photons, i.e. we
suggest that trapping states can be more clearly revealed experimentally in
terms of the atom correlation length. For axion detection in the micromaser
this observable may therefore be an essential ingredient.Comment: 5 figure
On the Preparation of Pure States in Resonant Microcavities
We consider the time evolution of the radiation field (R) and a two-level
atom (A) in a resonant microcavity in terms of the Jaynes-Cummings model with
an initial general pure quantum state for the radiation field. It is then
shown, using the Cauchy-Schwarz inequality and also a Poisson resummation
technique, that {\it perfect} coherence of the atom can in general never be
achieved. The atom and the radiation field are, however, to a good
approximation in a pure state in the middle of what
has been traditionally called the ``collapse region'', independent of the
initial state of the atoms, provided that the initial pure state of the
radiation field has a photon number probability distribution which is
sufficiently peaked and phase differences that do not vary significantly around
this peak. An approximative analytic expression for the quantity
\Tr[\rho^2_{A}(t)], where is the reduced density matrix for the
atom, is derived. We also show that under quite general circumstances an
initial entangled pure state will be disentangled to the pure state .Comment: 14 pages and 3 figure
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