1,774 research outputs found
Spin Squeezing under Non-Markovian Channels by Hierarchy Equation Method
We study spin squeezing under non-Markovian channels, and consider an
ensemble of independent spin-1/2 particles with exchange symmetry. Each
spin interacts with its own bath, and the baths are independent and identical.
For this kind of open system, the spin squeezing under decoherence can be
investigated from the dynamics of the local expectations, and the multi-qubit
dynamics can be reduced into the two-qubit one. The reduced dynamics is
obtained by the hierarchy equation method, which is a exact without
rotating-wave and Born-Markov approximation. The numerical results show that
the spin squeezing displays multiple sudden vanishing and revival with lower
bath temperature, and it can also vanish asymptotically.Comment: 7 pages, 4 figure
Output entanglement and squeezing of two-mode fields generated by a single atom
A single four-level atom interacting with two-mode cavities is investigated.
Under large detuning condition, we obtain the effective Hamiltonian which is
unitary squeezing operator of two-mode fields. Employing the input-output
theory, we find that the entanglement and squeezing of the output fields can be
achieved. By analyzing the squeezing spectrum, we show that asymmetric detuning
and asymmetric atomic initial state split the squeezing spectrum from one
valley into two minimum values, and appropriate leakage of the cavity is needed
for obtaining output entangled fields
Lyapunov exponent of the random frequency oscillator: cumulant expansion approach
We consider a one-dimensional harmonic oscillator with a random frequency,
focusing on both the standard and the generalized Lyapunov exponents,
and respectively. We discuss the numerical difficulties that
arise in the numerical calculation of in the case of strong
intermittency. When the frequency corresponds to a Ornstein-Uhlenbeck process,
we compute analytically by using a cumulant expansion including
up to the fourth order. Connections with the problem of finding an analytical
estimate for the largest Lyapunov exponent of a many-body system with smooth
interactions are discussed.Comment: 6 pages, 4 figures, to appear in J. Phys. Conf. Series - LAWNP0
First Passage and Cooperativity of Queuing Kinetics
We model the kinetics of ligand-receptor systems, where multiple ligands may
bind and unbind to the receptor, either randomly or in a specific order.
Equilibrium occupation and first occurrence of complete filling of the receptor
are determined and compared. At equilibrium, receptors that bind ligands
sequentially are more likely to be saturated than those that bind in random
order. Surprisingly however, for low cooperativity, the random process first
reaches full occupancy faster than the sequential one. This is true {\it
except} near a critical binding energy where a 'kinetic trap' arises and the
random process dramatically slows down when the number of binding sites . These results demonstrate the subtle interplay between cooperativity and
sequentiality for a wide class of kinetic phenomena, including chemical
binding, nucleation, and assembly line strategies.Comment: 5pp, 5 figure
Suppression of decoherence by bath ordering
The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an
extended model of the Tessieri-Wilkie Hamiltonian \cite{TWmodel}. The pair of
spins served as an open subsystem were prepared in one of the Bell states and
the bath consisted of some spins-1/2 is in a thermal equilibrium state from the
very beginning. It is found that with the increasing the coupling strength of
the bath spins, the bath forms a resonant antiferromagnetic order. The
polarization correlation between the two spins of the subsystem and the
concurrence are recovered in some extent to the isolated subsystem. This
suppression of the subsystem decoherence may be used to control the quantum
devices in practical applications.Comment: 32 pages, Chinese Physics (accepted
Real Space Renormalization Group for Langevin Dynamics in Absence of Translational Invariance
A novel exact dynamical real space renormalization group for a Langevin
equation derivable from a Euclidean Gaussian action is presented. It is
demonstrated rigorously that an algebraic temporal law holds for the Green
function on arbitrary structures of infinite extent. In the case of fractals it
is shown on specific examples that two different fixed points are found at
variance with periodic structures. Connection with growth dynamics of
interfaces is also discussed.Comment: 22 pages, RevTex 3.0, 5 figures available upon request from
[email protected], to be published in J.Stat.Phy
Fast flowing populations are not well mixed
In evolutionary dynamics, well-mixed populations are almost always associated
with all-to-all interactions; mathematical models are based on complete graphs.
In most cases, these models do not predict fixation probabilities in groups of
individuals mixed by flows. We propose an analytical description in the
fast-flow limit. This approach is valid for processes with global and local
selection, and accurately predicts the suppression of selection as competition
becomes more local. It provides a modelling tool for biological or social
systems with individuals in motion.Comment: 19 pages, 8 figure
Interrelations between Stochastic Equations for Systems with Pair Interactions
Several types of stochastic equations are important in thermodynamics,
chemistry, evolutionary biology, population dynamics and quantitative social
science. For systems with pair interactions four different types of equations
are derived, starting from a master equation for the state space: First,
general mean value and (co)variance equations. Second, Boltzmann-like
equations. Third, a master equation for the configuration space allowing
transition rates which depend on the occupation numbers of the states. Fourth,
a Fokker-Planck equation and a ``Boltzmann-Fokker-Planck equation''. The
interrelations of these equations and the conditions for their validity are
worked out clearly. A procedure for a selfconsistent solution of the nonlinear
equations is proposed. Generalizations to interactions between an arbitrary
number of systems are discussed.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
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