214 research outputs found
Parametric Oscillation with Squeezed Vacuum Reservoirs
Employing the quantum Hamiltonian describing the interaction of two-mode
light (signal-idler modes) generated by a nondegenerate parametric oscillator
(NDPO) with two uncorrelated squeezed vacuum reservoirs (USVR), we derive the
master equation. The corresponding Fokker-Planck equation for the Q-function is
then solved employing a propagator method developed in Ref. \cite{1}. Making
use of this Q-function, we calculate the quadrature fluctuations of the optical
system. From these results we infer that the signal-idler modes are in squeezed
states and the squeezing occurs in the first quadrature. When the NDPO operates
below threshold we show that, for a large squeezing parameter, a squeezing
amounting to a noise suppression approaching 100% below the vacuum level in the
first quadrature can be achieved.Comment: 16 page
Squeezing spectra from s-ordered quasiprobability distributions. Application to dispersive optical bistability
It is well known that the squeezing spectrum of the field exiting a nonlinear
cavity can be directly obtained from the fluctuation spectrum of normally
ordered products of creation and annihilation operators of the cavity mode. In
this article we show that the output field squeezing spectrum can be derived
also by combining the fluctuation spectra of any pair of s-ordered products of
creation and annihilation operators. The interesting result is that the
spectrum obtained in this way from the linearized Langevin equations is exact,
and this occurs in spite of the fact that no s-ordered quasiprobability
distribution verifies a true Fokker-Planck equation, i.e., the Langevin
equations used for deriving the squeezing spectrum are not exact. The
(linearized) intracavity squeezing obtained from any s-ordered distribution is
also exact. These results are exemplified in the problem of dispersive optical
bistability.Comment: 15 pages, no figures, to be published in Journal of Modern Optic
Steps in the bacterial flagellar motor
The bacterial flagellar motor is a highly efficient rotary machine used by
many bacteria to propel themselves. It has recently been shown that at low
speeds its rotation proceeds in steps [Sowa et al. (2005) Nature 437,
916--919]. Here we propose a simple physical model that accounts for this
stepping behavior as a random walk in a tilted corrugated potential that
combines torque and contact forces. We argue that the absolute angular position
of the rotor is crucial for understanding step properties, and show this
hypothesis to be consistent with the available data, in particular the
observation that backward steps are smaller on average than forward steps. Our
model also predicts a sublinear torque-speed relationship at low torque, and a
peak in rotor diffusion as a function of torque
OA05-01. In vivo electroporation enhances the immunogenicity of ADVAX, a DNA-based HIV-1 vaccine candidate, in healthy volunteers
Out-of-equilibrium physics in driven dissipative coupled resonator arrays
Coupled resonator arrays have been shown to exhibit interesting many- body
physics including Mott and Fractional Hall states of photons. One of the main
differences between these photonic quantum simulators and their cold atoms
coun- terparts is in the dissipative nature of their photonic excitations. The
natural equi- librium state is where there are no photons left in the cavity.
Pumping the system with external drives is therefore necessary to compensate
for the losses and realise non-trivial states. The external driving here can
easily be tuned to be incoherent, coherent or fully quantum, opening the road
for exploration of many body regimes beyond the reach of other approaches. In
this chapter, we review some of the physics arising in driven dissipative
coupled resonator arrays including photon fermionisa- tion, crystallisation, as
well as photonic quantum Hall physics out of equilibrium. We start by briefly
describing possible experimental candidates to realise coupled resonator arrays
along with the two theoretical models that capture their physics, the
Jaynes-Cummings-Hubbard and Bose-Hubbard Hamiltonians. A brief review of the
analytical and sophisticated numerical methods required to tackle these systems
is included.Comment: Chapter that appeared in "Quantum Simulations with Photons and
Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by
D.G.Angelakis, Quantum Science and Technology Series, Springer 201
Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond
We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the models and the methods of treatment of such systems, we discuss in detail,
which challenges of condensed matter physics can be addressed with (i)
disordered ultracold lattice gases, (ii) frustrated ultracold gases, (iii)
spinor lattice gases, (iv) lattice gases in "artificial" magnetic fields, and,
last but not least, (v) quantum information processing in lattice gases. For
completeness, also some recent progress related to the above topics with
trapped cold gases will be discussed.Comment: Review article. v2: published version, 135 pages, 34 figure
Maximum likelihood based analysis of equally spaced longitudinal count data with first-order antedependence and overdispersion
Struggles over access to the Muslim public sphere: Multiple publics and discourses on agency, belonging and citizenship (Introduction to the Themed Section)
Abstract This introductory essay provides the context for the articles in this Themed
Section. Despite the diversity in locations, historical backgrounds and contemporary
processes of change, all contributors to this Themed Section focus on the struggle of
Muslim groups over access to an emergent Muslim public sphere. They highlight the
contestations of and shifts in the notions of agency, belonging, and citizenship in
nation-states with Muslim communities within its borders. The introduction consists
of two parts. The first part reviews the notion of the public sphere as conceptualized by
Habermas and critiqued by scholars of a diversity of backgrounds. In relation to the
concept of the Muslim public sphere, three aspects of critique are given closer
c
Lattice Boltzmann simulations of soft matter systems
This article concerns numerical simulations of the dynamics of particles
immersed in a continuum solvent. As prototypical systems, we consider colloidal
dispersions of spherical particles and solutions of uncharged polymers. After a
brief explanation of the concept of hydrodynamic interactions, we give a
general overview over the various simulation methods that have been developed
to cope with the resulting computational problems. We then focus on the
approach we have developed, which couples a system of particles to a lattice
Boltzmann model representing the solvent degrees of freedom. The standard D3Q19
lattice Boltzmann model is derived and explained in depth, followed by a
detailed discussion of complementary methods for the coupling of solvent and
solute. Colloidal dispersions are best described in terms of extended particles
with appropriate boundary conditions at the surfaces, while particles with
internal degrees of freedom are easier to simulate as an arrangement of mass
points with frictional coupling to the solvent. In both cases, particular care
has been taken to simulate thermal fluctuations in a consistent way. The
usefulness of this methodology is illustrated by studies from our own research,
where the dynamics of colloidal and polymeric systems has been investigated in
both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures,
76 page
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