2,591 research outputs found
Information-theory-based solution of the inverse problem in classical statistical mechanics
We present a procedure for the determination of the interaction potential
from the knowledge of the radial pair distribution function. The method,
realized inside an inverse Monte Carlo simulation scheme, is based on the
application of the Maximum Entropy Principle of information theory and the
interaction potential emerges as the asymptotic expression of the transition
probability. Results obtained for high density monoatomic fluids are very
satisfactory and provide an accurate extraction of the potential, despite a
modest computational effort.Comment: 9 pages, 2 figure
A Micro-glitch in the Millisecond Pulsar B1821-24 in M28
We report on the observation of a very small glitch observed for the first
time in a millisecond pulsar, PSR B1821-24 located in the globular cluster M28.
Timing observations were mainly conducted with the Nancay radiotelescope
(France) and confirmation comes from the 140ft radiotelescope at Green Bank and
the new Green Bank Telescope data. This event is characterized by a rotation
frequency step of 3 nHz, or 10^-11 in fractional frequency change along with a
short duration limited to a few days or a week. A marginally significant
frequency derivative step was also found. This glitch follows the main
characteristics of those in the slow period pulsars, but is two orders of
magnitude smaller than the smallest ever recorded. Such an event must be very
rare for millisecond pulsars since no other glitches have been detected when
the cumulated number of years of millisecond pulsar timing observations up to
2001 is around 500 for all these objects. However, pulsar PSR B1821-24 is one
of the youngest among the old recycled ones and there is likely a correlation
between age, or a related parameter, and timing noise. While this event happens
on a much smaller scale, the required adjustment of the star to a new
equilibrium figure as it spins down is a likely common cause for all glitches.Comment: Accepted by ApJ Letters, 5 pages, 2 figures, LaTex (uses
emulateapj.sty
Ultra-Efficient Cooling of Resonators: Beating Sideband Cooling with Quantum Control
The present state-of-the-art in cooling mechanical resonators is a version of
"sideband" cooling. Here we present a method that uses the same configuration
as sideband cooling --- coupling the resonator to be cooled to a second
microwave (or optical) auxiliary resonator --- but will cool significantly
colder. This is achieved by varying the strength of the coupling between the
two resonators over a time on the order of the period of the mechanical
resonator. As part of our analysis, we also obtain a method for fast,
high-fidelity quantum information-transfer between resonators.Comment: 4 pages, revtex4-1, 2 png figure
Improving the Sunscreen Properties of TiO2 through an Understanding of Its Catalytic Properties
The use of particulate titanium dioxide (TiO2) as an active sunscreen ingredient has raised concerns about potential risks from TiO2-mediated free radical formation. To date, remediation attempts have concentrated on reducing the yield of free radical generation by TiO2 upon sunlight exposure. The problem with this approach is that given the band gap in TiO2, production of radical and the ensuing reactive oxygen species (ROS) is completely normal. Our strategy is based on a nontoxic, biocompatible shell that neutralizes the free radicals by scavenging them with natural antioxidants before they exit the particle. The new lignin@TiO2 composites preserve the scattering and absorption properties of TiO2 because the particles retain their nanoscale dimensions as preferred by the cosmetic industry. Although the target properties for photocatalysis and sun-protection applications are opposite, we argue that exactly the same knowledge is required to optimize either one
Quantum measurement of a mesoscopic spin ensemble
We describe a method for precise estimation of the polarization of a
mesoscopic spin ensemble by using its coupling to a single two-level system.
Our approach requires a minimal number of measurements on the two-level system
for a given measurement precision. We consider the application of this method
to the case of nuclear spin ensemble defined by a single electron-charged
quantum dot: we show that decreasing the electron spin dephasing due to nuclei
and increasing the fidelity of nuclear-spin-based quantum memory could be
within the reach of present day experiments.Comment: 8 pages, 2 figures; minor changes, published versio
Mental, Social and Visual Alienation in DâAlessandroâs Photography
This chapter analyzes the first of several photobooks that illustrated the reform of psychiatric health care in Italy in the 1960s and 1970s: Luciano DâAlessandroâs 1969 Gli esclusi. In 1967, DâAlessandro was invited by the director of the asylum of Nocera Superiore, Sergio Piro, to document through photography the abysmal conditions of the âtotal institutionâ that was the pre-reform mental hospital. DâAlessandro first published a small selection of photos, in Popular Photography Italiana (1967), which he then expanded in Gli esclusi. This chapter claims that, in the evolution between the two publications, we can read the complex and multilayered notion of alienation that informed the work of reform, especially that of one of the most famous figures associated with it, Franco Basaglia. By analyzing DâAlessandroâs Gli esclusi through the notion of alienation, this chapter lets what Sekula calls the conditions of âreadabilityâ of the photographic message emerge
Continuous quantum feedback of coherent oscillations in a solid-state qubit
We have analyzed theoretically the operation of the Bayesian quantum feedback
of a solid-state qubit, designed to maintain perfect coherent oscillations in
the qubit for arbitrarily long time. In particular, we have studied the
feedback efficiency in presence of dephasing environment and detector
nonideality. Also, we have analyzed the effect of qubit parameter deviations
and studied the quantum feedback control of an energy-asymmetric qubit.Comment: 11 page
Time-optimal rotation of a spin 1/2: application to the NV center spin in diamond
We study the applicability of the time optimal bang-bang control designed for
spin-1/2 [U. Boscain and P. Mason, J. Math. Phys. {\bf 47}, 062101 (2006)] to
the rotation of the electron spin of a nitrogen-vacancy (NV) center in diamond.
The spin of the NV center is a three-level system, with two levels forming a
relevant qubit subspace where the time-varying magnetic control field performs
rotation, and the third level being idle. We find that the bang-bang control
protocol decreases the rotation time by 20--25% in comparison with the
traditional oscillating sinusoidal driving. We also find that for most values
of the bias field the leakage to the idle level is very small, so that the NV
center is a suitable testbed for experimental study of the time-optimal
protocols. For some special values of the bias field, however, the unwanted
leakage is greatly increased. We demonstrate that this is caused by the
resonance with higher-order Fourier harmonics of the bang-bang driving field.Comment: 6 pages, 4 figure
Quantum-to-Classical Correspondence and Hubbard-Stratonovich Dynamical Systems, a Lie-Algebraic Approach
We propose a Lie-algebraic duality approach to analyze non-equilibrium
evolution of closed dynamical systems and thermodynamics of interacting quantum
lattice models (formulated in terms of Hubbard-Stratonovich dynamical systems).
The first part of the paper utilizes a geometric Hilbert-space-invariant
formulation of unitary time-evolution, where a quantum Hamiltonian is viewed as
a trajectory in an abstract Lie algebra, while the sought-after evolution
operator is a trajectory in a dynamic group, generated by the algebra via
exponentiation. The evolution operator is uniquely determined by the
time-dependent dual generators that satisfy a system of differential equations,
dubbed here dual Schrodinger-Bloch equations, which represent a viable
alternative to the conventional Schrodinger formulation. These dual
Schrodinger-Bloch equations are derived and analyzed on a number of specific
examples. It is shown that deterministic dynamics of a closed classical
dynamical system occurs as action of a symmetry group on a classical manifold
and is driven by the same dual generators as in the corresponding quantum
problem. This represents quantum-to-classical correspondence. In the second
part of the paper, we further extend the Lie algebraic approach to a wide class
of interacting many-particle lattice models. A generalized Hubbard-Stratonovich
transform is proposed and it is used to show that the thermodynamic partition
function of a generic many-body quantum lattice model can be expressed in terms
of traces of single-particle evolution operators governed by the dynamic
Hubbard-Stratonovich fields. Finally, we derive Hubbard-Stratonovich dynamical
systems for the Bose-Hubbard model and a quantum spin model and use the
Lie-algebraic approach to obtain new non-perturbative dual descriptions of
these theories.Comment: 25 pages, 1 figure; v2: citations adde
Convergence to equilibrium for many particle systems
The goal of this paper is to give a short review of recent results of the
authors concerning classical Hamiltonian many particle systems. We hope that
these results support the new possible formulation of Boltzmann's ergodicity
hypothesis which sounds as follows. For almost all potentials, the minimal
contact with external world, through only one particle of , is sufficient
for ergodicity. But only if this contact has no memory. Also new results for
quantum case are presented
- âŠ