4,017 research outputs found
Towards experimental entanglement connection with atomic ensembles in the single excitation regime
We present a protocol for performing entanglement connection between pairs of
atomic ensembles in the single excitation regime. Two pairs are prepared in an
asynchronous fashion and then connected via a Bell measurement. The resulting
state of the two remaining ensembles is mapped to photonic modes and a reduced
density matrix is then reconstructed. Our observations confirm for the first
time the creation of coherence between atomic systems that never interacted, a
first step towards entanglement connection, a critical requirement for quantum
networking and long distance quantum communications
Stable and Unstable Regimes of Mass Accretion onto RW Aur A
We present monitoring observations of the active T Tauri star RW Aur, from
2010 October to 2015 January, using optical high-resolution (R>10000)
spectroscopy with CFHT-ESPaDOnS. Optical photometry in the literature shows
bright, stable fluxes over most of this period, with lower fluxes (by 2-3 mag.)
in 2010 and 2014. In the bright period our spectra show clear photospheric
absorption, complicated variation in the Ca II 8542 A emission}profile shapes,
and a large variation in redshifted absorption in the O I 7772 and 8446 A and
He I 5876 A lines, suggesting unstable mass accretion during this period. In
contrast, these line profiles are relatively uniform during the faint periods,
suggesting stable mass accretion. During the faint periods the photospheric
absorption lines are absent or marginal, and the averaged Li I profile shows
redshifted absorption due to an inflow. We discuss (1) occultation by
circumstellar material or a companion and (2) changes in the activity of mass
accretion to explain the above results, together with near-infrared and X-ray
observations from 2011-2015. Neither scenario can simply explain all the
observed trends, and more theoretical work is needed to further investigate
their feasibilities.Comment: 23 pages, 11 figures, 4 tables, accepted by Astrophysical Journal;
some typos corrected on 4/18/201
Quasi-Fermi Distribution and Resonant Tunneling of Quasiparticles with Fractional Charges
We study the resonant tunneling of quasiparticles through an impurity between
the edges of a Fractional Quantum Hall sample. We show that the one-particle
momentum distribution of fractionally charged edge quasiparticles has a
quasi-Fermi character. The density of states near the quasi-Fermi energy at
zero temperature is singular due to the statistical interaction of
quasiparticles. Another effect of this interaction is a new selection rule for
the resonant tunneling of fractionally charged quasiparticles: the resonance is
suppressed unless an integer number of {\em electrons} occupies the impurity.
It allows a new explanation of the scaling behavior observed in the mesoscopic
fluctuations of the conductivity in the FQHE.Comment: 7 pages, REVTeX 3.0, Preprint SU-ITP-93-1
Hydrodynamic modes in a trapped Bose gas above the Bose-Einstein transition
We discuss the collective modes of a trapped Bose gas in the hydrodynamic
regime where atomic collisions ensure local thermal equilibrium for the
distribution function. Starting from the conservation laws, in the linearized
limit we derive a closed equation for the velocity fluctuations in a trapped
Bose gas above the Bose-Einstein transition temperature. Explicit solutions for
a parabolic trap are given. We find that the surface modes have the same
dispersion relation as the one recently obtained by Stringari for the
oscillations of the condensate at within the Thomas-Fermi approximation.
Results are also given for the monopole ``breathing'' mode as well as for the
excitations which result from the coupling of the monopole and quadrupole
modes in an anisotropic parabolic well.Comment: 4 pages, no figure, submitted to Phys. Rev. Let
Measuring response functions of active materials from data
From flocks of birds to biomolecular assemblies, systems in which many
individual components independently consume energy to perform mechanical work
exhibit a wide array of striking behaviors. Methods to quantify the dynamics of
these so called active systems generally aim to extract important length or
time scales from experimental fields. Because such methods focus on extracting
scalar values, they do not wring maximal information from experimental data. We
introduce a method to overcome these limitations. We extend the framework of
correlation functions by taking into account the internal headings of
displacement fields. The functions we construct represent the material response
to specific types of active perturbation within the system. Utilizing these
response functions we query the material response of disparate active systems
composed of actin filaments and myosin motors, from model fluids to living
cells. We show we can extract critical length scales from the turbulent flows
of an active nematic, anticipate contractility in an active gel, distinguish
viscous from viscoelastic dissipation, and even differentiate modes of
contractility in living cells. These examples underscore the vast utility of
this method which measures response functions from experimental observations of
complex active systems
Quantized hydrodynamic model and the dynamic structure factor for a trapped Bose gas
We quantize the recent hydrodynamic analysis of Stringari for the low-energy
collective modes of a trapped Bose gas at . This is based on the
time-dependent Gross-Pitaevskii equation, but omits the kinetic energy of the
density fluctuations. We diagonalize the hydrodynamic Hamiltonian in terms of
the normal modes associated with the amplitude and phase of the inhomogeneous
Bose order parameter. These normal modes provide a convenient basis for
calculating observable quantities. As applications, we calculate the depletion
of the condensate at as well as the inelastic light-scattering cross
section from low-energy condensate fluctuations. The latter
involves a sum over all normal modes, with a weight proportional to the square
of the Fourier component of the density fluctuation associated with a
given mode. Finally, we show how the Thomas-Fermi hydrodynamic description can
be derived starting from the coupled Bogoliubov equations.Comment: 25 pages, 4 figures, submitted to Phys. Rev.
Decoherence in Quantum Gravity: Issues and Critiques
An increasing number of papers have appeared in recent years on decoherence
in quantum gravity at the Planck energy. We discuss the meaning of decoherence
in quantum gravity starting from the common notion that quantum gravity is a
theory for the microscopic structures of spacetime, and invoking some generic
features of quantum decoherence from the open systems viewpoint. We dwell on a
range of issues bearing on this process including the relation between
statistical and quantum, noise from effective field theory, the meaning of
stochasticity, the origin of non-unitarity and the nature of nonlocality in
this and related contexts. To expound these issues we critique on two
representative theories: One claims that decoherence in quantum gravity scale
leads to the violation of CPT symmetry at sub-Planckian energy which is used to
explain today's particle phenomenology. The other uses this process in place
with the Brownian motion model to prove that spacetime foam behaves like a
thermal bath.Comment: 25 pages, proceedings of DICE06 (Piombino
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