3,471 research outputs found
Deterministic Dicke state preparation with continuous measurement and control
We characterize the long-time projective behavior of the stochastic master
equation describing a continuous, collective spin measurement of an atomic
ensemble both analytically and numerically. By adding state based feedback, we
show that it is possible to prepare highly entangled Dicke states
deterministically.Comment: Additional information is available at
http://minty.caltech.edu/Ensemble
Scattering of polarized laser light by an atomic gas in free space: a QSDE approach
We propose a model, based on a quantum stochastic differential equation
(QSDE), to describe the scattering of polarized laser light by an atomic gas.
The gauge terms in the QSDE account for the direct scattering of the laser
light into different field channels. Once the model has been set, we can
rigorously derive quantum filtering equations for balanced polarimetry and
homodyne detection experiments, study the statistics of output processes and
investigate a strong driving, weak coupling limit.Comment: 9 pages, 2 figure
States for phase estimation in quantum interferometry
Ramsey interferometry allows the estimation of the phase of rotation
of the pseudospin vector of an ensemble of two-state quantum systems. For
small, the noise-to-signal ratio scales as the spin-squeezing parameter
, with possible for an entangled ensemble. However states with
minimum are not optimal for single-shot measurements of an arbitrary
phase. We define a phase-squeezing parameter, , which is an appropriate
figure-of-merit for this case. We show that (unlike the states that minimize
), the states that minimize can be created by evolving an
unentangled state (coherent spin state) by the well-known 2-axis
counter-twisting Hamiltonian. We analyse these and other states (for example
the maximally entangled state, analogous to the optical "NOON" state ) using several different properties, including ,
, the coefficients in the pseudo angular momentum basis (in the three
primary directions) and the angular Wigner function . Finally
we discuss the experimental options for creating phase squeezed states and
doing single-shot phase estimation.Comment: 8 pages and 5 figure
Extended emission-line regions in low-redshift quasars: Dependence on nuclear spectral properties
We searched for the presence of extended emission-line regions (EELRs) around
low-redshift QSOs. We observed a sample of 20 mainly radio-quiet low-redshift
quasars (z<0.3) by means of integral field spectroscopy. After decomposing the
extended and nuclear emission components, we constructed [OIII] 5007
narrow-band images of the EELR to measure the total flux. From the same data we
obtained high S/N (>50) nuclear spectra to measure properties such as
[OIII]/Hbeta flux ratios, FeII equivalent widths and Hbeta line widths. A
significant fraction of the quasars (8/20) show a luminous EELR, with detected
linear sizes of several kpc. Whether or not a QSO has a luminous EELR is
strongly related with nuclear properties, in the sense that an EELR was
detected in objects with low FeII equivalent width and large Hbeta FWHM. The
EELRs were detected preferentially in QSOs with larger black hole masses. There
is no discernible relation, however, between EELR detection and QSO luminosity
and Eddington ratio.Comment: 4 pages, 4 figures, accepted for publication in A&
A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies: Paper I
We present the first results from a major HST WFPC2 imaging study aimed at
providing the first statistically meaningful comparison of the morphologies,
luminosities, scalelengths and colours of the host galaxies of radio-quiet
quasars, radio-loud quasars, and radio galaxies. We describe the design of this
study and present the images which have been obtained for the first half of our
33-source sample. We find that the hosts of all three classes of luminous AGN
are massive elliptical galaxies, with scalelengths ~=10 kpc, and R-K colours
consistent with mature stellar populations. Most importantly this is the the
first unambiguous evidence that, just like radio-loud quasars, essentially all
radio-quiet quasars brighter than M_R = -24 reside in massive ellipticals. This
result removes the possibility that radio `loudness' is directly linked to host
galaxy morphology, but is however in excellent accord with the
black-hole/spheroid mass correlation recently highlighted by Magorrian et al.
(1998). We apply the relations given by Magorrian et al. to infer the expected
Eddington luminosity of the putative black hole at the centre of each of the
spheroidal host galaxies we have uncovered. Comparison with the actual nuclear
R-band luminosities suggests that the black holes in most of these galaxies are
radiating at a few percent of the Eddington luminosity; the brightest host
galaxies in our low-z sample are capable of hosting quasars with M_R = -28,
comparable to the most luminous quasars at z = 3. Finally we discuss our
host-derived black-hole masses in the context of the
radio-luminosity:black-hole mass correlation recently uncovered for nearby
galaxies by Franceschini et al. (1998), and the resulting implications for the
physical origin of radio loudness.Comment: Submitted for publication in the Astrophysical Journal, 55 pages of
latex, plus 12 postscript figures (Figures 1a-1s (greyscales of images and
model fits, and Figures 2a-2g (luminosity profiles and model fits) can be
downloaded from http://www.roe.ac.uk/astronomy/html/rjm1.shtml
Characterizing the entanglement of symmetric many-particle spin-1/2 systems
Analyzing the properties of entanglement in many-particle spin-1/2 systems is
generally difficult because the system's Hilbert space grows exponentially with
the number of constituent particles, . Fortunately, it is still possible to
investigate many-particle entanglement when the state of the system possesses
sufficient symmetry. In this paper, we present a practical method for
efficiently computing various bipartite entanglement measures for states in the
symmetric subspace and perform these calculations for . By
considering all possible bipartite splits, we construct a picture of the
multiscale entanglement in large symmetric systems. In particular, we
characterize dynamically generated spin-squeezed states by comparing them to
known reference states (e.g., GHZ and Dicke states) and new families of states
with near-maximal bipartite entropy. We quantify the trade-off between the
degree of entanglement and its robustness to particle loss, emphasizing that
substantial entanglement need not be fragile.Comment: Updated version reflects changes made in January 200
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Recognition, assessment and treatment of social anxiety disorder: summary of NICE guidance
Social anxiety disorder is one of the most persistent and common of the anxiety disorders, with lifetime prevalence rates in Europe of 6.7% (range 3.9-13.7%).1 It often coexists with depression, substance use disorder, generalised anxiety disorder, panic disorder, and post-traumatic stress disorder.2 It can severely impair a person’s daily functioning by impeding the formation of relationships, reducing quality of life, and negatively affecting performance at work or school. Despite this, and the fact that effective treatments exist, only about half of people with this condition seek treatment, many after waiting 10-15 years.3 Although about 40% of those who develop the condition in childhood or adolescence recover before adulthood,4 for many the disorder persists into adulthood, with the chance of spontaneous recovery then limited compared with other mental health problems.
This article summarises the most recent recommendations from the National Institute for Health and Care Excellence (NICE) on recognising, assessing, and treating social anxiety disorder in children, young people, and adults.
Mapping the ionised gas around the luminous QSO HE 1029-1401: Evidence for minor merger events?
We present VIMOS integral field spectroscopy of the brightest radio-quiet QSO
on the southern sky HE 1029-1401 at a redshift of z=0.086. Standard
decomposition techniques for broad-band imaging are extended to integral field
data in order to deblend the QSO and host emission. We perform a tentative
analysis of the stellar continuum finding a young stellar population (<100Myr)
or a featureless continuum embedded in an old stellar population (10Gyr)
typical for a massive elliptical galaxy. The stellar velocity dispersion of
sigma_*=320\pm90 km/s and the estimated black hole mass
log(M_BH/M_sun)=8.7\pm0.3 are consistent with the local M_BH-sigma_* relation
within the errors. For the first time we map the two-dimensional ionised gas
distribution and the gas velocity field around HE 1029-1401. While the stellar
host morphology is purely elliptical we find a highly structured distribution
of ionised gas out to 16 kpc from the QSO. The gas is highly ionised solely by
the QSO radiation and has a significantly lower metallicity than would be
expected for the stellar mass of the host, indicating an external origin of the
gas most likely due to minor mergers. We find a rotating gas disc around the
QSO and a dispersion-dominated non-rotating gas component within the central 3
kpc. At larger distances the velocity field is heavily disturbed, which could
be interpreted as another signature of past minor merger events. Alternatively,
the arc-like structure seen in the ionised gas might also be indicative of a
large-scale expanding bubble, centred on and possibly driven by the active
nucleus.Comment: 13 pages, 13 figures, 1 table, accepted for publication in A&
Entanglement Sharing in the Two-Atom Tavis-Cummings Model
Individual members of an ensemble of identical systems coupled to a common
probe can become entangled with one another, even when they do not interact
directly. We investigate how this type of multipartite entanglement is
generated in the context of a system consisting of two two-level atoms
resonantly coupled to a single mode of the electromagnetic field. The dynamical
evolution is studied in terms of the entanglements in the different bipartite
partitions of the system, as quantified by the I-tangle. We also propose a
generalization of the so-called residual tangle that quantifies the inherent
three-body correlations in our tripartite system. This enables us to completely
characterize the phenomenon of entanglement sharing in the case of the two-atom
Tavis-Cummings model, a system of both theoretical and experimental interest.Comment: 11 pages, 4 figures, submitted to PRA, v3 contains corrections to
small error
Reverse quantum state engineering using electronic feedback loops
We propose an all-electronic technique to manipulate and control interacting
quantum systems by unitary single-jump feedback conditioned on the outcome of a
capacitively coupled electrometer and in particular a single-electron
transistor. We provide a general scheme to stabilize pure states in the quantum
system and employ an effective Hamiltonian method for the quantum master
equation to elaborate on the nature of stabilizable states and the conditions
under which state purification can be achieved. The state engineering within
the quantum feedback scheme is shown to be linked with the solution of an
inverse eigenvalue problem. Two applications of the feedback scheme are
presented in detail: (i) stabilization of delocalized pure states in a single
charge qubit and (ii) entanglement stabilization in two coupled charge qubits.
In the latter example we demonstrate the stabilization of a maximally entangled
Bell state for certain detector positions and local feedback operations.Comment: 23 pages, 6 figures, to be published by New Journal of Physics (2013
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