65,632 research outputs found
Non-reciprocal few-photon devices based on chiral waveguide-emitter couplings
We demonstrate the possibility of designing efficient, non reciprocal
few-photon devices by exploiting the chiral coupling between two waveguide
modes and a single quantum emitter. We show how this system can induce
non-reciprocal photon transport at the single-photon level and act as an
optical diode. Afterwards, we also show how the same system shows a
transistor-like behaviour for a two-photon input. The efficiency in both cases
is shown to be large for feasible experimental implementations. Our results
illustrate the potential of chiral waveguide-emitter couplings for applications
in quantum circuitry.Comment: Mathematica notebook attached for calculation of detection
probabilitie
N=1 Supersymmetric Yang-Mills on the lattice at strong coupling
We study N=1 supersymmetric SU(N) Yang-Mills theory on the lattice at strong
coupling. Our method is based on the hopping parameter expansion in terms of
random walks, resummed for any value of the Wilson parameter r in the small
hopping parameter region. Results are given for the mesonic (2-gluino) and
fermionic (3-gluino) propagators and spectrum.Comment: Latex file. 43 pages. Minor additional comments, references added,
typos corrected. Accepted for publication in Int. J. Mod. Phys.
Gamma Ray Bursts: Cosmic Rulers for the High-Redshift Universe?
The desire to extend the Hubble Diagram to higher redshifts than the range of
current Type Ia Supernovae observations has prompted investigation into
spectral correlations in Gamma Ray Bursts, in the hope that standard
candle-like properties can be identified. In this paper we discuss the
potential of these new `cosmic rulers' and highlight their limitations by
investigating the constraints that current data can place on an alternative
Cosmological model in the form of Conformal Gravity. By fitting current Type 1a
Supernovae and Gamma Ray Burst (GRB) data to the predicted luminosity distance
redshift relation of both the standard Concordance Model and Conformal Gravity,
we show that currently \emph{neither} model is strongly favoured at high
redshift. The scatter in the current GRB data testifies to the further work
required if GRBs are to cement their place as effective probes of the
cosmological distance scale.Comment: 2 pages, 1 figure (black & white, colour available). To be published
in "Phil. Trans. of the Royal Society" as proceedings from Discussion Meeting
on Gamma Ray Burst
Few-anyon systems in a parabolic dot
The energy levels of two and three anyons in a two-dimensional parabolic
quantum dot and a perpendicular magnetic field are computed as power series in
1/|J|, where J is the angular momentum. The particles interact repulsively
through a coulombic (1/r) potential. In the two-anyon problem, the reached
accuracy is better than one part in 10^5. For three anyons, we study the
combined effects of anyon statistics and coulomb repulsion in the ``linear''
anyonic states.Comment: LaTeX, 6 pages, 4 postscript figure
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
Line-of-sight velocity distributions of elliptical galaxies from collisionless mergers
We analyse the skewness of the line-of-sight velocity distributions in model
elliptical galaxies built through collisionless galaxy mergers. We build the
models using large N-body simulations of mergers between either two spiral or
two elliptical galaxies. Our aim is to investigate whether the observed ranges
of skewness coefficient (h3) and the rotational support (V/sigma), as well as
the anticorrelation between h3 and V, may be reproduced through collisionless
mergers. Previous attempts using N-body simulations failed to reach V/sigma ~
1-2 and corresponding high h3 values, which suggested that gas dynamics and
ensuing star formation might be needed in order to explain the skewness
properties of ellipticals through mergers. Here we show that high V/sigma and
high h3 are reproduced in collisionless spiral-spiral mergers whenever a
central bulge allows the discs to retain some of their original angular
momentum during the merger. We also show that elliptical-elliptical mergers,
unless merging from a high-angular momentum orbit, reproduce the strong
skewness observed in non-rotating, giant, boxy ellipticals. The behaviour of
the h3 coefficient therefore associates rapidly-rotating disky ellipticals to
disc-disc mergers, and associates boxy, slowly-rotating giant ellipticals to
elliptical-elliptical mergers, a framework generally consistent with the
expectations of hierarchical galaxy formation.Comment: 5 pages, 4 figures, MNRAS Letters, in pres
Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles
To gain a better understanding of the inner disc region that comprises active
galactic nuclei it is necessary to understand the pattern in which the disc is
illuminated (the emissivity profile) by X-rays emitted from the continuum
source above the black hole (corona). The differences in the emissivity
profiles produced by various corona geometries are explored via general
relativistic ray tracing simulations. Through the analysis of various
parameters of the geometries simulated it is found that emissivity profiles
produced by point source and extended geometries such as cylindrical slabs and
spheroidal coronae placed on the accretion disc are distinguishable. Profiles
produced by point source and conical geometries are not significantly
different, requiring an analysis of reflection fraction to differentiate the
two geometries. Beamed point and beamed conical sources are also simulated in
an effort to model jet-like coronae, though the differences here are most
evident in the reflection fraction. For a point source we determine an
approximation for the measured reflection fraction with the source height and
velocity. Simulating spectra from the emissivity profiles produced by the
various geometries produce distinguishable differences. Overall spectral
differences between the geometries do not exceed 15 per cent in the most
extreme cases. It is found that emissivity profiles can be useful in
distinguishing point source and extended geometries given high quality spectral
data of extreme, bright sources over long exposure times. In combination with
reflection fraction, timing, and spectral analysis we may use emissivity
profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
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