840 research outputs found
Quantum catastrophe of slow light
Catastrophes are at the heart of many fascinating optical phenomena. The
rainbow, for example, is a ray catastrophe where light rays become infinitely
intense. The wave nature of light resolves the infinities of ray catastrophes
while drawing delicate interference patterns such as the supernumerary arcs of
the rainbow. Black holes cause wave singularities. Waves oscillate with
infinitely small wave lengths at the event horizon where time stands still. The
quantum nature of light avoids this higher level of catastrophic behaviour
while producing a quantum phenomenon known as Hawking radiation. As this letter
describes, light brought to a standstill in laboratory experiments can suffer a
similar wave singularity caused by a parabolic profile of the group velocity.
In turn, the quantum vacuum is forced to create photon pairs with a
characteristic spectrum. The idea may initiate a theory of quantum
catastrophes, in addition to classical catastrophe theory, and the proposed
experiment may lead to the first direct observation of a phenomenon related to
Hawking radiation.Comment: Published as "A laboratory analogue of the event horizon using slow
light in an atomic medium
Quantum gravity effects on statistics and compact star configurations
The thermodynamics of classical and quantum ideal gases based on the
Generalized uncertainty principle (GUP) are investigated. At low temperatures,
we calculate corrections to the energy and entropy. The equations of state
receive small modifications. We study a system comprised of a zero temperature
ultra-relativistic Fermi gas. It turns out that at low Fermi energy
, the degenerate pressure and energy are lifted. The
Chandrasekhar limit receives a small positive correction. We discuss the
applications on configurations of compact stars. As increases,
the radius, total number of fermions and mass first reach their nonvanishing
minima and then diverge. Beyond a critical Fermi energy, the radius of a
compact star becomes smaller than the Schwarzschild one. The stability of the
configurations is also addressed. We find that beyond another critical value of
the Fermi energy, the configurations are stable. At large radius, the increment
of the degenerate pressure is accelerated at a rate proportional to the radius.Comment: V2. discussions on the stability of star configurations added, 17
pages, 2 figures, typos corrected, version to appear in JHE
Acoustic black holes for relativistic fluids
We derive a new acoustic black hole metric from the Abelian Higgs model. In
the non-relativistic limit, while the Abelian Higgs model becomes the
Ginzburg-Landau model, the metric reduces to an ordinary Unruh type. We
investigate the possibility of using (type I and II) superconductors as the
acoustic black holes. We propose to realize experimental acoustic black holes
by using spiral vortices solutions from the Navier-stokes equation in the
non-relativistic classical fluids.Comment: 16 pages. typos corrected, contents expande
The entangling side of the Unruh-Hawking effect
We show that the Unruh effect can create net quantum entanglement between
inertial and accelerated observers depending on the choice of the inertial
state. This striking result banishes the extended belief that the Unruh effect
can only destroy entanglement and furthermore provides a new and unexpected
source for finding experimental evidence of the Unruh and Hawking effects.Comment: 4 pages, 4 figures. Added Journal referenc
A phenomenological description of quantum-gravity-induced space-time noise
I propose a phenomenological description of space-time foam and discuss the
experimental limits that are within reach of forthcoming experiments.Comment: 10 pages, LaTex, 1 figure. Short paper, omitting most technical
details. More detailed analysis was reported in gr-qc/010400
Vortex nucleation as a case study of symmetry breaking in quantum systems
Mean-field methods are a very powerful tool for investigating weakly
interacting many-body systems in many branches of physics. In particular, they
describe with excellent accuracy trapped Bose-Einstein condensates. A generic,
but difficult question concerns the relation between the symmetry properties of
the true many-body state and its mean-field approximation. Here, we address
this question by considering, theoretically, vortex nucleation in a rotating
Bose-Einstein condensate. A slow sweep of the rotation frequency changes the
state of the system from being at rest to the one containing one vortex. Within
the mean-field framework, the jump in symmetry occurs through a turbulent phase
around a certain critical frequency. The exact many-body ground state at the
critical frequency exhibits strong correlations and entanglement. We believe
that this constitutes a paradigm example of symmetry breaking in - or change of
the order parameter of - quantum many-body systems in the course of adiabatic
evolution.Comment: Minor change
Controlling a magnetic Feshbach resonance with laser light
The capability to tune the strength of the elastic interparticle interaction
is crucial for many experiments with ultracold gases. Magnetic Feshbach
resonances are a tool widely used for this purpose, but future experiments
would benefit from additional flexibility such as spatial modulation of the
interaction strength on short length scales. Optical Feshbach resonances offer
this possibility in principle, but suffer from fast particle loss due to
light-induced inelastic collisions. Here we show that light near-resonant with
a molecular bound-to-bound transition can be used to shift the magnetic field
at which a magnetic Feshbach resonance occurs. This makes it possible to tune
the interaction strength with laser light and at the same time induce
considerably less loss than an optical Feshbach resonance would do
An interferometric gravitational wave detector as a quantum-gravity apparatus
As a consequence of the extreme precision of the measurements it performs, an
interferometric gravitational wave detector is a macroscopic apparatus for
which quantum effects are not negligible. I observe that this property can be
exploited to probe some aspects of the interplay between Quantum Mechanics and
Gravity.Comment: LaTex, 7 pages. Version accepted for publication in Nature. Under
press embargo until publicatio
Coexisting conical bipolar and equatorial outflows from a high-mass protostar
The BN/KL region in the Orion molecular cloud is an archetype in the study of
the formation of stars much more massive than the Sun. This region contains
luminous young stars and protostars, but it is difficult to study because of
overlying dust and gas. Our basic expectations are shaped to some extent by the
present theoretical picture of star formation, the cornerstone of which is that
protostars acrete gas from rotating equatorial disks, and shed angular momentum
by ejecting gas in bipolar outflows. The main source of the outflow in the
BN/KL region may be an object known as radio source I, which is commonly
believed to be surrounded by a rotating disk of molecular material. Here we
report high-resolution observations of silicon monoxide (SiO) and water maser
emission from the gas surrounding source I; we show that within 60 AU (about
the size of the Solar System), the region is dominated by a conical bipolar
outflow, rather than the expected disk. A slower outflow, close to the
equatorial plane of the protostellar system, extends to radii of 1,000 AU.Comment: 10 pages, 2 figures. Accepted by Nature. To appear December 199
Testing A (Stringy) Model of Quantum Gravity
I discuss a specific model of space-time foam, inspired by the modern
non-perturbative approach to string theory (D-branes). The model views our
world as a three brane, intersecting with D-particles that represent stringy
quantum gravity effects, which can be real or virtual. In this picture, matter
is represented generically by (closed or open) strings on the D3 brane
propagating in such a background. Scattering of the (matter) strings off the
D-particles causes recoil of the latter, which in turn results in a distortion
of the surrounding space-time fluid and the formation of (microscopic, i.e.
Planckian size) horizons around the defects. As a mean-field result, the
dispersion relation of the various particle excitations is modified, leading to
non-trivial optical properties of the space time, for instance a non-trivial
refractive index for the case of photons or other massless probes. Such models
make falsifiable predictions, that may be tested experimentally in the
foreseeable future. I describe a few such tests, ranging from observations of
light from distant gamma-ray-bursters and ultra high energy cosmic rays, to
tests using gravity-wave interferometric devices and terrestrial particle
physics experients involving, for instance, neutral kaons.Comment: 25 pages LATEX, four figures incorporated, uses special proceedings
style. Invited talk at the third international conference on Dark Matter in
Astro and Particle Physics, DARK2000, Heidelberg, Germany, July 10-15 200
- âŠ