158,890 research outputs found
Optimized Double-well quantum interferometry with Gaussian squeezed-states
A Mach-Zender interferometer with a gaussian number-difference squeezed input
state can exhibit sub-shot-noise phase resolution over a large phase-interval.
We obtain the optimal level of squeezing for a given phase-interval
and particle number , with the resulting phase-estimation
uncertainty smoothly approaching as approaches 10/N,
achieved with highly squeezed states near the Fock regime. We then analyze an
adaptive measurement scheme which allows any phase on to be
measured with a precision of requiring only a few measurements, even
for very large . We obtain an asymptotic scaling law of , resulting in a final
precision of . This scheme can be readily implemented in a
double-well Bose-Einstein condensate system, as the optimal input states can be
obtained by adiabatic manipulation of the double-well ground state.Comment: updated versio
Super-rigidity for CR embeddings of real hypersurfaces into hyperquadrics
Let Q^N_l\subset \bC\bP^{N+1} denote the standard real, nondegenerate
hyperquadric of signature and M\subset \bC^{n+1} a real, Levi
nondegenerate hypersurface of the same signature . We shall assume that
there is a holomorphic mapping H_0\colon U\to \bC\bP^{N_0+1}, where is
some neighborhood of in \bC^{n+1}, such that
but . We show that if then, for any , any holomorphic mapping H\colon U\to \bC\bP^{N+1} with and must be the standard linear embedding
of into up to conjugation by automorphisms of
and
Collisions of Jets of Particles from Active Galactic Nuclei with Neutralino Dark Matter
We examine the possibility that energetic Standard Model particles contained
in the jets produced by active galactic nuclei (AGN) may scatter off of the
dark matter halo which is expected to surround the AGN. In particular, if there
are nearby states in the dark sector which can appear resonantly in the
scattering, the cross section can be enhanced and a distinctive edge feature in
the energy spectrum may appear. We examine bounds on supersymmetric models
which may be obtained from the Fermi Gamma-ray Space Telescope observation of
the nearby AGN Centaurus A.Comment: 20 pages, 9 figures; v2: version published in JCA
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
Degenerate Fermi gas in a combined harmonic-lattice potential
In this paper we derive an analytic approximation to the density of states
for atoms in a combined optical lattice and harmonic trap potential as used in
current experiments with quantum degenerate gases. We compare this analytic
density of states to numerical solutions and demonstrate its validity regime.
Our work explicitly considers the role of higher bands and when they are
important in quantitative analysis of this system. Applying our density of
states to a degenerate Fermi gas we consider how adiabatic loading from a
harmonic trap into the combined harmonic-lattice potential affects the
degeneracy temperature. Our results suggest that occupation of excited bands
during loading should lead to more favourable conditions for realizing
degenerate Fermi gases in optical lattices.Comment: 11 pages, 9 figure
On-demand generation of entanglement of atomic qubits via optical interferometry
The problem of on-demand generation of entanglement between single-atom
qubits via a common photonic channel is examined within the framework of
optical interferometry. As expected, for a Mach-Zehnder interferometer with
coherent laser beam as input, a high-finesse optical cavity is required to
overcome sensitivity to spontaneous emission. We show, however, that with a
twin-Fock input, useful entanglement can in principle be created without
cavity-enhancement. Both approaches require single-photon resolving detectors,
and best results would be obtained by combining both cavity-feedback and
twin-Fock inputs. Such an approach may allow a fidelity of using a
two-photon input and currently available mirror and detector technology. In
addition, we study interferometers based on NOON states and show that they
perform similarly to the twin-Fock states, yet without the need for
high-precision photo-detectors. The present interferometrical approach can
serve as a universal, scalable circuit element for quantum information
processing, from which fast quantum gates, deterministic teleportation,
entanglement swapping , can be realized with the aid of single-qubit
operations.Comment: To be published in PR
Effects of collisions against thermal impurities in the dynamics of a trapped fermion gas
We present a theoretical study of the dynamical behavior of a gas made of
ultracold fermionic atoms, which during their motions can collide with a much
smaller number of thermal bosonic impurities. The atoms are confined inside
harmonic traps and the interactions between the two species are treated as due
to s-wave scattering with a negative scattering length modeling the 40K-87Rb
fermion-boson system. We set the fermions into motion by giving a small shift
to their trap center and examine two alternative types of initial conditions,
referring to (i) a close-to-equilibrium situation in which the two species are
at the same temperature (well below the Fermi temperature and well above the
Bose-Einstein condensation temperature); and (ii) a far-from-equilibrium case
in which the impurities are given a Boltzmann distribution of momenta while the
fermions are at very low temperatures. The dynamics of the gas is evaluated by
the numerical solution of the Vlasov-Landau equations for the one-body
distribution functions, supported by some analytical results on the collisional
properties of a fermion gas. We find that the trapped gaseous mixture is close
to the collisionless regime for values of the parameters corresponding to
current experiments, but can be driven towards a collisional regime even
without increasing the strength of the interactions, either by going over to
heavier impurity masses or by matching the width of the momentum distribution
of the impurities to the Fermi momentum of the fermion gas.Comment: 7 pages, 4 figures, RevTeX 4, accepted in PR
Ultra-bright omni-directional collective emission of correlated photon pairs from atomic vapors
Spontaneous four-wave mixing can generate highly correlated photon pairs from
atomic vapors. We show that multi-photon pumping of dipole-forbidden
transitions in a recoil-free geometry can result in ultra-bright pair-emission
in the full 4\pi solid angle, while strongly suppresses background Rayleigh
scattering and associated atomic heating, Such a system can produce photon
pairs at rates of ~ 10 ^12 per second, given only moderate optical depths of 10
~ 100, or alternatively, the system can generate paired photons with
sub-natural bandwidths at lower production rates. We derive a rate-equation
based theory of the collective atomic population and coherence dynamics, and
present numerical simulations for a toy model, as well as realistic model
systems based on 133 Cs and 171 Yb level structures. Lastly, we demonstrate
that dark-state adiabatic following (EIT) and/or timescale hierarchy protects
the paired photons from reabsorption as they propagate through an optically
thick sample
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