3,978 research outputs found
Bogoliubov theory of entanglement in a Bose-Einstein condensate
We consider a Bose-Einstein condensate which is illuminated by a short
resonant light pulse that coherently couples two internal states of the atoms.
We show that the subsequent time evolution prepares the atoms in an interesting
entangled state called a spin squeezed state. This evolution is analysed in
detail by developing a Bogoliubov theory which describes the entanglement of
the atoms. Our calculation is a consistent expansion in , where
is the number of particles in the condensate, and our theory predict that it is
possible to produce spin squeezing by at least a factor of . Within
the Bogoliubov approximation this result is independent of temperature.Comment: 14 pages, including 5 figures, minor changes in the presentatio
Structure of boson systems beyond the mean-field
We investigate systems of identical bosons with the focus on two-body
correlations. We use the hyperspherical adiabatic method and a decomposition of
the wave function in two-body amplitudes. An analytic parametrization is used
for the adiabatic effective radial potential. We discuss the structure of a
condensate for arbitrary scattering length. Stability and time scales for
various decay processes are estimated. The previously predicted Efimov-like
states are found to be very narrow. We discuss the validity conditions and
formal connections between the zero- and finite-range mean-field
approximations, Faddeev-Yakubovskii formulation, Jastrow ansatz, and the
present method. We compare numerical results from present work with mean-field
calculations and discuss qualitatively the connection with measurements.Comment: 26 pages, 6 figures, submitted to J. Phys. B. Ver. 2 is 28 pages with
modified figures and discussion
Biogas production by co-ensiling catch crops and straw, effect of substrate blend and microbial communities
The combination of catch crop (CC) and barley straw(S) for biogas production was investigated in order to evaluate the ensiling process in batch assay and in continuous process. Based on two new agriculture strategies designed to produce energy and improve nutrient cycling in organic farming are being evaluated, one of them consisting on the harvest of straw and catch crop in different periods whereas the other strategy consists on harvesting them at the same time. Catch crops is promoted to reduce nutrient leaching during rainy season and straw that is not used for animal feeding or bedding is generally left in the field. Mixtures of CC and S provides several advantages: 1) Provides adequate TS for silage, 2) Absorbs the silage effluent, 3) Produces high LAB activity, and 4) Provides an optimal C/N for anaerobic digestion (AD). The effect of feeding compositions (straw or manurea ddition) on the microbial community structures were also investigated
Experimentally obtaining the Likeness of Two Unknown Quantum States on an NMR Quantum Information Processor
Recently quantum states discrimination has been frequently studied. In this
paper we study them from the other way round, the likeness of two quantum
states. The fidelity is used to describe the likeness of two quantum states.
Then we presented a scheme to obtain the fidelity of two unknown qubits
directly from the integral area of the spectra of the assistant qubit(spin) on
an NMR Quantum Information Processor. Finally we demonstrated the scheme on a
three-qubit quantum information processor. The experimental data are consistent
with the theoretical expectation with an average error of 0.05, which confirms
the scheme.Comment: 3 pages, 4 figure
Entanglement and Extreme Spin Squeezing
For any mean value of a cartesian component of a spin vector we identify the
smallest possible uncertainty in any of the orthogonal components. The
corresponding states are optimal for spectroscopy and atomic clocks. We show
that the results for different spin J can be used to identify entanglement and
to quantity the depth of entanglement in systems with many particles. With the
procedure developed in this letter, collective spin measurements on an ensemble
of particles can be used as an experimental proof of multi-particle
entanglementComment: 4 pages, 2 figures, minor changes in the presentatio
Spin-spin interaction and spin-squeezing in an optical lattice
We show that by displacing two optical lattices with respect to each other,
we may produce interactions similar to the ones describing ferro-magnetism in
condensed matter physics. We also show that particularly simple choices of the
interaction lead to spin-squeezing, which may be used to improve the
sensitivity of atomic clocks. Spin-squeezing is generated even with partially,
and randomly, filled lattices, and our proposal may be implemented with current
technology.Comment: 4 pages, including 4 figure
Local Simulation Algorithms for Coulombic Interactions
We consider dynamically constrained Monte-Carlo dynamics and show that this
leads to the generation of long ranged effective interactions. This allows us
to construct a local algorithm for the simulation of charged systems without
ever having to evaluate pair potentials or solve the Poisson equation. We
discuss a simple implementation of a charged lattice gas as well as more
elaborate off-lattice versions of the algorithm. There are analogies between
our formulation of electrostatics and the bosonic Hubbard model in the phase
approximation. Cluster methods developed for this model further improve the
efficiency of the electrostatics algorithm.Comment: Proceedings Statphys22 10 page
Characterizing the spin state of an atomic ensemble using the magneto-optical resonance method
Quantum information protocols utilizing atomic ensembles require preparation
of a coherent spin state (CSS) of the ensemble as an important starting point.
We investigate the magneto-optical resonance method for characterizing a spin
state of cesium atoms in a paraffin coated vapor cell. Atoms in a constant
magnetic field are subject to an off-resonant laser beam and an RF magnetic
field. The spectrum of the Zeeman sub-levels, in particular the weak quadratic
Zeeman effect, enables us to measure the spin orientation, the number of atoms,
and the transverse spin coherence time. Notably the use of 894nm pumping light
on the D1-line, ensuring the state F=4, m_F=4 to be a dark state, helps us to
achieve spin orientation of better than 98%. Hence we can establish a CSS with
high accuracy which is critical for the analysis of the entangled states of
atoms.Comment: 12 pages ReVTeX, 6 figures, in v2 added ref. and corrected typo
Magnetization profiles and NMR spectra of doped Haldane chains at finite temperatures
Open segments of S=1 antiferromagnetic spin chains are studied at finite
temperatures and fields using continuous time Quantum Monte Carlo techniques.
By calculating the resulting magnetization profiles for a large range of chain
lengths with fixed field and temperature we reconstruct the experimentally
measured NMR spectrum of impurity doped YBaNiMgO. For
temperatures above the gap the calculated NMR spectra are in excellent
agreement with the experimental results, confirming the existence of
excitations at the end of open S=1 chain segments. At temperatures below the
gap, neglecting inter chain couplings, we still find well defined peaks in the
calculated NMR spectra corresponding to the chain end excitations. At
low temperatures, inter chain couplings could be important, resulting in a more
complicated phase.Comment: 7 pages, 5 figures, minor correction
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