25,085 research outputs found
Bright bichromatic entanglement and quantum dynamics of sum frequency generation
We investigate the quantum properties of the well-known process of sum
frequency generation, showing that it is potentially a very useful source of
non-classical states of the electromagnetic field, some of which are not
possible with the more common techniques. We show that it can produce
quadrature squeezed light, bright bichromatic entangled states and symmetric
and asymmetric demonstrations of the Einstein-Podolsky-Rosen paradox. We also
show that the semiclassical equations totally fail to describe the mean-field
dynamics when the cavity is strongly pumped
Quantum ultra-cold atomtronics
It is known that a semi-classical analysis is not always adequate for
atomtronics devices, but that a fully quantum analysis is often necessary to
make reliable predictions. While small numbers of atoms at a small number of
sites are tractable using the density matrix, a fully quantum analysis is often
not straightforward as the system becomes larger. We show that the fully
quantum positive-P representation is then a viable calculational tool. We
postulate an atomtronic phase-gate consisting of four wells in a Bose-Hubbard
configuration, for which the semi-classical dynamics are controllable using the
phase of the atomic mode in one of the wells. We show that the quantum
predictions of the positive-P representation for the performance of this device
have little relation to those found semi-classically, and that the performance
depends markedly on the actual quantum states of the initially occupied modes.
We find that initial coherent states lead to closest to classical dynamics, but
that initial Fock states give results that are quite different. A fully quantum
analysis also opens the door for deeply quantum atomtronics, in which
properties such as entanglement and EPR (Einstein-Podolsky-Rosen) steering
become valuable technical properties of a device.Comment: 12 pages, 6 figures, submitted to Phys. Rev
A quantum correlated twin atom laser from a Bose-Hubbard system
We propose and evaluate a method to construct a quantum correlated twin atom
laser using a pumped and damped Bose-Hubbard inline trimer which can operate in
a stationary regime. With pumping via a source condensate filling the middle
well and damping using either an electron beam or optical means at the two end
wells, we show that bipartite quantum correlations build up between the ends of
the chain, and that these can be measured either in situ or in the outcoupled
beams. While nothing similar to our system has yet been achieved
experimentally, recent advances mean that it should be practically realisable
in the near future.Comment: 15 pages, 8 figures, theory. Typos fixed and material added to
introductio
Multiquark Hadrons
A number of candidate multiquark hadrons, i.e., particle resonances with
substructures that are more complex than the quark-antiquark mesons and
three-quark baryons that are prescribed in the textbooks, have recently been
observed. In this talk I present: some recent preliminary BESIII results on the
near-threshold behavior of sigma(e+e- --> Lambda Lambda-bar) that may or may
not be related to multiquark mesons in the light- and strange-quark sectors;
results from Belle and LHCb on the electrically charged, charmoniumlike
Z(4430)^+ --> pi^+ psi ' resonance that necessarily has a four-quark
substructure; and the recent LHCb discovery of the P_c(4380) and P_c(4450)
hidden-charm resonances seen as a complex structure in the J/psi p invariant
mass distribution for Lambda_b --> K^-J/psi p decays and necessarily have a
five-quark substructure and are, therefore, prominent candidates for pentaquark
baryons.Comment: 12 pages, 9 figures, summary of a talk presented at the 12th
Conference on Hypernuclear and Strange Particle Physics (HYP2015), September
7-12, 2015 Sendai, JAPAN. To appear in the JPS Conference proceeding
Phase-space analysis of bosonic spontaneous emission
We present phase-space techniques for the modelling of spontaneous emission
in two-level bosonic atoms. The positive-P representation is shown to give a
full and complete description and can be further developed to give exact
treatments of the interaction of degenerate bosons with the electromagnetic
field in a given experimental situation. The Wigner representation, even when
truncated at second order, is shown to need a doubling of the phase-space to
allow for a positive-definite diffusion matrix in the appropriate Fokker-Planck
equation and still fails to agree with the full quantum results of the
positive-P representation. We show that quantum statistics and correlations
between the ground and excited states affect the dynamics of the emission
process, so that it is in general non-exponential.Comment: 16 pages, 6 figure
Mesoscopic dynamical differences from quantum state preparation in a Bose-Hubbard trimer
Conventional wisdom is that quantum effects will tend to disappear as the
number of quanta in a system increases, and the evolution of a system will
become closer to that described by mean field classical equations. In this
letter we combine newly developed experimental techniques to propose and
analyse an experiment using a Bose-Hubbard trimer where the opposite is the
case. We find that differences in the preparation of a centrally evacuated
trimer can lead to readily observable differences in the subsequent dynamics
which increase with system size. Importantly, these differences can be detected
by the simple measurements of atomic number.Comment: 5 pages, 4 figures, theor
Tripartite entanglement from interlinked parametric interactions
We examine the tripartite entanglement properties of an optical system using
interlinked interactions, recently studied experimentally in terms
of its phase-matching properties by Bondani et al [M. Bondani, A. Allevi, E.
Gevinti, A. Agliati, and A. Andreoni, arXiv:quant-ph/0604002.]. We show that
the system does produce output modes which are genuinely tripartite entangled
and that detection of this entanglement depends crucially on the correlation
functions which are measured, with a three-mode Einstein-Podolsky-Rosen
inequality being the most sensitive.Comment: 15 pages, 5 figure
Asymmetric Gaussian steering: when Alice and Bob disagree
Asymmetric steering is an effect whereby an inseparable bipartite system can
be found to be described by either quantum mechanics or local hidden variable
theories depending on which one of Alice or Bob makes the required
measurements. We show that, even with an inseparable bipartite system,
situations can arise where Gaussian measurements on one half are not sufficient
to answer the fundamental question of which theory gives an adequate
description and the whole system must be considered. This phenomenon is
possible because of an asymmetry in the definition of the original
Einstein-Podolsky-Rosen paradox and in this article we show theoretically that
it may be demonstrated, at least in the case where Alice and Bob can only make
Gaussian measurements, using the intracavity nonlinear coupler.Comment: 5 Pages, 4 Figure
First principles structures and circular dichroism spectra for the close-packed and the 7/2 motif of collagen
The recently proposed close-packed motif for collagen is investigated using
first principles semi-empirical wave function theory and Kohn-Sham density
functional theory. Under these refinements the close-packed motif is shown to
be stable. For the case of the 7/2 motif a similar stability exists. The
electronic circular dichroism of the close-packed model has a significant
negative bias and a large signal. An interesting feature of the close-packed
structure is the existence of a central channel. Simulations show that, if
hydrogen atoms are placed in the cavity, a chain of molecular hydrogens is
formed suggesting a possible biological function for molecular hydrogen.Comment: 12 pages, 3 figures; 3(PPG)_6 xyz file attached; v2: minor
modification
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