43,282 research outputs found
Controlled asymmetry of EPR steering with an injected non-degenerate optical parametric oscillator
We propose and analyse a nonlinear optical apparatus in which the direction
of asymmetric steering is controllable within the apparatus, rather than by
adding noise to measurements. Using a nondegenerate parametric oscillator with
an injected signal field, we show how the directionality and extent of the
steering can be readily controlled for output modes which can be up to one
octave apart. The two downconverted modes, which exhibit the greater violations
of the steering inequalities, can also be controlled to exhibit asymmetric
steering in some regimes.Comment: Theory, 4 pages, 5 figures. Revised version after expert, well
written and useful referee report
Quantum dynamics and entanglement in coherent transport of atomic population
In this work we look at the quantum dynamics of the process known as either
transport without transit (TWT), or coherent transfer of atomic population
(CTAP), of a Bose-Einstein condensate from one well of a lattice potential to
another, non-adjacent well, without macroscopic occupation of the well between
the two. This process has previously been analysed and in this work we extend
those analyses by considering the effects of quantum statistics on the dynamics
and entanglement properties of the condensate modes in the two relevant wells.
In order to do this, we go beyond the mean-field analysis of the
Gross-Pitaevskii type approach and utilise the phase-space stochastic methods
so well known in quantum optics. In particular, we use the exact positive-P
representation where it is suitable, and the approximate truncated WIgner
representation otherwise. We find strong agreement between the results of these
two methods, with the mean-field dynamics not depending on the initial quantum
states of the trapped condensate. We find that the entanglement properties do
depend strongly on the initial quantum states, with quantitatively different
results found for coherent and Fock states. Comparison of the two methods gives
us confidence that the truncated Wigner representation delivers accurate
results for this system and is thus a useful method as the collisional
nonlinearity increases and the positive-P results fail to converge.Comment: 11 pages, 4 figure
Entanglement properties of third harmonic generation via direct and cascaded parametric processes
We compare the bipartite entanglement and EPR-steering properties of the two
different schemes which produce third harmonic optical fields from an input
field at the fundamental frequency. The first scheme uses second harmonic
cascaded with sum-frequency generation while the second uses triply degenerate
four-wave mixing, also known as direct third harmonic generation. We examine
and compare the two schemes in both the travelling wave and intra-cavity
configurations. We find that both schemes produce continuous-variable bipartite
entanglement and EPR-steering. The direct scheme produces a greater degree of
EPR-steering while the cascaded scheme allows for greater flexibility in having
three available bipartitions.Comment: 20 pages, 9 figures, theor
Tripartite correlations over two octaves from cascaded harmonic generation
We analyse the output quantum tripartite correlations from an intracavity
nonlinear optical system which uses cascaded nonlinearities to produce both
second and fourth harmonic outputs from an input field at the fundamental
frequency. Using fully quantum equations of motion, we investigate two
parameter regimes and show that the system produces tripartite inseparability,
entanglement and EPR steering, with the detection of these depending on the
correlations being considered.Comment: 15 pages, 4 figures, theoretical.arXiv admin note: text overlap with
arXiv:1707.0253
Entanglement and asymmetric steering over two octaves of frequency difference with cascaded harmonic generation
We analyse a nonlinear optical system which uses cascaded nonlinearities to
produce both second and fourth harmonic outputs from an input field at the
fundamental frequency. Using fully quantum equations of motion, we show that
the system produces quadrature squeezed outputs which exhibit bipartite
entanglement, EPR-steering, and asymmetric steering across a two octave
frequency range.Comment: 5 pages, 7 figures, theor
Solving the kernel perfect problem by (simple) forbidden subdigraphs for digraphs in some families of generalized tournaments and generalized bipartite tournaments
A digraph such that every proper induced subdigraph has a kernel is said to
be \emph{kernel perfect} (KP for short) (\emph{critical kernel imperfect} (CKI
for short) resp.) if the digraph has a kernel (does not have a kernel resp.).
The unique CKI-tournament is and the unique
KP-tournaments are the transitive tournaments, however bipartite tournaments
are KP. In this paper we characterize the CKI- and KP-digraphs for the
following families of digraphs: locally in-/out-semicomplete, asymmetric
arc-locally in-/out-semicomplete, asymmetric -quasi-transitive and
asymmetric -anti-quasi-transitive -free and we state that the problem
of determining whether a digraph of one of these families is CKI is polynomial,
giving a solution to a problem closely related to the following conjecture
posted by Bang-Jensen in 1998: the kernel problem is polynomially solvable for
locally in-semicomplete digraphs.Comment: 13 pages and 5 figure
Quantum correlations across two octaves from combined up and down conversion
We propose and analyse a cascaded optical parametric system which involves
three interacting modes across two octaves of frequency difference. Our system,
combining degenerate optical parametric oscillation (OPO) with second harmonic
generation (SHG), promises to be a useful source of squeezed and entangled
light at three differing frequencies. We show how changes in damping rates and
the ratio of the two concurrent nonlinearities affect the quantum correlations
in the output fields. We analyse the threshold behaviour, showing how the
normal OPO threshold is changed by the addition of the SHG interactions. We
also find that the inclusion of the OPO interaction removes the self-pulsing
behaviour found in normal SHG. Finally, we show how the Einstein-Podolsky-Rosen
correlations can be controlled by the injection of a coherent seed field at the
lower frequency.Comment: 23 pages, 11 figures, theor
Finite size effects and equilibration in Bose-Hubbard chains with central well dephasing
We investigate Bose-Hubbard chains in a central depleted well configuration,
with dephasing in the middle well. We look at equilibration of populations,
pseudo-entropy, and entanglement measures. Using stochastic integration in the
truncated Wigner representation, we find that the initial quantum states of the
occupied wells has an influence on the subsequent dynamics, and that with more
than three wells, the chains do not reach a full equilibrium, with edge effects
becoming important, and the time to reach the steady state becoming longer. The
evolutions with and without phase diffusion are qualitatively different. We
find no convincing evidence of entanglement in the final states with phase
diffusion. Although at least one accepted measure indicates the presence of
mode entanglement, we are easily able to show that it can give ambiguous
predictions.Comment: 20 pages, 12 figures, theor
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