10,766 research outputs found
Introductory assessment of orbiting reflections for terrestrial power generation
The use of orbiting mirrors for providing energy to ground conversion stations to produce electrical power is shown to be a viable, cost effective and environmentally sound alternative to satellite solar power stations and conventional power sources. This is accomplished with the use of very light weight metal coated polymeric films as mirrors which, after deployment at 800 km, are placed in operational orbit and controlled by solar radiation pressure. Relations are developed showing the influence of a number of parameters (mirror altitude, orbit inclination, period, mirror size and number, and atmospheric effects) on the reflected insolation that may be received by a ground spot as a function of location. Some attractive alternative uses of the reflection are briefly discussed as a beneficial adjuncts to the system
Optimal fidelity of teleportation of coherent states and entanglement
We study the Braunstein-Kimble protocol for the continuous variable
teleportation of a coherent state. We determine lower and upper bounds for the
optimal fidelity of teleportation, maximized over all local Gaussian operations
for a given entanglement of the two-mode Gaussian state shared by the sender
(Alice) and the receiver (Bob). We also determine the optimal local
transformations at Alice and Bob sites and the corresponding maximum fidelity
when one restricts to local trace-preserving Gaussian completely positive maps.Comment: 10 pages, 2 figure
Recovery of continuous wave squeezing at low frequencies
We propose and demonstrate a system that produces squeezed vacuum using a
pair of optical parametric amplifiers. This scheme allows the production of
phase sidebands on the squeezed vacuum which facilitate phase locking in
downstream applications. We observe strong, stably locked, continuous wave
vacuum squeezing at frequencies as low as 220 kHz. We propose an alternative
resonator configuration to overcome low frequency squeezing degradation caused
by the optical parametric amplifiers.Comment: 9 pages, 4 figure
Evanescent single-molecule biosensing with quantum limited precision
Sensors that are able to detect and track single unlabelled biomolecules are
an important tool both to understand biomolecular dynamics and interactions at
nanoscale, and for medical diagnostics operating at their ultimate detection
limits. Recently, exceptional sensitivity has been achieved using the strongly
enhanced evanescent fields provided by optical microcavities and nano-sized
plasmonic resonators. However, at high field intensities photodamage to the
biological specimen becomes increasingly problematic. Here, we introduce an
optical nanofibre based evanescent biosensor that operates at the fundamental
precision limit introduced by quantisation of light. This allows a four
order-of-magnitude reduction in optical intensity whilst maintaining
state-of-the-art sensitivity. It enable quantum noise limited tracking of
single biomolecules as small as 3.5 nm, and surface-molecule interactions to be
monitored over extended periods. By achieving quantum noise limited precision,
our approach provides a pathway towards quantum-enhanced single-molecule
biosensors.Comment: 17 pages, 4 figures, supplementary informatio
Squeezed state purification with linear optics and feed forward
A scheme for optimal and deterministic linear optical purification of mixed
squeezed Gaussian states is proposed and experimentally demonstrated. The
scheme requires only linear optical elements and homodyne detectors, and allows
the balance between purification efficacy and squeezing degradation to be
controlled. One particular choice of parameters gave a ten-fold reduction of
the thermal noise with a corresponding squeezing degradation of only 11%. We
prove optimality of the protocol, and show that it can be used to enhance the
performance of quantum informational protocols such as dense coding and
entanglement generation.Comment: 4 pages, 3 figure
Biased EPR entanglement and its application to teleportation
We consider pure continuous variable entanglement with non-equal correlations
between orthogonal quadratures. We introduce a simple protocol which equates
these correlations and in the process transforms the entanglement onto a state
with the minimum allowed number of photons. As an example we show that our
protocol transforms, through unitary local operations, a single squeezed beam
split on a beam splitter into the same entanglement that is produced when two
squeezed beams are mixed orthogonally. We demonstrate that this technique can
in principle facilitate perfect teleportation utilising only one squeezed beam.Comment: 8 pages, 5 figure
An experimental investigation of criteria for continuous variable entanglement
We generate a pair of entangled beams from the interference of two amplitude
squeezed beams. The entanglement is quantified in terms of EPR-paradox [Reid88]
and inseparability [Duan00] criteria, with observed results of and , respectively. Both results clearly beat the standard quantum
limit of unity. We experimentally analyze the effect of decoherence on each
criterion and demonstrate qualitative differences. We also characterize the
number of required and excess photons present in the entangled beams and
provide contour plots of the efficacy of quantum information protocols in terms
of these variables.Comment: 4 pages, 5 figure
Teleportation of continuous variable polarisation states
This paper discusses methods for the optical teleportation of continuous
variable polarisation states. We show that using two pairs of entangled beams,
generated using four squeezed beams, perfect teleportation of optical
polarisation states can be performed. Restricting ourselves to 3 squeezed
beams, we demonstrate that polarisation state teleportation can still exceed
the classical limit. The 3-squeezer schemes involve either the use of quantum
non-demolition measurement or biased entanglement generated from a single
squeezed beam. We analyse the efficacies of these schemes in terms of fidelity,
signal transfer coefficients and quantum correlations
Non-linear optomechanical measurement of mechanical motion
Precision measurement of non-linear observables is an important goal in all
facets of quantum optics. This allows measurement-based non-classical state
preparation, which has been applied to great success in various physical
systems, and provides a route for quantum information processing with otherwise
linear interactions. In cavity optomechanics much progress has been made using
linear interactions and measurement, but observation of non-linear mechanical
degrees-of-freedom remains outstanding. Here we report the observation of
displacement-squared thermal motion of a micro-mechanical resonator by
exploiting the intrinsic non-linearity of the radiation pressure interaction.
Using this measurement we generate bimodal mechanical states of motion with
separations and feature sizes well below 100~pm. Future improvements to this
approach will allow the preparation of quantum superposition states, which can
be used to experimentally explore collapse models of the wavefunction and the
potential for mechanical-resonator-based quantum information and metrology
applications.Comment: 8 pages, 4 figures, extensive supplementary material available with
published versio
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