6,824 research outputs found
Optimal Generation of Pulsed Entangled Photon Pairs
We experimentally investigate a double-pass parametric down-conversion scheme
for producing pulsed, polarization-entangled photon pairs with high visibility.
The amplitudes for creating photon pairs on each pass interfere to compensate
for distinguishing characteristics that normally degrade two-photon visibility.
The result is a high-flux source of polarization-entangled photon pulses that
does not require spectral filtering. We observe quantum interference visibility
of over 95% without the use of spectral filters for 200 femtosecond pulses, and
up to 98.1% with 5 nm bandwidth filters.Comment: 8 pages, 6 figure
Unified Superfluid Dark Sector
We present a novel theory of a unified dark sector, where late-time cosmic
acceleration emerges from the dark matter superfluid framework. The system is
described by a superfluid mixture consisting of two distinguishable states with
a small energy gap, such as the ground state and an excited state of dark
matter. Given their contact in the superfluid, interaction between those states
can happen, converting one state into the other. This long range interaction
within the superfluid couples the two superfluid phonon species through a
cosine potential motivated by Josephson/Rabi interactions. As a consequence of
this potential, a new dynamics of late-time accelerated expansion emerges in
this system, without the need of dark energy, coming from a universe containing
only this two-state DM superfluid. Because the superfluid species are
non-relativistic, their sound speeds remain suitably small throughout the
evolution. We calculate the expansion history and growth of linear
perturbations, and compare the results to CDM cosmology. For the
fiducial parameters studied here, the predicted expansion and growth function
are close to those of CDM, but the difference in the predicted growth
rate is significant at late times. The present theory nicely complements the
recent proposal of dark matter superfluidity to explain the empirical success
of MOdified Newtonian Dynamics (MOND) on galactic scales, thus offering a
unified framework for dark matter, dark energy, and MOND phenomenology.Comment: 27 pages, 4 figures. v2: Version accepted in JCA
Multiphoton path entanglement by non-local bunching
Multiphoton path entanglement is created without applying post-selection, by
manipulating the state of stimulated parametric down-conversion. A specific
measurement on one of the two output spatial modes leads to the non-local
bunching of the photons of the other mode, forming the desired multiphoton path
entangled state. We present experimental results for the case of a heralded
two-photon path entangled state and show how to extend this scheme to higher
photon numbers.Comment: 4 pages, 5 figures, published versio
Nonlinear Interferometry via Fock State Projection
We use a photon-number resolving detector to monitor the photon number
distribution of the output of an interferometer, as a function of phase delay.
As inputs we use coherent states with mean photon number up to seven. The
postselection of a specific Fock (photon-number) state effectively induces
high-order optical non-linearities. Following a scheme by Bentley and Boyd
[S.J. Bentley and R.W. Boyd, Optics Express 12, 5735 (2004)] we explore this
effect to demonstrate interference patterns a factor of five smaller than the
Rayleigh limit.Comment: 4 pages, 5 figure
The four fixed points of scale invariant single field cosmological models
We introduce a new set of flow parameters to describe the time dependence of
the equation of state and the speed of sound in single field cosmological
models. A scale invariant power spectrum is produced if these flow parameters
satisfy specific dynamical equations. We analyze the flow of these parameters
and find four types of fixed points that encompass all known single field
models. Moreover, near each fixed point we uncover new models where the scale
invariance of the power spectrum relies on having simultaneously time varying
speed of sound and equation of state. We describe several distinctive new
models and discuss constraints from strong coupling and superluminality.Comment: 24 pages, 6 figure
Phase detection at the quantum limit with multi-photon Mach-Zehnder interferometry
We study a Mach-Zehnder interferometer fed by a coherent state in one input
port and vacuum in the other. We explore a Bayesian phase estimation strategy
to demonstrate that it is possible to achieve the standard quantum limit
independently from the true value of the phase shift and specific assumptions
on the noise of the interferometer. We have been able to implement the protocol
using parallel operation of two photon-number-resolving detectors and
multiphoton coincidence logic electronics at the output ports of a
weakly-illuminated Mach-Zehnder interferometer. This protocol is unbiased and
saturates the Cramer-Rao phase uncertainty bound and, therefore, is an optimal
phase estimation strategy.Comment: 4 pages, 5 figures replaced fig. 1 to correct graphics bu
PUK20 Prioritization of Comparative Effectiveness Research Questions Based On Identification of The Most Relevant Outcomes To Improve Clinical Practice: An Application of Mcda To Dialysis Research Planning
Quantum Fields in a Big Crunch/Big Bang Spacetime
We consider quantum field theory on a spacetime representing the Big
Crunch/Big Bang transition postulated in the ekpyrotic or cyclic cosmologies.
We show via several independent methods that an essentially unique matching
rule holds connecting the incoming state, in which a single extra dimension
shrinks to zero, to the outgoing state in which it re-expands at the same rate.
For free fields in our construction there is no particle production from the
incoming adiabatic vacuum. When interactions are included the total particle
production for fixed external momentum is finite at tree level. We discuss a
formal correspondence between our construction and quantum field theory on de
Sitter spacetime.Comment: 30 pages, RevTex file, five postscript figure file
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