1,182 research outputs found
Benchmarking of Gaussian boson sampling using two-point correlators
Gaussian boson sampling is a promising scheme for demonstrating a quantum
computational advantage using photonic states that are accessible in a
laboratory and, thus, offer scalable sources of quantum light. In this
contribution, we study two-point photon-number correlation functions to gain
insight into the interference of Gaussian states in optical networks. We
investigate the characteristic features of statistical signatures which enable
us to distinguish classical from quantum interference. In contrast to the
typical implementation of boson sampling, we find additional contributions to
the correlators under study which stem from the phase dependence of Gaussian
states and which are not observable when Fock states interfere. Using the first
three moments, we formulate the tools required to experimentally observe
signatures of quantum interference of Gaussian states using two outputs only.
By considering the current architectural limitations in realistic experiments,
we further show that a statistically significant discrimination between quantum
and classical interference is possible even in the presence of loss, noise, and
a finite photon-number resolution. Therefore, we formulate and apply a
theoretical framework to benchmark the quantum features of Gaussian boson
sampling under realistic conditions
Dissipation of Quasiclassical Turbulence in Superfluid He
We compare the decay of turbulence in superfluid He produced by a moving
grid to the decay of turbulence created by either impulsive spin-down to rest
or by intense ion injection. In all cases the vortex line density decays at
late time as . At temperatures above 0.8 K, all methods
result in the same rate of decay. Below 0.8 K, the spin-down turbulence
maintains initial rotation and decays slower than grid turbulence and ion-jet
turbulence. This may be due to a decoupling of the large-scale superfluid flow
from the normal component at low temperatures, which changes its effective
boundary condition from no-slip to slip.Comment: Main article: 5 pages, 3 figures. Supplemental material: 4 pages, 3
figures. Accepted for publication in Physical Review Letter
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
A ferrofluid based neural network: design of an analogue associative memory
We analyse an associative memory based on a ferrofluid, consisting of a
system of magnetic nano-particles suspended in a carrier fluid of variable
viscosity subject to patterns of magnetic fields from an array of input and
output magnetic pads. The association relies on forming patterns in the
ferrofluid during a trainingdphase, in which the magnetic dipoles are free to
move and rotate to minimize the total energy of the system. Once equilibrated
in energy for a given input-output magnetic field pattern-pair the particles
are fully or partially immobilized by cooling the carrier liquid. Thus produced
particle distributions control the memory states, which are read out
magnetically using spin-valve sensors incorporated in the output pads. The
actual memory consists of spin distributions that is dynamic in nature,
realized only in response to the input patterns that the system has been
trained for. Two training algorithms for storing multiple patterns are
investigated. Using Monte Carlo simulations of the physical system we
demonstrate that the device is capable of storing and recalling two sets of
images, each with an accuracy approaching 100%.Comment: submitted to Neural Network
Dense Ionized and Neutral Gas Surrounding Sgr A*
We present high resolution H41a hydrogen recombination line observations of
the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter
Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s.
New observations of H31a, H35a, H41a, and H44a lines were obtained using the
NRAO 12-m telescope, and their relative line strengths are interpreted in terms
of various emission mechanisms. These are the most extensive and most sensitive
observations of recombination line to date. Observations of HCO+ (1 - 0)
transition at 89 GHz are also obtained simultaneously with a 40% improved
angular resolution and 4-15 times improved sensitivity over previous
observations, and the distribution and kinematics of the dense molecular gas in
the circumnuclear disk (CND) are mapped and compared with those of the ionized
gas. The line brightness ratios of the hydrogen recombination lines are
consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000
cm near LTE condition. A virial analysis suggests that the most
prominent molecular gas clumps in the CND have mean densities of 10^7 cm^{-3},
sufficient to withstand the tidal shear in the Galactic Center region.
Therefore, these clumps may survive over several dynamical times, and the CND
may be a dynamically stable structure. We estimate a total gas mass of 3 x 10^5
solar mass for the CND. \Comment: 34 pages including 11 figures (4 jpgs), Latex, uses aastex. The full
pdf format file including high resolution figures is available at
http://www.astro.umass.edu/~myun/papers/SgrA.pdf . To appear in the 20
November 2004 (V616) issue of the Astrophysical Journa
A necklace of dense cores in the high-mass star forming region G35.20-0.74N: ALMA observations
The present study aims at characterizing the massive star forming region
G35.20N, which is found associated with at least one massive outflow and
contains multiple dense cores, one of them recently found associated with a
Keplerian rotating disk. We used ALMA to observe the G35.20N region in the
continuum and line emission at 350 GHz. The observed frequency range covers
tracers of dense gas (e.g. H13CO+, C17O), molecular outflows (e.g. SiO), and
hot cores (e.g. CH3CN, CH3OH). The ALMA 870 um continuum emission map reveals
an elongated dust structure (0.15 pc long and 0.013 pc wide) perpendicular to
the large-scale molecular outflow detected in the region, and fragmented into a
number of cores with masses 1-10 Msun and sizes 1600 AU. The cores appear
regularly spaced with a separation of 0.023 pc. The emission of dense gas
tracers such as H13CO+ or C17O is extended and coincident with the dust
elongated structure. The three strongest dust cores show emission of complex
organic molecules characteristic of hot cores, with temperatures around 200 K,
and relative abundances 0.2-2x10^(-8) for CH3CN and 0.6-5x10^(-6) for CH3OH.
The two cores with highest mass (cores A and B) show coherent velocity fields,
with gradients almost aligned with the dust elongated structure. Those velocity
gradients are consistent with Keplerian disks rotating about central masses of
4-18 Msun. Perpendicular to the velocity gradients we have identified a
large-scale precessing jet/outflow associated with core B, and hints of an
east-west jet/outflow associated with core A. The elongated dust structure in
G35.20N is fragmented into a number of dense cores that may form massive stars.
Based on the velocity field of the dense gas, the orientation of the magnetic
field, and the regularly spaced fragmentation, we interpret this elongated
structure as the densest part of a 1D filament fragmenting and forming massive
stars.Comment: 24 pages, 26 figures, accepted for publication in Astronomy and
Astrophysics (abstract modified to fit arXiv restrictions
A Multi-Wavelength High Resolution Study of the S255 Star Forming Region. General structure and kinematics
We present observational data for two main components (S255IR and S255N) of
the S255 high mass star forming region in continuum and molecular lines
obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23
and 50 cm with the GMRT. The angular resolution was from ~ 2" to ~ 5" for all
instruments. With the SMA we detected a total of about 50 spectral lines of 20
different molecules (including isotopologues). About half of the lines and half
of the species (in particular N2H+, SiO, C34S, DCN, DNC, DCO+, HC3N, H2CO,
H2CS, SO2) have not been previously reported in S255IR and partly in S255N at
high angular resolution. Our data reveal several new clumps in the S255IR and
S255N areas by their millimeter wave continuum emission. Masses of these clumps
are estimated at a few solar masses. The line widths greatly exceed expected
thermal widths. These clumps have practically no association with NIR or radio
continuum sources, implying a very early stage of evolution. At the same time,
our SiO data indicate the presence of high-velocity outflows related to some of
these clumps. In some cases, strong molecular emission at velocities of the
quiescent gas has no detectable counterpart in the continuum. We discuss the
main features of the distribution of NH3, N2H+, and deuterated molecules. We
estimate properties of decimeter wave radio continuum sources and their
relationship with the molecular material.Comment: 21 pages, 26 figures, accepted for publication in Astrophysical
Journa
The challenges of developing rainfall intensity-duration-frequency curves and national flood hazard maps for the Caribbean
In many Caribbean countries a lack of established good practice methods means that engineers and planners are often unable to plan for and mitigate floods effectively. In most Caribbean states rainfall intensity – duration – frequency (IDF) curves are not readily available. This is a result of the limited quantity of short duration rainfall data available and also because the few IDF curves that have been developed in the region are generally not in the public domain. The lack of readily available IDF curves in the region often results in engineers responsible for the design of key infrastructure inappropriately “transferring” IDF curves developed for islands, where rainfall is less intense, for use in their designs. There are no countries in the Caribbean with nationally consistent flood hazard maps. This often leaves spatial and emergency planners with insufficient information to make important strategic decisions. This paper details the challenges that were faced in producing rainfall IDF curves for return periods up to 1 in 50 years and nationally consistent extreme fluvial flood extent maps with limited data for selected countries within the Caribbean. Recommendations are made for the future development of rainfall IDF curves and national flood maps in the region both in terms of data and organisational requirements
Avalanche Photo-Detection for High Data Rate Applications
Avalanche photo detection is commonly used in applications which require
single photon sensitivity. We examine the limits of using avalanche photo
diodes (APD) for characterising photon statistics at high data rates. To
identify the regime of linear APD operation we employ a ps-pulsed diode laser
with variable repetition rates between 0.5MHz and 80MHz. We modify the mean
optical power of the coherent pulses by applying different levels of
well-calibrated attenuation. The linearity at high repetition rates is limited
by the APD dead time and a non-linear response arises at higher photon-numbers
due to multiphoton events. Assuming Poissonian input light statistics we
ascertain the effective mean photon-number of the incident light with high
accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number
resolution by photon chopping. This detection setup extends the linear response
function to higher photon-numbers and statistical methods may be used to
compensate for non-linearity. We investigated this effect, compare it to the
single APD case and show the validity of the convolution treatment in the TMD
data analysis.Comment: 16 pages, 5 figure
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