1,300 research outputs found
On-chip III-V monolithic integration of heralded single photon sources and beamsplitters
We demonstrate a monolithic III-V photonic circuit combining a heralded
single photon source with a beamsplitter, at room temperature and telecom
wavelength. Pulsed parametric down-conversion in an AlGaAs waveguide generates
counterpropagating photons, one of which is used to herald the injection of its
twin into the beamsplitter. We use this configuration to implement an
integrated Hanbury-Brown and Twiss experiment, yielding a heralded second-order
correlation that confirms single-photon
operation. The demonstrated generation and manipulation of quantum states on a
single III-V semiconductor chip opens promising avenues towards real-world
applications in quantum information
A 1.3 cm Line Survey toward Orion KL
Orion KL has served as a benchmark for spectral line searches throughout the
(sub)millimeter regime. The main goal is to systematically study spectral
characteristics of Orion KL in the 1.3 cm band. We carried out a spectral line
survey (17.9 GHz to 26.2 GHz) with the Effelsberg-100 m telescope towards Orion
KL. We find 261 spectral lines, yielding an average line density of about 32
spectral features per GHz above 3. The identified lines include 164
radio recombination lines (RRLs) and 97 molecular lines. A total of 23
molecular transitions from species known to exist in Orion KL are detected for
the first time in the interstellar medium. Non-metastable 15NH3 transitions are
detected in Orion KL for the first time. Based on the velocity information of
detected lines and the ALMA images, the spatial origins of molecular emission
are constrained and discussed. A narrow feature is found in SO2
(), possibly suggesting the presence of a maser line. Column
densities and fractional abundances relative to H2 are estimated for 12
molecules with LTE methods. Rotational diagrams of non-metastable 14NH3
transitions with J=K+1 to J=K+4 yield different results; metastable 15NH3 is
found to have a higher excitation temperature than non-metastable 15NH3,
indicating that they may trace different regions. Elemental and isotopic
abundance ratios are estimated: 12C/13C=63+-17, 14N/15N=100+-51,
D/H=0.0083+-0.0045. The dispersion of the He/H ratios derived from
H/He pairs to H/He pairs is very small, which
is consistent with theoretical predictions that the departure coefficients bn
factors for hydrogen and helium are nearly identical. Based on a non-LTE code
neglecting excitation by the infrared radiation field and a likelihood
analysis, we find that the denser regions have lower kinetic temperature, which
favors an external heating of the Hot Core.Comment: 70 pages, 26 figures, 12 tables, accepted for publication in A&A.
Figs. 1, 2, 8, 9 have been downsize
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
Simplified Quantum Process Tomography
We propose and evaluate experimentally an approach to quantum process
tomography that completely removes the scaling problem plaguing the standard
approach. The key to this simplification is the incorporation of prior
knowledge of the class of physical interactions involved in generating the
dynamics, which reduces the problem to one of parameter estimation. This allows
part of the problem to be tackled using efficient convex methods, which, when
coupled with a constraint on some parameters allows globally optimal estimates
for the Kraus operators to be determined from experimental data. Parameterising
the maps provides further advantages: it allows the incorporation of mixed
states of the environment as well as some initial correlation between the
system and environment, both of which are common physical situations following
excitation of the system away from thermal equilibrium. Although the approach
is not universal, in cases where it is valid it returns a complete set of
positive maps for the dynamical evolution of a quantum system at all times.Comment: Added references to interesting related work by Bendersky et a
Detector-Agnostic Phase-Space Distributions
The representation of quantum states via phase-space functions constitutes an
intuitive technique to characterize light. However, the reconstruction of such
distributions is challenging as it demands specific types of detectors and
detailed models thereof to account for their particular properties and
imperfections. To overcome these obstacles, we derive and implement a
measurement scheme that enables a reconstruction of phase-space distributions
for arbitrary states whose functionality does not depend on the knowledge of
the detectors, thus defining the notion of detector-agnostic phase-space
distributions. Our theory presents a generalization of well-known phase-space
quasiprobability distributions, such as the Wigner function. We implement our
measurement protocol, using state-of-the-art transition-edge sensors without
performing a detector characterization. Based on our approach, we reveal the
characteristic features of heralded single- and two-photon states in phase
space and certify their nonclassicality with high statistical significance
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
ATLASGAL - towards a complete sample of massive star forming clumps
By matching infrared-selected, massive young stellar objects (MYSOs) and compact HII regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ~1000 embedded young massive stars between 280{ring operator} <lPeer reviewedFinal Accepted Versio
Interfacing GHz-bandwidth heralded single photons with a room-temperature Raman quantum memory
Photonics is a promising platform for quantum technologies. However, photon
sources and two-photon gates currently only operate probabilistically.
Large-scale photonic processing will therefore be impossible without a
multiplexing strategy to actively select successful events. High
time-bandwidth-product quantum memories - devices that store and retrieve
single photons on-demand - provide an efficient remedy via active
synchronisation. Here we interface a GHz-bandwidth heralded single-photon
source and a room-temperature Raman memory with a time-bandwidth product
exceeding 1000. We store heralded single photons and observe a clear influence
of the input photon statistics on the retrieved light, which agrees with our
theoretical model. The preservation of the stored field's statistics is limited
by four-wave-mixing noise, which we identify as the key remaining challenge in
the development of practical memories for scalable photonic information
processing
NH_3(1_0-0_0) in the pre-stellar core L1544
Pre-stellar cores represent the initial conditions in the process of star and
planet formation, therefore it is important to study their physical and
chemical structure. Because of their volatility, nitrogen-bearing molecules are
key to study the dense and cold gas present in pre-stellar cores. The NH_3
rotational transition detected with Herschel-HIFI provides a unique combination
of sensitivity and spectral resolution to further investigate physical and
chemical processes in pre-stellar cores. Here we present the velocity-resolved
Herschel-HIFI observations of the ortho-NH_3(1_0-0_0) line at 572 GHz and study
the abundance profile of ammonia across the pre-stellar core L1544 to test
current theories of its physical and chemical structure.
Recently calculated collisional coefficients have been included in our
non-LTE radiative transfer code to reproduce Herschel observations. A gas-grain
chemical model, including spin-state chemistry and applied to the (static)
physical structure of L1544 is also used to infer the abundance profile of
ortho-NH_3 . The hyperfine structure of ortho-NH_3(1_0-0_0) is resolved for the
first time in space. All the hyperfine components are strongly self-absorbed.
The profile can be reproduced if the core is contracting in quasi-equilibrium,
consistent with previous work, and if the NH_3 abundance is slightly rising
toward the core centre, as deduced from previous interferometric observations
of para-NH_3(1,1). The chemical model overestimates the NH_3 abundance at radii
between ~ 4000 and 15000 AU by about two orders of magnitude and underestimates
the abundance toward the core centre by more than one order of magnitude. Our
observations show that chemical models applied to static clouds have problems
in reproducing NH_3 observations.Comment: accepted for publication in A&A Letter
Nature of two massive protostellar candidates: IRAs 21307+5049 and IRAS 22172+5549
We present observations of continuum and molecular lines towards the
protostar candidates IRAS 21307+5049 and IRAS 22172+5549. Single-dish maps in
the 12CO(2--1), C18O(2--1), HCO+(1--0) lines and sub-mm continuum are compared
with interferometric maps in the 12CO(1--0) line and 3 mm continuum, and with
mid- and near-infrared images. A plausible interpretation of our data based on
the continuum maps and spectral energy distributions is that two components are
present: a compact molecular core, responsible for the continuum emission at
wavelengths longer than ~25 \mum, and a cluster of stars located close to the
center of the core, but not spatially coincident with it, responsible for the
emission at shorter wavelengths. The core is approximately located at the
center of the associated molecular outflow, detected for both sources in the
12CO(1--0) and (2--1) lines. The cores have masses of ~50 M_{\odot}, and
luminosities of ~10^{3} L_{\odot}. The outflows parameters are consistent with
those typically found in high-mass young stellar objects. Our results support
the hypothesis that in these sources the luminosity is dominated by accretion
rather than by nuclear burning. We conclude that the sources embedded inside
the cores are likely protostars with mass ~5-8 M_{\odot}.Comment: 19 pages, 17 figure
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