831 research outputs found
Mid-infrared quantum optics in silicon
Applied quantum optics stands to revolutionise many aspects of information
technology, provided performance can be maintained when scaled up. Silicon
quantum photonics satisfies the scaling requirements of miniaturisation and
manufacturability, but at 1.55 m it suffers from unacceptable linear and
nonlinear loss. Here we show that, by translating silicon quantum photonics to
the mid-infrared, a new quantum optics platform is created which can
simultaneously maximise manufacturability and miniaturisation, while minimising
loss. We demonstrate the necessary platform components: photon-pair generation,
single-photon detection, and high-visibility quantum interference, all at
wavelengths beyond 2 m. Across various regimes, we observe a maximum net
coincidence rate of 448 12 Hz, a coincidence-to-accidental ratio of 25.7
1.1, and, a net two photon quantum interference visibility of 0.993
0.017. Mid-infrared silicon quantum photonics will bring new quantum
applications within reach.Comment: 8 pages, 4 figures; revised figures, updated discussion in section 3,
typos corrected, added referenc
Witnessing eigenstates for quantum simulation of Hamiltonian spectra
The efficient calculation of Hamiltonian spectra, a problem often intractable
on classical machines, can find application in many fields, from physics to
chemistry. Here, we introduce the concept of an "eigenstate witness" and
through it provide a new quantum approach which combines variational methods
and phase estimation to approximate eigenvalues for both ground and excited
states. This protocol is experimentally verified on a programmable silicon
quantum photonic chip, a mass-manufacturable platform, which embeds entangled
state generation, arbitrary controlled-unitary operations, and projective
measurements. Both ground and excited states are experimentally found with
fidelities >99%, and their eigenvalues are estimated with 32-bits of precision.
We also investigate and discuss the scalability of the approach and study its
performance through numerical simulations of more complex Hamiltonians. This
result shows promising progress towards quantum chemistry on quantum computers.Comment: 9 pages, 4 figures, plus Supplementary Material [New version with
minor typos corrected.
X-ray emission from MP Muscae: an old classical T Tauri star
We study the properties of X-ray emitting plasma of MP Mus, an old classical
T Tauri star. We aim at checking whether an accretion process produces the
observed X-ray emission and at deriving the accretion parameters and the
characteristics of the shock-heated plasma. We compare the properties of MP Mus
with those of younger classical T Tauri stars to test whether age is related to
the properties of the X-ray emission plasma. XMM-Newton X-ray spectra allows us
to measure plasma temperatures, abundances, and electron density. In particular
the density of cool plasma probes whether X-ray emission is produced by plasma
heated in the accretion process. X-ray emission from MP Mus originates from
high density cool plasma but a hot flaring component is also present,
suggesting that both coronal magnetic activity and accretion contribute to the
observed X-ray emission. We find a Ne/O ratio similar to that observed in the
much younger classical T Tauri star BP Tau. From the soft part of the X-ray
emission, mostly produced by plasma heated in the accretion shock, we derive a
mass accretion rate of 5x10^{-11} M_{sun} yr^{-1}.Comment: 4 pages, 4 postscript figures, accepted for publication as a Letter
in Astronomy and Astrophysic
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Coronagraphic imaging with the Near Infrared Camera and Multi Object
Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'')
radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected
light image at 1.1 micron shows the disk oriented at a position angle of 356
+/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic
scattering function of the dust in the disk makes the side inclined toward us,
the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from
the star and falls off to both larger and smaller radii. A region of depleted
material, or a gap, in the disk is centered 250 AU from the star. The dynamical
effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript
figures, Accepted to ApJ Letter
Resummation of the Divergent Perturbation Series for a Hydrogen Atom in an Electric Field
We consider the resummation of the perturbation series describing the energy
displacement of a hydrogenic bound state in an electric field (known as the
Stark effect or the LoSurdo-Stark effect), which constitutes a divergent formal
power series in the electric field strength. The perturbation series exhibits a
rich singularity structure in the Borel plane. Resummation methods are
presented which appear to lead to consistent results even in problematic cases
where isolated singularities or branch cuts are present on the positive and
negative real axis in the Borel plane. Two resummation prescriptions are
compared: (i) a variant of the Borel-Pade resummation method, with an
additional improvement due to utilization of the leading renormalon poles (for
a comprehensive discussion of renormalons see [M. Beneke, Phys. Rep. vol. 317,
p. 1 (1999)]), and (ii) a contour-improved combination of the Borel method with
an analytic continuation by conformal mapping, and Pade approximations in the
conformal variable. The singularity structure in the case of the LoSurdo-Stark
effect in the complex Borel plane is shown to be similar to (divergent)
perturbative expansions in quantum chromodynamics.Comment: 14 pages, RevTeX, 3 tables, 1 figure; numerical accuracy of results
enhanced; one section and one appendix added and some minor changes and
additions; to appear in phys. rev.
NICMOS Coronagraphic Observations of 55 Cancri
We present new near-infrared (1.1-micron) observations of the circumstellar
environment of the planet-bearing star 55 Cancri. With these Hubble Space
Telescope images we are unable to confirm the observation of bright scattered
radiation at longer NIR wavelengths previously reported by Trilling & Brown
(1998), and Trilling, Brown & Rivkin (2000). NICMOS coronagraphic images with
detection sensitivities to ~ 100 microJy arcsec at 1.1 microns in the
region 28 - 60 AU from the star fail to reveal any significant excess flux in
point- spread-function (PSF) subtracted images taken in two Hubble Space
Telescope orbits. These new observations place flux densities in the 19-28 AU
zone at a factor of ten or more below the reported ground-based observations.
Applying a suite of a dozen well-matched coronagraphic reference PSFs,
including one obtained in the same orbits as the observations of 55 Cnc,
yielded consistently null results in detecting a disk. We also searched for,
and failed to find, a suggested flux-excess anisotropy in the ratio of ~1.7:1
in the circumstellar background along and orthogonal to the plane of the
putative disk. We suggest that, if such a disk does exist, then the total
1.1-micron spectral flux density in an annular zone 28 - 42 AU from the star
must be no more than ~0.4mJy, at least ten times smaller than suggested by
Trilling and Brown, upon which their very large estimate for the total dust
mass (0.4~M_{\earth}) was based. Based on the far infrared and submillimeter
flux of this system and observations of scattered light and thermal emission
from other debris disks, we also expect the intensity of the scattered light to
be at least an order of magnitude below our upper limits.Comment: 40 pages, accepted to AJ 03OCT2000; 7 figures available at:
http://nicmosis.as.arizona.edu:8000/PREPRINTS/55CNC/55_CNC_PREPRINT.htm
Discovery of an 86 AU Radius Debris Ring Around HD 181327
HST/NICMOS PSF-subtracted coronagraphic observations of HD 181327 have
revealed the presence of a ring-like disk of circumstellar debris seen in 1.1
micron light scattered by the disk grains, surrounded by a di use outer region
of lower surface brightness. The annular disk appears to be inclined by 31.7
+/- 1.6 deg from face on with the disk major axis PA at 107 +/-2 deg . The
total 1.1 micron flux density of the light scattered by the disk (at 1.2" < r <
5.0") of 9.6 mJy +/- 0.8 mJy is 0.17% +/- 0.015% of the starlight. Seventy
percent of the light from the scattering grains appears to be confined in a 36
AU wide annulus centered on the peak of the radial surface brightness (SB)
profile 86.3 +/- 3.9 AU from the star, well beyond the characteristic radius of
thermal emission estimated from IRAS and Spitzer flux densities assuming
blackbody grains (~ 22 AU). The light scattered by the ring appears bilaterally
symmetric, exhibits directionally preferential scattering well represented by a
Henyey-Greenstein scattering phase function with g = 0.30 +/- 0.03, and has an
azimuthally medianed SB at the 86.3 AU radius of peak SB of 1.00 +/- 0.07 mJy
arcsec^-2. No photocentric offset is seen in the ring relative to the position
of the central star. A low surface brightness diffuse halo is seen in the
NICMOS image to a distance of ~ 4" Deeper 0.6 micron HST/ACS PSF-subtracted
coronagraphic observations reveal a faint outer nebulosity, asymmetrically
brighter to the North of the star. We discuss models of the disk and properties
of its grains, from which we infer a maximum vertical scale height of 4 - 8 AU
at the 87.6 AU radius of maximum surface density, and a total maximum dust mass
of collisionally replenished grains with minimum grain sizes of ~ 1 micron of ~
4 M(moon).Comment: 45 pages, 15 figures, accepted for publication in Ap
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