131 research outputs found
TLS Dynamics in a Superconducting Qubit Due to Background Ionizing Radiation
Superconducting qubit lifetimes must be both long and stable to provide an
adequate foundation for quantum computing. This stability is imperiled by
two-level systems (TLSs), currently a dominant loss mechanism, which exhibit
slow spectral dynamics that destabilize qubit lifetimes on hour timescales.
Stability is also threatened at millisecond timescales, where ionizing
radiation has recently been found to cause bursts of correlated multi-qubit
decays, complicating quantum error correction. Here we study both ionizing
radiation and TLS dynamics on a 27-qubit processor, repurposing the standard
transmon qubits as sensors of both radiation impacts and TLS dynamics. Unlike
prior literature, we observe resilience of the qubit lifetimes to the transient
quasiparticles generated by the impact of radiation. However, we also observe a
new interaction between these two processes, "TLS scrambling," in which a
radiation impact causes multiple TLSs to jump in frequency, which we suggest is
due to the same charge rearrangement sensed by qubits near a radiation impact.
As TLS scrambling brings TLSs out of or in to resonance with the qubit, the
lifetime of the qubit increases or decreases. Our findings thus identify
radiation as a new contribution to fluctuations in qubit lifetimes, with
implications for efforts to characterize and improve device stabilityComment: 14 pages, 10 figure
Faraday Tomography of the North Polar Spur: Constraints on the distance to the Spur and on the Magnetic Field of the Galaxy
We present radio continuum and polarization images of the North Polar Spur
(NPS) from the Global Magneto-Ionic Medium Survey (GMIMS) conducted with the
Dominion Radio Astrophysical Observatory 26-m Telescope. We fit polarization
angle versus wavelength squared over 2048 frequency channels from 1280 to 1750
MHz to obtain a Faraday Rotation Measure (RM) map of the NPS. Combining this RM
map with a published Faraday depth map of the entire Galaxy in this direction,
we derive the Faraday depth introduced by the NPS and the Galactic interstellar
medium (ISM) in front of and behind the NPS. The Faraday depth contributed by
the NPS is close to zero, indicating that the NPS is an emitting only feature.
The Faraday depth caused by the ISM in front of the NPS is consistent with zero
at b>50 degree, implying that this part of the NPS is local at a distance of
approximately several hundred parsecs. The Faraday depth contributed by the ISM
behind the NPS gradually increases with Galactic latitude up to b=44 degree,
and decreases at higher Galactic latitudes. This implies that either the part
of the NPS at b<44 degree is distant or the NPS is local but there is a sign
change of the large-scale magnetic field. If the NPS is local, there is then no
evidence for a large-scale anti-symmetry pattern in the Faraday depth of the
Milky Way. The Faraday depth introduced by the ISM behind the NPS at latitudes
b>50 degree can be explained by including a coherent vertical magnetic field.Comment: 9 pages, 8 figures, accepted for publication in ApJ. Some figures
have been degraded to reduce sizes, for a high resolution version, see
http://physics.usyd.edu.au/~xhsun/ms_nps.pd
Characterization of wetting using topological principles
Hypothesis Understanding wetting behavior is of great importance for natural
systems and technological applications. The traditional concept of contact
angle, a purely geometrical measure related to curvature, is often used for
characterizing the wetting state of a system. It can be determined from Young's
equation by applying equilibrium thermodynamics. However, whether contact angle
is a representative measure of wetting for systems with significant complexity
is unclear. Herein, we hypothesize that topological principles based on the
Gauss-Bonnet theorem could yield a robust measure to characterize wetting.
Theory and Experiments We introduce a macroscopic contact angle based on the
deficit curvature of the fluid interfaces that are imposed by contacts with
other immiscible phases. We perform sessile droplet simulations followed by
multiphase experiments for porous sintered glass and Bentheimer sandstone to
assess the sensitivity and robustness of the topological approach and compare
the results to other traditional approaches.
Findings We show that the presented topological principle is consistent with
thermodynamics under the simplest conditions through a variational analysis.
Furthermore, we elucidate that at sufficiently high image resolution the
proposed topological approach and local contact angle measurements are
comparable. While at lower resolutions, the proposed approach provides more
accurate results being robust to resolution-based effects. Overall, the
presented concepts open new pathways to characterize the wetting state of
complex systems and theoretical developments to study multiphase systems.Comment: 11 pages, 9 figures, 1 tabl
The GALFA-HI Compact Cloud Catalog
We present a catalog of 1964 isolated, compact neutral hydrogen clouds from
the Galactic Arecibo L-Band Feed Array Survey Data Release One (GALFA-HI DR1).
The clouds were identified by a custom machine-vision algorithm utilizing
Difference of Gaussian kernels to search for clouds smaller than 20'. The
clouds have velocities typically between |VLSR| = 20-400 km/s, linewidths of
2.5-35 km/s, and column densities ranging from 1 - 35 x 10^18 cm^-2. The
distances to the clouds in this catalog may cover several orders of magnitude,
so the masses may range from less than a Solar mass for clouds within the
Galactic disc, to greater than 10^4 Solar Masses for HVCs at the tip of the
Magellanic Stream. To search for trends, we separate the catalog into five
populations based on position, velocity, and linewidth: high velocity clouds
(HVCs); galaxy candidates; cold low velocity clouds (LVCs); warm, low
positive-velocity clouds in the third Galactic Quadrant; and the remaining warm
LVCs. The observed HVCs are found to be associated with previously-identified
HVC complexes. We do not observe a large population of isolated clouds at high
velocities as some models predict. We see evidence for distinct histories at
low velocities in detecting populations of clouds corotating with the Galactic
disc and a set of clouds that is not corotating.Comment: 34 Pages, 9 Figures, published in ApJ (2012, ApJ, 758, 44), this
version has the corrected fluxes and corresponding flux histogram and masse
Is the evidence for dark energy secure?
Several kinds of astronomical observations, interpreted in the framework of
the standard Friedmann-Robertson-Walker cosmology, have indicated that our
universe is dominated by a Cosmological Constant. The dimming of distant Type
Ia supernovae suggests that the expansion rate is accelerating, as if driven by
vacuum energy, and this has been indirectly substantiated through studies of
angular anisotropies in the cosmic microwave background (CMB) and of spatial
correlations in the large-scale structure (LSS) of galaxies. However there is
no compelling direct evidence yet for (the dynamical effects of) dark energy.
The precision CMB data can be equally well fitted without dark energy if the
spectrum of primordial density fluctuations is not quite scale-free and if the
Hubble constant is lower globally than its locally measured value. The LSS data
can also be satisfactorily fitted if there is a small component of hot dark
matter, as would be provided by neutrinos of mass 0.5 eV. Although such an
Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the
position of the `baryon acoustic oscillation' peak in the autocorrelation
function of galaxies, it may be possible to do so e.g. in an inhomogeneous
Lemaitre-Tolman-Bondi cosmology where we are located in a void which is
expanding faster than the average. Such alternatives may seem contrived but
this must be weighed against our lack of any fundamental understanding of the
inferred tiny energy scale of the dark energy. It may well be an artifact of an
oversimplified cosmological model, rather than having physical reality.Comment: 12 pages, 5 figures; to appear in a special issue of General
Relativity and Gravitation, eds. G.F.R. Ellis et al; Changes: references
reformatted in journal style - text unchange
GASKAP -- The Galactic ASKAP Survey
A survey of the Milky Way disk and the Magellanic System at the wavelengths
of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule
will be carried out with the Australian Square Kilometre Array Pathfinder
telescope. The survey will study the distribution of HI emission and absorption
with unprecedented angular and velocity resolution, as well as molecular line
thermal emission, absorption, and maser lines. The area to be covered includes
the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg,
spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire
area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The
brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K
at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific
goals, from studies of galaxy evolution to star formation, with particular
contributions to understanding stellar wind kinematics, the thermal phases of
the interstellar medium, the interaction between gas in the disk and halo, and
the dynamical and thermal states of gas at various positions along the
Magellanic Stream.Comment: 45 pages, 8 figures, Pub. Astron. Soc. Australia (in press
The Global Magneto-Ionic Medium Survey: A Faraday Depth Survey of the Northern Sky Covering 1280-1750 MHz
The Galactic interstellar medium hosts a significant magnetic field, which
can be probed through the synchrotron emission produced from its interaction
with relativistic electrons. Linearly polarized synchrotron emission is
generated throughout the Galaxy, and at longer wavelengths, modified along
nearly every path by Faraday rotation in the intervening magneto-ionic medium.
Full characterization of the polarized emission requires wideband observations
with many frequency channels. We have surveyed polarized radio emission from
the Northern sky over the the range 1280-1750 MHz, with channel width 236.8
kHz, using the John A. Galt Telescope (diameter 25.6 m) at the Dominion Radio
Astrophysical Observatory, as part of the Global Magneto-Ionic Medium Survey.
The survey covered 72% of the sky, declinations -30 to +87 degrees at all right
ascensions. The intensity scale was absolutely calibrated, based on the flux
density and spectral index of Cygnus A. Polarization angle was calibrated using
the extended polarized emission of the Fan Region. Data are presented as
brightness temperatures with angular resolution 40'. Sensitivity in Stokes Q
and U is 45 mK rms in a 1.18 MHz band. We have applied rotation measure
synthesis to the data to obtain a Faraday depth cube of resolution 150 radians
per square metre and sensitivity 3 mK rms of polarized intensity. Features in
Faraday depth up to a width of 110 radians per square metre are represented.
The maximum detectable Faraday depth is +/- 20,000 radians per square metre.
The survey data are available at the Canadian Astronomy Data Centre.Comment: Accepted for publication in the Astronomical Journa
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