1,044 research outputs found
On the Josephson Coupling between a disk of one superconductor and a surrounding superconducting film of a different symmetry
A cylindrical Josephson junction with a spatially dependent Josephson
coupling which averages to zero is studied in order to model the physics of a
disk of d-wave superconductor embedded in a superconducting film of a different
symmetry. It is found that the system always introduces Josepshon vortices in
order to gain energy at the junction. The critical current is calculated. It is
argued that a recent experiment claimed to provide evidence for s-wave
superconductivity in may also be consistent with d-wave
superconductivity. Figures available from the author on request.Comment: 10 pages, revtex3.0, TM-11111-940321-1
Test Experiment for Time-Reversal Symmetry Breaking Superconductivity
A new experiment is proposed to probe the time-reversal symmetry of a
superconductor. It is shown that a time-reversal symmetry breaking
superconductor can be identified by the observation of a fractional flux in
connection with a Josephson junction in a special geometry.Comment: 4 pages, 2 figures available upon request, Revtex, MIT-CMT-OC
The use of multilayer network analysis in animal behaviour
Network analysis has driven key developments in research on animal behaviour
by providing quantitative methods to study the social structures of animal
groups and populations. A recent formalism, known as \emph{multilayer network
analysis}, has advanced the study of multifaceted networked systems in many
disciplines. It offers novel ways to study and quantify animal behaviour as
connected 'layers' of interactions. In this article, we review common questions
in animal behaviour that can be studied using a multilayer approach, and we
link these questions to specific analyses. We outline the types of behavioural
data and questions that may be suitable to study using multilayer network
analysis. We detail several multilayer methods, which can provide new insights
into questions about animal sociality at individual, group, population, and
evolutionary levels of organisation. We give examples for how to implement
multilayer methods to demonstrate how taking a multilayer approach can alter
inferences about social structure and the positions of individuals within such
a structure. Finally, we discuss caveats to undertaking multilayer network
analysis in the study of animal social networks, and we call attention to
methodological challenges for the application of these approaches. Our aim is
to instigate the study of new questions about animal sociality using the new
toolbox of multilayer network analysis.Comment: Thoroughly revised; title changed slightl
Observation and interpretation of motional sideband asymmetry in a quantum electro-mechanical device
Quantum electro-mechanical systems offer a unique opportunity to probe
quantum noise properties in macroscopic devices, properties which ultimately
stem from the Heisenberg Uncertainty Principle. A simple example of this is
expected to occur in a microwave parametric transducer, where mechanical motion
generates motional sidebands corresponding to the up and down
frequency-conversion of microwave photons. Due to quantum vacuum noise, the
rates of these processes are expected to be unequal. We measure this
fundamental imbalance in a microwave transducer coupled to a radio-frequency
mechanical mode, cooled near the ground state of motion. We also discuss the
subtle origin of this imbalance: depending on the measurement scheme, the
imbalance is most naturally attributed to the quantum fluctuations of either
the mechanical mode or of the electromagnetic field
Orthorhombically Mixed s and d Wave Superconductivity and Josephson Tunneling
The effect of orthorhombicity on Josephson tunneling in high T
superconductors such as YBCO is studied for both single crystals and highly
twinned crystals. It is shown that experiments on highly twinned crystals
experimentally determine the symmetry of the superconducting twin boundaries
(which can be either even or odd with respect to a reflection in the twinning
plane). Conversely, Josephson experiments on highly twinned crystals can not
experimentally determine whether the superconductivity is predominantly
-wave or predominantly -wave. The direct experimental determination of
the order-parameter symmetry by Josephson tunneling in YBCO thus comes from the
relatively few experiments which have been carried out on untwinned single
crystals.Comment: 5 pages, RevTeX file, 1 figure available on request
([email protected]
Quantum squeezing of motion in a mechanical resonator
As a result of the quantum, wave-like nature of the physical world, a
harmonic oscillator can never be completely at rest. Even in the quantum ground
state, its position will always have fluctuations, called the zero-point
motion. Although the zero-point fluctuations are unavoidable, they can be
manipulated. In this work, using microwave frequency radiation pressure, we
both prepare a micron-scale mechanical system in a state near the quantum
ground state and then manipulate its thermal fluctuations to produce a
stationary, quadrature-squeezed state. We deduce that the variance of one
motional quadrature is 0.80 times the zero-point level, or 1 dB of
sub-zero-point squeezing. This work is relevant to the quantum engineering of
states of matter at large length scales, the study of decoherence of large
quantum systems, and for the realization of ultra-sensitive sensing of force
and motion
X-ray spectral diagnostics of activity in massive stars
X-rays give direct evidence of instabilities, time-variable structure, and
shock heating in the winds of O stars. The observed broad X-ray emission lines
provide information about the kinematics of shock-heated wind plasma, enabling
us to test wind-shock models. And their shapes provide information about wind
absorption, and thus about the wind mass-loss rates. Mass-loss rates determined
from X-ray line profiles are not sensitive to density-squared clumping effects,
and indicate mass-loss rate reductions of factors of 3 to 6 over traditional
diagnostics that suffer from density-squared effects. Broad-band X-ray spectral
energy distributions also provide mass-loss rate information via soft X-ray
absorption signatures. In some cases, the degree of wind absorption is so high
that the hardening of the X-ray SED can be quite significant. We discuss these
results as applied to the early O stars zeta Pup (O4 If), 9 Sgr (O4 V((f))),
and HD 93129A (O2 If*).Comment: To appear in the proceedings of IAU 272: Active OB Star
Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
During the theoretical investigation of the ultimate sensitivity of
gravitational wave detectors through the 1970's and '80's, it was debated
whether quantum fluctuations of the light field used for detection, also known
as photon shot noise, would ultimately produce a force noise which would
disturb the detector and limit the sensitivity. Carlton Caves famously answered
this question with "They do." With this understanding came ideas how to avoid
this limitation by giving up complete knowledge of the detector's motion. In
these back-action evading (BAE) or quantum non-demolition (QND) schemes, one
manipulates the required quantum measurement back-action by placing it into a
component of the motion which is unobserved and dynamically isolated. Using a
superconducting, electro-mechanical device, we realize a sensitive measurement
of a single motional quadrature with imprecision below the zero-point
fluctuations of motion, detect both the classical and quantum measurement
back-action, and demonstrate BAE avoiding the quantum back-action from the
microwave photons by 9 dB. Further improvements of these techniques are
expected to provide a practical route to manipulate and prepare a squeezed
state of motion with mechanical fluctuations below the quantum zero-point
level, which is of interest both fundamentally and for the detection of very
weak forces
Polarization Selection Rules and Superconducting Gap Anisotropy in
We discuss polarization selection rules for angle-resolved photoemission
spectroscopy in Bi2212. Using these we show that the ``hump'' in the
superconducting gap observed in the quadrant in our earlier work is not on
the main band, but rather on an umklapp band arising from the
structural superlattice. The intrinsic gap is most likely quite small over a
range of about the diagonal directions.Comment: 3 pages, revtex, 3 uuencoded postscript figure
Demonstration of a Thermally Coupled Row-Column SNSPD Imaging Array
While single-pixel superconducting nanowire single photon detectors (SNSPDs) have demonstrated remarkable efficiency and timing performance from the UV to near-IR, scaling these devices to large imaging arrays remains challenging. Here, we propose a new SNSPD multiplexing system using thermal coupling and detection correlations between two photosensitive layers of an array. Using this architecture with the channels of one layer oriented in rows and the second layer in columns, we demonstrate imaging capability in 16-pixel arrays with accurate spot tracking at the few-photon level. We also explore the performance trade-offs of orienting the top layer nanowires parallel and perpendicular to the bottom layer. The thermally coupled row-column scheme is readily able to scale to the kilopixel size with existing readout systems and, when combined with other multiplexing architectures, has the potential to enable megapixel scale SNSPD imaging arrays
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