593 research outputs found
Identifying capacitive and inductive loss in lumped element superconducting hybrid titanium nitride/aluminum resonators
We present a method to systematically locate and extract capacitive and
inductive losses in superconducting resonators at microwave frequencies by use
of mixed-material, lumped element devices. In these devices, ultra-low loss
titanium nitride was progressively replaced with aluminum in the
inter-digitated capacitor and meandered inductor elements. By measuring the
power dependent loss at 50 mK as the Al-TiN fraction in each element is
increased, we find that at low electric field, i.e. in the single photon limit,
the loss is two level system in nature and is correlated with the amount of Al
capacitance rather than the Al inductance. In the high electric field limit,
the remaining loss is linearly related to the product of the Al area times its
inductance and is likely due to quasiparticles generated by stray radiation. At
elevated temperature, additional loss is correlated with the amount of Al in
the inductance, with a power independent TiN-Al interface loss term that
exponentially decreases as the temperature is reduced. The TiN-Al interface
loss is vanishingly small at the 50 mK base temperature.Comment: 10 pages, 5 figure
Coherence in a transmon qubit with epitaxial tunnel junctions
We developed transmon qubits based on epitaxial tunnel junctions and
interdigitated capacitors. This multileveled qubit, patterned by use of
all-optical lithography, is a step towards scalable qubits with a high
integration density. The relaxation time T1 is .72-.86mu sec and the ensemble
dephasing time T2 is slightly larger than T1. The dephasing time T2 (1.36mu
sec) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker
level splitting than observed in qubits with amorphous barriers in
equivalent-size junctions. The qubit's inferred microwave loss closely matches
the weighted losses of the individual elements (junction, wiring dielectric,
and interdigitated capacitor), determined by independent resonator
measurements
Dielectric loss of boron-based dielectrics on niobium resonators
Advanced solid-state quantum bits (qubits) are likely to require a variety of dielectrics for wiring crossovers, substrates, and Josephson junctions. Microwave superconducting resonators are an excellent tool for measuring the internal dielectric loss of materials. We report the dielectric loss of boron-based dielectric films using a microwave coplanar waveguide (CPW) resonator with heterostructure geometry. Power-dependent internal quality factors of magnetron-sputtered boron carbide ( B4C ) and boron nitride (BN) were measured and are compared to silicon oxide ( SiO2 ), a common material used in wiring crossovers. The internal dielectric loss due to two-level systems for B4C , and BN is less than silicon dioxide ( SiO2 ), which demonstrates the existence of low-loss sputtered materials. We also found that niobium (Nb) CPW resonators suffer a decrease in internal quality factor after deposition of B4C at temperatures above 150 ∘C . This result is consistent with the idea that the oxidation of the surface of the superconducting metal can contribute to loss in a device
Quark Gluon Plasma an Color Glass Condensate at RHIC? The perspective from the BRAHMS experiment
We review the main results obtained by the BRAHMS collaboration on the
properties of hot and dense hadronic and partonic matter produced in
ultrarelativistic heavy ion collisions at RHIC. A particular focus of this
paper is to discuss to what extent the results collected so far by BRAHMS, and
by the other three experiments at RHIC, can be taken as evidence for the
formation of a state of deconfined partonic matter, the so called
quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor
state to the QGP, i.e. the proposed Color Glass Condensate.Comment: 32 pages, 18 figure
Brain size and brain/intracranial volume ratio in major mental illness
<p>Abstract</p> <p>Background</p> <p>This paper summarizes the findings of a long term study addressing the question of how several brain volume measure are related to three major mental illnesses in a Colorado subject group. It reports results obtained from a large N, collected and analyzed by the same laboratory over a multiyear period, with visually guided MRI segmentation being the primary initial analytic tool.</p> <p>Methods</p> <p>Intracerebral volume (ICV), total brain volume (TBV), ventricular volume (VV), ventricular/brain ratio (VBR), and TBV/ICV ratios were calculated from a total of 224 subject MRIs collected over a period of 13 years. Subject groups included controls (C, N = 89), and patients with schizophrenia (SZ, N = 58), bipolar disorder (BD, N = 51), and schizoaffective disorder (SAD, N = 26).</p> <p>Results</p> <p>ICV, TBV, and VV measures compared favorably with values obtained by other research groups, but in this study did not differ significantly between groups. TBV/ICV ratios were significantly decreased, and VBR increased, in the SZ and BD groups compared to the C group. The SAD group did not differ from C on any measure.</p> <p>Conclusions</p> <p>In this study TBV/ICV and VBR ratios separated SZ and BD patients from controls. Of interest however, SAD patients did not differ from controls on these measures. The findings suggest that the gross measure of TBV may not reliably differ in the major mental illnesses to a degree useful in diagnosis, likely due to the intrinsic variability of the measures in question; the differences in VBR appear more robust across studies. Differences in some of these findings compared to earlier reports from several laboratories finding significant differences between groups in VV and TBV may relate to phenomenological drift, differences in analytic techniques, and possibly the "file drawer problem".</p
Measurement of Muon Neutrino Quasi-Elastic Scattering on Carbon
The observation of neutrino oscillations is clear evidence for physics beyond
the standard model. To make precise measurements of this phenomenon, neutrino
oscillation experiments, including MiniBooNE, require an accurate description
of neutrino charged current quasi-elastic (CCQE) cross sections to predict
signal samples. Using a high-statistics sample of muon neutrino CCQE events,
MiniBooNE finds that a simple Fermi gas model, with appropriate adjustments,
accurately characterizes the CCQE events observed in a carbon-based detector.
The extracted parameters include an effective axial mass, M_A^eff = 1.23+/-0.20
GeV, that describes the four-momentum dependence of the axial-vector form
factor of the nucleon; and a Pauli-suppression parameter, kappa =
1.019+/-0.011. Such a modified Fermi gas model may also be used by future
accelerator-based experiments measuring neutrino oscillations on nuclear
targets.Comment: 5 pages, 3 figure
Search for gravitational wave bursts in LIGO's third science run
We report on a search for gravitational wave bursts in data from the three
LIGO interferometric detectors during their third science run. The search
targets subsecond bursts in the frequency range 100-1100 Hz for which no
waveform model is assumed, and has a sensitivity in terms of the
root-sum-square (rss) strain amplitude of hrss ~ 10^{-20} / sqrt(Hz). No
gravitational wave signals were detected in the 8 days of analyzed data.Comment: 12 pages, 6 figures. Amaldi-6 conference proceedings to be published
in Classical and Quantum Gravit
First LIGO search for gravitational wave bursts from cosmic (super)strings
We report on a matched-filter search for gravitational wave bursts from
cosmic string cusps using LIGO data from the fourth science run (S4) which took
place in February and March 2005. No gravitational waves were detected in 14.9
days of data from times when all three LIGO detectors were operating. We
interpret the result in terms of a frequentist upper limit on the rate of
gravitational wave bursts and use the limits on the rate to constrain the
parameter space (string tension, reconnection probability, and loop sizes) of
cosmic string models.Comment: 11 pages, 3 figures. Replaced with version submitted to PR
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
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