1,502 research outputs found
Multiplexable Kinetic Inductance Detectors
We are starting to investigate a novel multiplexable readout method that can be applied to a large class of superconducting pair-breaking detectors. This readout method is completely different from those currently used with STJ and TES detectors, and in principle could deliver large pixel counts, high sensitivity, and Fano-limited spectral resolution. The readout is based on the fact that the kinetic surface inductance L_s of a superconductor is a function of the density of quasiparticles n, even at temperatures far below T_c. An efficient way to measure changes in the kinetic inductance is to monitor the transmission phase of a resonant circuit. By working at microwave frequencies and using thin films, the kinetic inductance can be a significant part of the total inductance L, and the volume of the inductor can be made quite small, on the order of 1 µm^3. As is done with other superconducting detectors, trapping could be used to concentrate the quasiparticles into the small volume of the inductor. However, the most intriguing aspect of the concept is that passive frequency multiplexing could be used to read out ~10^3 detectors with a single HEMT amplifier
Phase-sensitive tests of the pairing state symmetry in Sr2RuO4
Exotic superconducting properties of SrRuO have provided strong
support for an unconventional pairing symmetry. However, the extensive efforts
over the past decade have not yet unambiguously resolved the controversy about
the pairing symmetry in this material. While recent phase-sensitive experiments
using flux modulation in Josephson junctions consisting of SrRuO
and a conventional superconductor have been interpreted as conclusive evidence
for a chiral spin-triplet pairing, we propose here an alternative
interpretation. We show that an overlooked chiral spin-singlet pairing is also
compatible with the observed phase shifts in Josephson junctions and propose
further experiments which would distinguish it from its spin-triplet
counterpart.Comment: 4 pages, 1 figur
Mesoscopic Cavity Quantum Electrodynamics with Quantum Dots
We describe an electrodynamic mechanism for coherent, quantum mechanical
coupling between spacially separated quantum dots on a microchip. The technique
is based on capacitive interactions between the electron charge and a
superconducting transmission line resonator, and is closely related to atomic
cavity quantum electrodynamics. We investigate several potential applications
of this technique which have varying degrees of complexity. In particular, we
demonstrate that this mechanism allows design and investigation of an on-chip
double-dot microscopic maser. Moreover, the interaction may be extended to
couple spatially separated electron spin states while only virtually populating
fast-decaying superpositions of charge states. This represents an effective,
controllable long-range interaction, which may facilitate implementation of
quantum information processing with electron spin qubits and potentially allow
coupling to other quantum systems such as atomic or superconducting qubits.Comment: 8 pages, 5 figure
Torsional Behavior of RC beams Strengthened by Near Surface Mounted-Steel Wire Rope Under Repeated Loading
In this paper, the torsional behavior of strengthened beams, which were subjected to constant and incremental repeated loads is studied. Repeated loads have a negative effect on the strength of beams as they reduce the beams resistance to external loads. External strengthening is usually used to increase the strength of beams for different applied loading. The near-surface mounted technique is a type of strengthening recently used to improve the strength of beams. The experimental program includes testing of twelve beams. All beams have the same dimensions and the same reinforcement. Nine of those beams are strengthened with different configurations of steel wire rope, and three beams are non-strengthened (reference beams). The results show that the decreasing of the spacing between wires (increasing the amount of steel wires) leads to an increase in the beam torsion strength and a decrease in the twist angle of beams. All strengthened beams show high resistance to the repeated load, especially constant repeated load, the increased torsional capacity has reached to 181.12% in beams under constant repeated load compared to the related beam subjected to monotonic load
Study of loss in superconducting coplanar waveguide resonators
Superconducting coplanar waveguide (SCPW) resonators have a wide range of
applications due to the combination of their planar geometry and high quality
factors relative to normal metals. However, their performance is sensitive to
both the details of their geometry and the materials and processes that are
used in their fabrication. In this paper, we study the dependence of SCPW
resonator performance on materials and geometry as a function of temperature
and excitation power. We measure quality factors greater than at
high excitation power and at a power comparable to that generated
by a single microwave photon circulating in the resonator. We examine the
limits to the high excitation power performance of the resonators and find it
to be consistent with a model of radiation loss. We further observe that while
in all cases the quality factors are degraded as the temperature and power are
reduced due to dielectric loss, the size of this effect is dependent on
resonator materials and geometry. Finally, we demonstrate that the dielectric
loss can be controlled in principle using a separate excitation near the
resonance frequencies of the resonator.Comment: Replacing original version. Changes made based on referee comments.
Fixed typo in equation (3) and added appendi
Intercalant-Driven Superconductivity in YbC and CaC
Recently deiscovered superconductivity in YbC and CaC at temperatures
substantially higher than previously known for intercalated graphites, raised
several new questions: (1) Is the mechanism considerably different from the
previously known intercalated graphites? (2) If superconductivity is
conventional, what are the relevant phonons? (3) Given extreme similarity
between YbC and CaCa, why their critical temperatures are so different?
We address these questions on the basis of first-principles calculations and
conclude that coupling with intercalant phonons is likely to be the main force
for superconductivity in YbC and CaC, but not in alkaline-intercalated
compounds, and explain the difference in by the ``isotope effect'' due to
the difference in Yb and Ca atomic masses.Comment: 4 pages, embedded postscript figire
Two-gap superconductivity in MgB: clean or dirty?
A large number of experimental facts and theoretical arguments favor a
two-gap model for superconductivity in MgB. However, this model predicts
strong suppression of the critical temperature by interband impurity scattering
and, presumably, a strong correlation between the critical temperature and the
residual resistivity. No such correlation has been observed. We argue that this
fact can be understood if the band disparity of the electronic structure is
taken into account, not only in the superconducting state, but also in normal
transport
Optical Properties and Correlation Effects in NaxCoO2
We have calculated the optical spectra of NaCoO for =0.3, 0.5,
and 0.7 within the LDA. We compare our results to available experimental data
and show that the important features and trends are reproduced well, but there
is a nearly uniform shift of peak positions and poor agreement in intensities.
We show, through application of a simple model, that these differences can be
attributed to overhybridization between Co and O orbitals and spin fluctuations
which renormalize the bandwidth. Applying the LDA+U procedure shifts the
optical peaks further from their experimental locations, indicating that this
method of incorporating correlation effects is ill-suited for the case NaxCoO2
Pinpointing Gap Minima in Ba(FeCoAs \textit{via} Band Structure Calculations and Electronic Raman Scattering
A detailed knowledge of the gap structure for the Fe-pnictide superconductors
is still rather rudimentary, with several conflicting reports of either nodes,
deep gap minima, or fully isotropic gaps on the Fermi surface sheets, both in
the plane and along the c-axis. In this paper we present
considerations for electronic Raman scattering which can help clarify the gap
structure and topology using different light scattering geometries. Using
density functional calculations for the Raman vertices, it is shown that the
location of the gap minima may occur on loops stretching over a portion of the
c-axis in Ba(FeCoAs.Comment: 4+ pages, three figure
Thin film dielectric microstrip kinetic inductance detectors
Microwave Kinetic Inductance Detectors, or MKIDs, are a type of low
temperature detector that exhibit intrinsic frequency domain multiplexing at
microwave frequencies. We present the first theory and measurements on a MKID
based on a microstrip transmission line resonator. A complete characterization
of the dielectric loss and noise properties of these resonators is performed,
and agrees well with the derived theory. A competitive noise equivalent power
of 5 W Hz at 1 Hz has been demonstrated. The
resonators exhibit the highest quality factors known in a microstrip resonator
with a deposited thin film dielectric.Comment: 10 pages, 4 figures, APL accepte
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