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

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

Intercalant-Driven Superconductivity in YbC6_{6} and CaC6_{6}

Recently deiscovered superconductivity in YbC$_6$ and CaC$_6$ 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$_6$ and CaCa$_6$, 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$_6$ and CaC$_6$, but not in alkaline-intercalated compounds, and explain the difference in $T_c$ by the ``isotope effect'' due to the difference in Yb and Ca atomic masses.Comment: 4 pages, embedded postscript figire

Two-gap superconductivity in MgB2_{2}: clean or dirty?

A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB$_{2}$. 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

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$\times10^{-17}$ W Hz$^{-1/2}$ 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

Simulated Extragalactic Observations with a Cryogenic Imaging Spectrophotometer

In this paper we explore the application of cryogenic imaging spectrophotometers. Prototypes of this new class of detector, such as superconducting tunnel junctions (STJs) and transition edge sensors (TESs), currently deliver low resolution imaging spectrophotometry with high quantum efficiency (70-100%) and no read noise over a wide bandpass in the visible to near-infrared. In order to demonstrate their utility and the differences in observing strategy needed to maximize their scientific return, we present simulated observations of a deep extragalactic field. Using a simple analytic technique, we can estimate both the galaxy redshift and spectral type more accurately than is possible with current broadband techniques. From our simulated observations and a subsequent discussion of the expected migration path for this new technology, we illustrate the power and promise of these devices.Comment: 30 pages, 10 figures, accepted for publication in the Astronomical Journa

"Chain scenario" for Josephson tunneling with pi-shift in YBa2Cu3O7

We point out that all current Josephson-junction experiments probing directly the symmetry of the superconducting state in YBa2Cu3O7, can be interpreted in terms of the bilayer antiferromagnetic spin fluctuation model, which renders the superconducting state with the order parameters of extended $s$ symmetry, but with the opposite signs in the bonding and antibonding Cu-O plane bands. The essential part of our interpretation includes the Cu-O chain band which would have the order parameter of the same sign as antibonding plane band. We show that in this case net Josephson currents along and perpendicular to the chains have the phase shift equal to pi.Comment: 4 pages, revtex, 1 figure uuencoded (POSTSCRIPT figure replaced - the previous file did not print Greek letters correctly

In-situ measurement of the permittivity of helium using microwave NbN resonators

By measuring the electrical transport properties of superconducting NbN quarter-wave resonators in direct contact with a helium bath, we have demonstrated a high-speed and spatially sensitive sensor for the permittivity of helium. In our implementation a $\sim10^{-3}$ mm$^3$ sensing volume is measured with a bandwidth of 300 kHz in the temperature range 1.8 to 8.8 K. The minimum detectable change of the permittivity of helium is calculated to be $\sim6\times$$10^{-11}$ $\epsilon_0$/Hz$^{1/2}$ with a sensitivity of order $10^{-13}$ $\epsilon_0$/Hz$^{1/2}$ easily achievable. Potential applications include operation as a fast, localized helium thermometer and as a transducer in superfluid hydrodynamic experiments.Comment: 4 pages, 3 figure

Optical Pulse-Phased Photopolarimetry of PSR B0656+14

We have observed the optical pulse profile of PSR B0656+14 in 10 phase bins at a high signal-to-noise ratio, and have measured the linear polarization profile over 30% of the pulsar period with some significance. The pulse profile is double-peaked, with a bridge of emission between the two peaks, similar to gamma-ray profiles observed in other pulsars. There is no detectable unpulsed flux, to a 1-sigma limit of 16% of the pulse-averaged flux. The emission in the bridge is highly (~ 100%) polarized, with a position angle sweep in excellent agreement with the prediction of the Rotating Vector Model as determined from radio polarization observations. We are able to account for the gross features of the optical light curve (i.e., the phase separation of the peaks) using both polar cap and outer gap models. Using the polar cap model, we are also able to estimate the height of the optical emission regions.Comment: 27 pages, 11 figures, accepted by ApJ (scheduled v597 n2, November 10, 2003