Kinetics of non-equilibrium quasiparticle tunneling in superconducting charge qubits

We directly observe low-temperature non-equilibrium quasiparticle tunneling in a pair of charge qubits based on the single Cooper-pair box. We measure even- and odd-state dwell time distributions as a function of temperature, and interpret these results using a kinetic theory. While the even-state lifetime is exponentially distributed, the odd-state distribution is more heavily weighted to short times, implying that odd-to-even tunnel events are not described by a homogenous Poisson process. The mean odd-state dwell time increases sharply at low temperature, which is consistent with quasiparticles tunneling out of the island before reaching thermal equilibrium.Comment: Replaced Figure 1 with color version, corrected more typos. Version submitted to PR

Characterization of a Differential Radio-Frequency Single-Electron Transistor

We have fabricated and characterized a new type of electrometer that couples two parallel single-electron transistors (SETs) to a radio-frequency tank circuit for use as a differential RF-SET. We demonstrate operation of this device in summing, differential, and single-SET operation modes, and use it to measure a Coulomb staircase from a differential single Cooper-pair box. In differential mode, the device is sensitive to uncorrelated input signals while screening out correlated ones.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter

Parametric Amplification and Back-Action Noise Squeezing by a Qubit-Coupled Nanoresonator

We demonstrate the parametric amplification and noise squeezing of nanomechanical motion utilizing dispersive coupling to a Cooper-pair box qubit. By modulating the qubit bias and resulting mechanical resonance shift, we achieve gain of 30 dB and noise squeezing of 4 dB. This qubit-mediated effect is 3000 times more effective than that resulting from the weak nonlinearity of capacitance to a nearby electrode. This technique may be used to prepare nanomechanical squeezed states

Large array of low-frequency readout quantum capacitance detectors

Quantum capacitance detectors (QCDs) are photon shot noise-limited terahertz detectors based on a single Cooper-pair box superconducting qubit. The QCD has demonstrated photon shot noise-limited performance for 1.5 THz radiation under loading conditions between 10⁻²⁰ and 10⁻¹⁸  W and single-photon detection and counting at that frequency. We report here fabrication and preliminary characterization of a 441 pixel array of QCDs with readout frequencies between 700 and 850 MHz

Non-ohmicity and energy relaxation in diffusive 2D metals

We analyze current-voltage characteristics taken on Au-doped indium-oxide films. By fitting a scaling function to the data, we extract the electron-phonon scattering rate as function of temperature, which yields a quadratic dependence of the electron-phonon scattering rate on temperature from 1K down to 0.28K. The origin of this enhanced electron-phonon scattering rate is ascribed to the mechanism proposed by Sergeev and Mitin.Comment: 7 pages, 6 figure

Upper Extremity Strength Characteristics in Female Recreational Tennis Players With and Without Lateral Epicondylalgia

STUDY DESIGN: Descriptive, cross-sectional. OBJECTIVES: To compare static strength characteristics of the upper extremity musculature in female recreational tennis players with lateral epicondylalgia to those of nonsymptomatic tennis players and a control group of women who did not play tennis. BACKGROUND: There is a paucity of research describing the relationship between lateral epicondylalgia and strength characteristics of the upper extremity musculature, despite the functional relationship between the shoulder, elbow, and wrist. METHODS: Sixty-three women were recruited into 3 groups (n = 21 per group): symptomatic tennis players (SIP) with lateral epicondylalgia, nonsymptomatic tennis players, and controls. Data collection was performed during a single session, during which the strength of selected muscle groups of the dominant upper extremity was measured using a combination of force transducers. Strength ratios of selected muscle groups were then calculated. RESULTS: The SIP group reported median pain level of 3/10 on a numeric pain rating scale and a symptom duration of 16 weeks. The SIP group had weaker lower trapezius strength (mean difference, -9.0 N; 95% confidence interval [CI]: -13.5, -4.4) and wrist extensor strength (-12.7 N; 95% CI: -24.4, -1.1), and a higher shoulder internal/external rotation strength ratio (0.19; 95% CI: 0.02, 0.35) and upper/lower trapezius strength ratio (1.32; 95% CI: 0.41, 2.23), compared to those of the nonsymptomatic group. Compared to the control group, the SIP group demonstrated a significantly higher shoulder internal/external rotation strength ratio (0.21; 95% CI: 0.04, 0.38) and wrist flexion/extension strength ratio (0.14; 95% CI: 0.01, 0.27). CONCLUSION: In this group of recreational female tennis players, significant differences in strength and strength ratio characteristics were identified. Although the design of the study precludes establishing a cause-and-effect relationship, the results suggest further study and treatment of the muscle groups of interest

Universal saturation of electron dephasing in three-dimensional disordered metals

We have systematically investigated the low-temperature electron dephasing times $\tau_\phi$ in more than 40 three-dimensional polycrystalline impure metals with distinct material characteristics. In all cases, a saturation of the dephasing time is observed below about a (few) degree(s) Kelvin, depending on samples. The value of the saturated dephasing time $\tau_0$ [$\equiv \tau_\phi (T \to 0 {\rm K})$] falls basically in the range 0.005 to 0.5 ns for all samples. Particularly, we find that $\tau_0$ scales with the electron diffusion constant $D$ as $\tau_0 \sim D^{- \alpha}$, with $\alpha$ close to or slightly larger than 1, for over two decades of $D$ from about 0.1 to 10 cm$^2$/s. Our observation suggests that the saturation behavior of $\tau_\phi$ is universal and intrinsic in three-dimensional polycrystalline impure metals. A complete theoretical explanation is not yet available.Comment: 4 pages, 3 eps figure