89 research outputs found

    Kinetics of non-equilibrium quasiparticle tunneling in superconducting charge qubits

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    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

    Programmable networks for quantum algorithms

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    The implementation of a quantum computer requires the realization of a large number of N-qubit unitary operations which represent the possible oracles or which are part of the quantum algorithm. Until now there are no standard ways to uniformly generate whole classes of N-qubit gates. We have developed a method to generate arbitrary controlled phase shift operations with a single network of one-qubit and two-qubit operations. This kind of network can be adapted to various physical implementations of quantum computing and is suitable to realize the Deutsch-Jozsa algorithm as well as Grover's search algorithm.Comment: 4 pages. Accepted version; Journal-ref. adde

    Characterization of a Differential Radio-Frequency Single-Electron Transistor

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    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

    Non-ohmicity and energy relaxation in diffusive 2D metals

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    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

    The Quantum Capacitance Detector: A concept for a pair-breaking radiation detector based on the single Cooper-pair box

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    We present a proposed design for a pair-breaking photodetector for far-infrared and sub-millimeter radiation. Antenna-coupled radiation generates quasiparticles in a superconducting absorber, the density of which are measured using a single Cooper-pair box. Readout is performed using an electromagnetic oscillator or a microwave resonator, which is well suited for frequency multiplexing in large arrays. Theoretical limits to detector sensitivity are discussed and modeled, with predicted sensitivities rivaling transition-edge sensors and microwave kinetic inductance detectors. We anticipate that this detector can be used to address key scientific goals in far-infrared and sub-millimeter astronomy.Comment: 11 pages, 11 figures. Corrected expression for Fano noise NEP, improved Fig. 9, removed section on energy resolutio

    Universal saturation of electron dephasing in three-dimensional disordered metals

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    We have systematically investigated the low-temperature electron dephasing times τϕ\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 τ0\tau_0 [τϕ(T0K)\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 τ0\tau_0 scales with the electron diffusion constant DD as τ0Dα\tau_0 \sim D^{- \alpha}, with α\alpha close to or slightly larger than 1, for over two decades of DD from about 0.1 to 10 cm2^2/s. Our observation suggests that the saturation behavior of τϕ\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

    Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box

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    We analyse the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the environmentally-induced decoherence of the resonator superposition state.Comment: 4 pages, 3 figure