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A practical quantum computer, if built, would consist of a set of coupled two-level quantum systems (qubits). Among the variety of qubits implemented, solid-state qubits are of particular interest because of their potential suitability for integrated devices. A variety of qubits based on Josephson junctions have been implemented; these exploit the coherence(More)
We have calculated all the components of the current in a short one-dimensional channel between two superconductors for arbitrary voltages and transparencies D of the channel. We demonstrate that in the ballistic limit (D ≃ 1), the crossover between the quasistationary evolution of the Joseph-son phase difference ϕ at small voltages and transport by(More)
The existing theory of correlated single-electron tunneling in the double normal-metal tunnel junction is extended to the case of an ultrasmall central electrode of the structure. It is shown that the form of the I-V curve of such a system depends on the energy relaxation rate in this electrode. For realistic values of the relaxation rate, the large-scale(More)
We suggest and demonstrate in experiment that two normal metal /insulator/ superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistances 1.0 and 1.1 kΩ is capable of reaching a temperature(More)
We report the observation of the universal distribution of transparencies, predicted by Schep and Bauer [Phys. Rev. Lett. 78, 3015 (1997)] for dirty sharp interfaces, in uniform Nb/AlO(x)/Nb junctions with high specific conductance (10(8) ohm(-1) cm(-2)). Experiments used the BCS density of states in superconducting niobium for transparency distribution(More)
We develop a theory of quadratic quantum measurements by a mesoscopic detector. It is shown that the quadratic measurements should have nontrivial quantum information properties, providing, for instance, a simple way of entangling two noninteracting qubits. We also calculate the output spectrum of a detector with both linear and quadratic response,(More)