Josephson tunnel junction controlled by quasiparticle injection

A Josephson tunnel junction transistor based on quasiparticle injection is proposed. Its operation relies on the manipulation of the electron distribution in one of the junction electrodes. This is accomplished by injecting quasiparticle current through the junction electrode by two additional tunnel coupled superconductors. Both large supercurrent enhancement and fast quenching can be achieved with respect to equilibrium by varying quasiparticle injection for proper temperature regimes and suitable superconductor combinations. Joined with large power gain this makes the device attractive for applications where reduced noise and low power dissipation are required.Comment: 4 pages, 3 figure

Geometric Landau-Zener interferometry in a superconducting charge pump

We propose a new type of interferometry, based on geometric phases accumulated by a periodically driven two-level system undergoing multiple Landau-Zener transitions. As a specific example, we study its implementation in a superconducting charge pump. We find that interference patterns appear as a function of the pumping frequency and the phase bias, and clearly manifest themselves in the pumped charge. We also show that the effects described should persist in the presence of realistic decoherence.Comment: 5 pages, 3 figure

Statistics of heat exchange between two resistors

We study energy flow between two resistors coupled by an arbitrary linear and lossless electric circuit. We show that the fluctuations of energy transferred between the resistors are determined by random scattering of photons on an effective barrier with frequency dependent transmission probability $\tau(\omega)$. We express the latter in terms of the circuit parameters. Our results are valid in both quantum and classical regimes and for non-equilibrium electron distribution functions in the resistors.Comment: 7 pages, 4 figures. Published version. New figures added, discussion extende

A Josephson junction as a detector of Poissonian charge injection

We propose a scheme of measuring the non-Gaussian character of noise by a hysteretic Josephson junction in the macroscopic quantum tunnelling (MQT) regime. We model the detector as an (under)damped $LC$ resonator. It transforms Poissonian charge injection into current through the detector, which samples the injection statistics over a floating time window of length $\sim Q/\omega _{\rm J}$, where $Q$ is the quality factor of the resonator and $\omega_{\rm J}$ its resonance frequency. This scheme ought to reveal the Poisson character of charge injection in a detector with realistic parameters

Geometry of an adiabatic passage at a level crossing

We discuss adiabatic quantum phenomena at a level crossing. Given a path in the parameter space which passes through a degeneracy point, we find a criterion which determines whether the adiabaticity condition can be satisfied. For paths that can be traversed adiabatically we also derive a differential equation which specifies the time dependence of the system parameters, for which transitions between distinct energy levels can be neglected. We also generalize the well-known geometric connections to the case of adiabatic paths containing arbitrarily many level-crossing points and degenerate levels.Comment: 7 pages, 6 figures, RevTeX4, changes requested by Phys. Rev.