Browsing by Author "Hekking, F.W.J."
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- Effect of photon-assisted Andreev reflection in the accuracy of a SINIS turnstile
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2015-09-28) Di Marco, A.; Maisi, Ville; Hekking, F.W.J.; Pekola, JukkaWe consider a hybrid single-electron transistor constituted by a gate-controlled normal-metal island (N) connected to two voltage-biased superconducting leads (S) by means of two tunnel junctions (SINIS), operated as a turnstile. We show that the exchange of photons between this system and the high-temperature electromagnetic environment where it is embedded enhances Andreev reflection, thereby limiting the single-electron tunneling accuracy. - Leakage current of a superconductor-normal metal tunnel junction connected to a high-temperature environment
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013-11-11) Di Marco, A.; Maisi, Ville; Pekola, J.P.; Hekking, F.W.J.We consider a voltage-biased normal metal-insulator-superconductor (NIS) tunnel junction, connected to a high-temperature external electromagnetic environment. This model system features the commonly observed subgap leakage current in NIS junctions through photon-assisted tunneling which is detrimental for applications. We first consider a NIS junction directly coupled to the environment and analyze the subgap leakage current both analytically and numerically; we discuss the link with the phenomenological Dynes parameter. Then, we focus on a circuit where a low-temperature lossy transmission line is inserted between the NIS junction and the environment. We show that the amplitude of the transmitted frequencies relevant for the photon-assisted tunneling is exponentially suppressed as the length ℓ and the resistance per unit length R0 of the line are increased. Consequently, the subgap current is reduced exponentially as well. This property can not be obtained by means of lumped circuit elements. We finally discuss our results in view of the performance of NIS junctions in applications. - Measurement scheme of the Berry phase in superconducting circuits
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2006-06-26) Möttönen, M.; Pekola, J.P.; Vartiainen, Juha J.; Brosco, Valentina; Hekking, F.W.J.We present a measurement scheme for observing the Berry phase in a flux assisted Cooper pair pump—the Cooper pair sluice. In contrast to the recent experiments, in which the sluice was employed to generate accurate current through a resistance, we consider a device in a superconducting loop. This arrangement introduces a connection between the pumped current and the Berry phase accumulated during the adiabatic pumping cycles. From the adiabaticity criterion, we derive equations for the maximum pumped current and optimize the sluice accordingly. These results apply also to the high accuracy pumping which results in a potential candidate for a metrological current standard. For measuring the pumped current, an additional Josephson junction is installed into the superconducting loop. We show in detail that the switching of this system from superconducting state into normal state as a consequence of an external current pulse through it may be employed to probe the pumped current. To our knowledge the experimentalrealization of our scheme would be the first observation of the Berry phase in superconducting circuits. - Quantum Jump Approach for Work and Dissipation in a Two-Level System
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013-08-27) Hekking, F.W.J.; Pekola, J.P.We apply the quantum jump approach to address the statistics of work in a driven two-level system coupled to a heat bath. We demonstrate how this question can be analyzed by counting photons absorbed and emitted by the environment in repeated experiments. We find that the common nonequilibrium fluctuation relations are satisfied identically. The usual fluctuation-dissipation theorem for linear response applies for weak dissipation and/or weak drive. We point out qualitative differences between the classical and quantum regimes.