Browsing by Author "Hekking, F.W."

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  • Brownian refrigeration by hybrid tunnel junctions
    (2011-10-04) Peltonen, J.T.; Helle, Meri; Timofeev, A.V.; Solinas, P.; Hekking, F.W.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Voltage fluctuations generated in a hot resistor can cause extraction of heat from a colder normal metal electrode of a hybrid tunnel junction between a normal metal and a superconductor. We extend the analysis presented in Phys. Rev. Lett. 98, 210604 (2007) of this heat rectifying system, bearing resemblance to a Maxwell’s demon. Explicit analytic calculations show that the entropy of the total system is always increasing. We then consider a single-electron transistor configuration with two hybrid junctions in series, and show how the cooling is influenced by charging effects. We analyze also the cooling effect from nonequilibrium fluctuations instead of thermal noise, focusing on the shot noise generated in another tunnel junction. We conclude by discussing limitations for an experimental observation of the effect.
  • Measurement of coherent charge transfer in an adiabatic Cooper-pair pump
    (2003-08-07) Fazio, Rosario; Hekking, F.W.; Pekola, Jukka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study adiabatic charge transfer in a superconducting Cooper-pair pump, focusing on the influence of current measurement on coherence. We investigate the limit where the Josephson coupling energy EJ between the various parts of the system is small compared to the Coulomb charging energy EC. In this case, the charge transferred in a pumping cycle QP∼2e, the charge of one Cooper pair: The main contribution is due to incoherent Cooper-pair tunneling. We are particularly interested in the quantum correction to QP, which is due to coherent tunneling of pairs across the pump and which depends on the superconducting phase difference φ0 between the electrodes; 1−QP/(2e)∼(EJ/EC)cosφ0. A measurement of QP tends to destroy the phase coherence. We first study an arbitrary measuring circuit and then specific examples and show that coherent Cooper-pair transfer can, in principle, be detected using an inductively shunted ammeter.