Browsing by Author "Pekola, J.P."

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  • Active Quasiparticle Suppression in a Non-Equilibrium Superconductor
    (2020-07-08) Marin Suarez, Marco; Peltonen, Joonas; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Quasiparticle (qp) poisoning is a major issue that impairs the operation of various superconducting devices. Even though these devices are often operated at temperatures well below the critical point where the number density of excitations is expected to be exponentially suppressed, their bare operation and stray microwave radiation excite the non-equilibrium qp’s. Here we use voltage-biased superconducting junctions to demonstrate and quantify qp extraction in the turnstile operation of a superconductor–insulator–normal metal–insulator–superconductor single-electron transistor. In this operation regime, excitations are injected into the superconducting leads at a rate proportional to the driving frequency. We reach a reduction of density by an order of magnitude even for the highest injection rate of 2.4 × 108 qp’s per second when extraction is turned on.
  • 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.
  • Calorimetric measurement of work in a quantum system
    (2013-11-12) Pekola, J.P.; Solinas, P.; Shnirman, A.; Averin, D.V.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We propose a calorimetric measurement of work in a quantum system. As a physical realization, we consider a superconducting two-level system, a Cooper-pair box, driven by a gate voltage past an avoided level crossing at charge degeneracy. We demonstrate that, with realistic experimental parameters, the temperature measurement of a resistor (environment) can detect single microwave photons emitted or absorbed by the two-level system. This method would thus be a way to measure the full distribution of work in repeated measurements, and to assess the quantum fluctuation relations.
  • Environment-assisted tunneling as an origin of the Dynes density of states
    (2010-07-06) Pekola, J.P.; Maisi, Ville; Kafanov, Sergey; Chekurov, Nikolai; Kemppinen, A.; Pashkin, Yu.A.; Saira, O.-P.; Möttönen, M.; Tsai, J.S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We show that the effect of a high-temperature environment in current transport through a normal metal–insulator–superconductor tunnel junction can be described by an effective density of states in the superconductor. In the limit of a resistive low-Ohmic environment, this density of states reduces into the well-known Dynes form. Our theoretical result is supported by experiments in engineered environments. We apply our findings to improve the performance of a single-electron turnstile, a potential candidate for a metrological current source.
  • Environment-Governed Dynamics in Driven Quantum Systems
    (2013-04-12) Gasparinetti, S.; Solinas, P.; Pugnetti, S.; Fazio, Rosario; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We show that the dynamics of a driven quantum system weakly coupled to the environment can exhibit two distinct regimes. While the relaxation basis is usually determined by the system+drive Hamiltonian (system-governed dynamics), we find that under certain conditions it is determined by specific features of the environment, such as, the form of the coupling operator (environment-governed dynamics). We provide an effective coupling parameter describing the transition between the two regimes and discuss how to observe the transition in a superconducting charge pump.
  • Evanescent states and nonequilibrium in driven superconducting nanowires
    (2012-06-04) Vercruyssen, N.; Verhagen, T.G.A.; Flokstra, M.G.; Pekola, J.P.; Klapwijk, T.M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the nonlinear response of current transport in a superconducting diffusive nanowire between normal reservoirs. We demonstrate theoretically and experimentally the existence of two different superconducting states appearing when the wire is driven out of equilibrium by an applied bias, called the global and bimodal superconducting states. The different states are identified by using two-probe measurements of the wire, and measurements of the local density of states with tunneling probes. The analysis is performed within the framework of the quasiclassical kinetic equations for diffusive superconductors.
  • Excitation of single quasiparticles in a small superconducting Al island connected to normal-metal leads by tunnel junctions
    (2013-10-03) Maisi, Ville; Lotkhov, S.V.; Kemppinen, A.; Heimes, A.; Muhonen, J.T.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We investigate the dynamics of individual quasiparticle excitations on a small superconducting aluminum island connected to normal metallic leads by tunnel junctions. We find the island to be free of excitations within the measurement resolution. This allows us to show that the residual heating, which typically limits experiments on superconductors, has an ultralow value of less than 0.1 aW. By injecting electrons with a periodic gate voltage, we probe electron-phonon interaction and relaxation down to a single quasiparticle excitation pair, with a measured recombination rate of 16 kHz. Our experiment yields a strong test of BCS theory in aluminum as the results are consistent with it without free parameters.
  • Experimental Observation of the Role of Mutual Information in the Nonequilibrium Dynamics of a Maxwell Demon
    (2014-07-14) Koski, J.V.; Maisi, Ville; Sagawa, T.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We validate experimentally a fluctuation relation known as generalized Jarzynski equality governing the work distribution in a feedback-controlled system. The feedback control is performed on a single electron box analogously to the original Szilard engine. In the generalized Jarzynski equality, mutual information is treated on an equal footing with the thermodynamic work. Our measurements provide the first evidence of the role of mutual information in the fluctuation theorem and thermodynamics of irreversible processes.
  • Experimental realization of a Coulomb blockade refrigerator
    (2014-11-24) Feshchenko, A.V.; Koski, J.V.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present an experimental realization of a Coulomb blockade refrigerator (CBR) based on a single-electron transistor (SET). In the present structure, the SET island is interrupted by a superconducting inclusion to permit charge transport while preventing heat flow. At certain values of the bias and gate voltages, the current through the SET cools one of the junctions. The measurements follow the theoretical model down to ∼80 mK, which was the base temperature of the current measurements. The observed cooling increases rapidly with decreasing temperature, in agreement with the theory, reaching about a 15 mK drop at the base temperature. The CBR appears as a promising electronic cooler at temperatures well below 100 mK.
  • Fast Electron Thermometry for Ultrasensitive Calorimetric Detection
    (2015) Gasparinetti, S.; Viisanen, Klaara; Saira, Olli-Pentti; Faivre, T.; Arzeo, M.; Meschke, M.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We demonstrate radio-frequency thermometry on a micrometer-sized metallic island below 100 mK. Our device is based on a normal-metal–insulator–superconductor tunnel junction coupled to a resonator with transmission readout. In the first generation of the device, we achieve 90  μK/√Hz noise-equivalent temperature with 10 MHz bandwidth. We measure the thermal relaxation time of the electron gas in the island, which we find to be of the order of 100  μs. Such a calorimetric detector, upon optimization, can be seamlessly integrated into superconducting circuits, with immediate applications in quantum-thermodynamics experiments down to single quanta of energy.
  • Fluctuation relations for driven coupled classical two-level systems with incomplete measurements
    (2015-01-28) Borrelli, M.; Koski, Jonne; Maniscalco, S.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We theoretically investigate fluctuation relations in a classical incomplete measurement process where only partial information is available. The scenario we consider consists of two coupled single-electron boxes where one or both devices can undergo a nonequilibrium transformation according to a chosen protocol. The entropy production of only one of the two boxes is recorded and fluctuation relations for this quantity are put to a test, showing strong modifications whose nature depends upon the specific case study.
  • Geometric Landau-Zener Interferometry
    (2011-11-11) Gasparinetti, S.; Solinas, P.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.
  • Heat due to system-reservoir correlations in thermal equilibrium
    (2014-08-22) Ankerhold, Joachim; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The heat flow between a quantum system and its reservoir is analyzed when initially both are in a separable thermal state and asymptotically approach a correlated equilibrium. General findings are illustrated for specific systems and various classes of non-Markovian reservoirs relevant for solid state realizations. System-bath correlations are shown to be substantial at low temperatures even in the weak coupling regime. As a consequence, predictions of work and heat for actual experiments obtained within conventional perturbative approaches may often be questionable. Correlations induce characteristic imprints in heat capacities which opens a proposal to measure them in solid state devices.
  • InstituteQ - The Finnish National Quantum Institute
    (2022-04-20) Gunes, Minna; Majumdar, Himadri S.; Muratore Ginanneschi, Paolo; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Leakage current of a superconductor-normal metal tunnel junction connected to a high-temperature environment
    (2013-11-11) Di Marco, A.; Maisi, Ville; Pekola, J.P.; Hekking, F.W.J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.
  • Magnetic-field-induced stabilization of nonequillibrium superconductivity in a normal-metal/insulator/superconductor junction
    (2011-12-14) Peltonen, J.T.; Muhonen, J.T.; Meschke, M.; Kopnin, N.B.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A small magnetic field is found to enhance relaxation processes in a superconductor, thus stabilizing superconductivity in nonequilibrium conditions. In a normal-metal (N)/insulator/superconductor (S) tunnel junction, applying a field of the order of 100μT leads to significantly improved cooling of the N island by quasiparticle (QP) tunneling. These findings are attributed to faster QP relaxation within the S electrodes as a result of enhanced QP drain through regions with a locally suppressed energy gap due to magnetic vortices in the S leads at some distance from the junction.
  • Maxwell's demon based on a single-electron pump
    (2011-12-27) Averin, D.; Möttönen, M.; Pekola, J.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We propose and analyze a possible implementation of Maxwell's demon (MD) based on a single-electron pump. It presents a practical realization of MD in a solid-state environment. We show that measurements of the charge states of the pump and feedback control of the gate voltages lead to a net flow of electrons against the bias voltage ideally with no work done on the system by the gate control. The information obtained in the measurements converts thermal fluctuations into energy stored in a capacitor. We derive the conditions on the detector back action and measurement time necessary for implementing this conversion.
  • Measurement scheme for the Lamb shift in a superconducting circuit with broadband environment
    (2011-11-09) Gramich, V.; Solinas, P.; Möttönen, M.; Pekola, J.P.; Ankerhold, Joachim
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Motivated by recent experiments on quantum mechanical charge pumping in a Cooper pair sluice, we present a measurement scheme for observing shifts of transition frequencies in two-level quantum systems induced by broadband environmental fluctuations. In contrast to quantum optical and related setups based on cavities, the impact of a thermal phase reservoir is considered. A thorough analysis of Lamb and Stark shifts within weak-coupling master equations is complemented by nonperturbative results for the model of an exactly solvable harmonic system. The experimental protocol to measure the Lamb shift in experimentally feasible superconducting circuits is analyzed in detail and supported by numerical simulations.
  • Measurement scheme of the Berry phase in superconducting circuits
    (2006-06-26) Möttönen, M.; Pekola, J.P.; Vartiainen, Juha J.; Brosco, Valentina; Hekking, F.W.J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.
  • Moments of work in the two-point measurement protocol for a driven open quantum system
    (2014-09-22) Suomela, S.; Solinas, P.; Pekola, J.P.; Ankerhold, Joachim; Ala-Nissila, T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the distribution of work induced by the two-point measurement protocol for a driven open quantum system. We first derive a general form for the generating function of work for the total system, bearing in mind that the Hamiltonian does not necessarily commute with its time derivative. Using this result, we then study the first few moments of work by using the master equation of the reduced system, invoking approximations similar to the ones made in the microscopic derivation of the reduced density matrix. Our results show that already in the third moment of work, correction terms appear that involve commutators between the Hamiltonian and its time derivative. To demonstrate the importance of these terms, we consider a sinusoidally, weakly driven and weakly coupled open two-level quantum system, and indeed find that already in the third moment of work, the correction terms are significant. We also compare our results to those obtained with the quantum jump method and find a good agreement.