Browsing by Author "Pekola, J. P."
Now showing 1 - 20 of 43
- Results Per Page
- Sort Options
- Anomalous electronic heat capacity of copper nanowires at sub-Kelvin temperatures
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-03-15) Viisanen, K. L.; Pekola, J. P.We have measured the electronic heat capacity of thin film nanowires of copper and silver at temperatures 0.1-0.3 K; the films were deposited by standard electron-beam evaporation. The specific heat of the Ag films of sub-100-nm thickness agrees with the bulk value and the free-electron estimate, whereas that of similar Cu films exceeds the corresponding reference values by one order of magnitude. The origin of the anomalously high heat capacity of copper films remains unknown for the moment. Based on the small heat capacity at low temperatures and the possibility to devise a tunnel probe thermometer on it, metal films form a promising absorber material, e.g., for microwave photon calorimetry. - Applications of Superconductor–Normal Metal Interfaces
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-10) Lemziakov, S. A.; Karimi, B.; Nakamura, S.; Lvov, D. S.; Upadhyay, R.; Satrya, C. D.; Chen, Z. Y.; Subero, D.; Chang, Y. C.; Wang, L. B.; Pekola, J. P.The importance and non-trivial properties of superconductor normal metal interfaces were discovered by Alexander Fyodorovich Andreev more than 60 years ago. Only much later, these hybrids have found wide interest in applications such as thermometry and refrigeration, electrical metrology, and quantum circuit engineering. Here we discuss the central properties of such interfaces and describe some of the most prominent and recent applications of them. - Cascade Electronic Refrigerator Using Superconducting Tunnel Junctions
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-11-23) Nguyen, Hung; Peltonen, Joonas; Meschke, M.; Pekola, J. P.Microrefrigerators that operate in the subkelvin regime are key devices in quantum technology. A well-studied candidate, an electronic cooler using normal-metal-insulator-superconductor (N-I-S) tunnel junctions, offers substantial performance and power. However, its superconducting electrodes are severely overheated due to exponential suppression of their thermal conductance towards low temperatures, and the cooler performs unsatisfactorily - especially in powerful devices needed for practical applications. We employ a second N-I-S cooling stage to thermalize the hot superconductor at the backside of the main N-I-S cooler. Not only providing a lower bath temperature, the second-stage cooler actively evacuates quasiparticles out of the hot superconductor, especially in the low-temperature limit. We demonstrate the apparent advantage of our approach. This cascade design can also be employed to manage excess heat in other cryoelectronic devices. - Charge-vortex interplay in a superconducting Coulomb-blockaded island
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2015-07-06) Khaymovich, I. M.; Maisi, V. F.; Pekola, J. P.; Mel'nikov, A.S.We show that charge transfer through a small superconducting (S) island of a single-electron transistor is strongly affected by vorticity. This interplay of charge and rotational degrees of freedom in a mesoscopic superconductor occurs through the effect of vorticity on the quantum mechanical spectrum of electron-hole excitations. The subgap quasiparticle levels in vortices can host an extra electron, thus suppressing the so-called parity effect in the S island. We propose to measure the collective dynamics of vorticity and electric charge via the charge pumping effect caused by alternating vortex entry and exit controlled by a periodic magnetic field. - Coupling of zero sound to the real squashing mode in rotating 3He-B
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1989-08-07) Salmelin, R. H.; Pekola, J. P.; Manninen, A. J.; Torizuka, K.; Berglund, M. P.; Kyynäräinen, J. M.; Lounasmaa, O. V.; Tvalashvili, G. K.; Magradze, O. V.; Varoquaux, E.; Avenel, O.; Mineev, V. P.Rotation of superfluid B3 in an magnetic field enhances the coupling of the nonzero mJ substrates of the real squashing collective mode to the zero sound, and the fivefold line splitting becomes observable even when H is parallel to and to the direction of sound propagation. Equilibrium vortex lattices and vortex-free states can be distinguished by their characteristic absorption spectra. The dependence of the sound attenuation on the angular velocity in magnetic fields up to 32 mT is reported; the data are qualitatively compared with theory. - Crossover between Electron-Phonon and Boundary-Resistance Limits to Thermal Relaxation in Copper Films
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-08-23) Wang, L. B.; Saira, O-P; Golubev, D. S.; Pekola, J. P.We observe a crossover fromelectron-phonon (e-ph) coupling limited energy relaxation to that governed by thermal boundary resistance (phonon-phonon coupling, ph-ph) in copper films at subkelvin temperatures. Our measurement yields a quantitative picture of heat currents, in terms of temperature dependences and magnitudes, in both e-ph and pp limited regimes, respectively. We show that by adding a third layer in between the copper film and the substrate, the thermal boundary resistance is increased fourfold, consistent with an assumed series connection of thermal resistances. - Dephasing and dissipation in qubit thermodynamics
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2015-06-08) Pekola, J. P.; Masuyama, Y.; Nakamura, Y.; Bergli, J.; Galperin, Y.M.We analyze the stochastic evolution and dephasing of a qubit within the quantum jump approach. It allows one to treat individual realizations of inelastic processes, and in this way it provides solutions, for instance, to problems in quantum thermodynamics and distributions in statistical mechanics. We demonstrate that dephasing and relaxation of the qubit render the Jarzynski and Crooks fluctuation relations (FRs) of nonequilibrium thermodynamics intact. On the contrary, the standard two-measurement protocol, taking into account only the fluctuations of the internal energy U, leads to deviations in FRs under the same conditions. We relate the average ⟨e−βU⟩ (where β is the inverse temperature) with the qubit's relaxation and dephasing rates in the weak dissipation limit and discuss this relationship for different mechanisms of decoherence. - Detecting parity effect in a superconducting device in the presence of parity switches
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-07-08) Mannila, E. T.; Maisi, V. F.; Nguyen, H. Q.; Marcus, C. M.; Pekola, J. P.We present a superconducting device showing a clear parity effect in the number of electrons, even when there is, on average, a single nonequilibrium quasiparticle present and the parity of the island switches due to quasiparticles tunneling in and out of the device at rates on the order of 100 Hz. We detect the switching by monitoring in real time the charge state of a superconducting island connected to normal leads by tunnel junctions. The quasiparticles are created by Cooper pairs breaking on the island at a rate of a few kilohertz. We demonstrate that the pair breaking is caused by the backaction of the single-electron transistor used as a charge detector. With sufficiently low probing currents, our superconducting island is free of quasiparticles 97% of the time. - Dispersive Thermometry with a Josephson Junction Coupled to a Resonator
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-08-10) Saira, O. -P.; Zgirski, M.; Viisanen, K. L.; Golubev, D. S.; Pekola, J. P.We embed a small Josephson junction in a microwave resonator that allows simultaneous dc biasing and dispersive readout. Thermal fluctuations drive the junction into phase diffusion and induce a temperature-dependent shift in the resonance frequency. By sensing the thermal noise of a remote resistor in this manner, we demonstrate primary thermometry in the range of 300 mK to below 100 mK, and high-bandwidth (7.5 MHz) operation with a noise-equivalent temperature of better than 10 mu K/root Hz. At a finite bias voltage close to a Fiske resonance, amplification of the microwave probe signal is observed. We develop an accurate theoretical model of our device based on the theory of dynamical Coulomb blockade. - Distribution of current fluctuations in a bistable conductor
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-12-27) Singh, S.; Peltonen, Joonas; Khaymovich, I. M.; Koski, J. V.; Flindt, C.; Pekola, J. P.We measure the full distribution of current fluctuations in a single-electron transistor with a controllable bistability. The conductance switches randomly between two levels due to the tunneling of single electrons in a separate single-electron box. The electrical fluctuations are detected over a wide range of time scales and excellent agreement with theoretical predictions is found. For long integration times, the distribution of the time-averaged current obeys the large-deviation principle. We formulate and verify a fluctuation relation for the bistable region of the current distribution. - Electronic structure of a mesoscopic superconducting disk: Quasiparticle tunneling between the giant vortex core and the disk edge
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-04-15) Pekola, J. P.; Samokhvalov, A.; Shereshevskii, I. A.; Vdovicheva, N. K.; Taupin, M.; Khaymovich, I. M.; Mel'nikov, A. S.The electronic structure of the giant vortex states in a mesoscopic superconducting disk is studied in a dirty limit using the Usadel approach. The local density of states profiles are shown to be strongly affected by the effect of quasiparticle (QP) tunneling between the states localized in the vortex core and the ones bound to the sample edge. Decreasing temperature leads to a crossover between the edge-dominated and core-dominated regimes in the magnetic field dependence of the tunneling conductance. This crossover is discussed in the context of the efficiency of quasiparticle cooling by the magnetic-field-induced QP traps in various mesoscopic superconducting devices. - Electrostatic control of quasiparticle poisoning in a hybrid semiconductor-superconductor island
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-07-15) Nguyen, H. Q.; Sabonis, D.; Razmadze, D.; Mannila, E. T.; Maisi, V. F.; van Zanten, D. M.T.; O'Farrell, E. C.T.; Krogstrup, P.; Kuemmeth, F.; Pekola, J. P.; Marcus, C. M.The performance of superconducting devices is often degraded by the uncontrolled appearance and disappearance of quasiparticles, a process known as poisoning. We demonstrate the electrostatic control of quasiparticle poisoning in the form of single-charge tunneling across a fixed barrier onto a Coulomb island in an InAs/Al hybrid nanowire. High-bandwidth charge sensing was used to monitor the charge occupancy of the island across Coulomb blockade peaks, where tunneling rates were maximal, and Coulomb valleys, where tunneling was absent. Electrostatic gates changed the on-peak tunneling rates by two orders of magnitude for a barrier with fixed normal-state resistance, which we attribute to the gate dependence of the size and softness of the induced superconducting gap on the island, corroborated by separate density-of-states measurements. Temperature and magnetic field dependence of tunneling rates are also investigated. - Erratum
Other contribution(2014-10-06) Najafi Jabdaraghi, Robab; Meschke, M.; Pekola, J. P.Applied Physics Letters 105(14), 149903, DOI: http://doi.org/10.1063/1.4897989. Original article: Applied Physics Letters 104, 082601 (2014) - Fast thermometry with a proximity Josephson junction
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-01-01) Wang, L. B.; Saira, O. P.; Pekola, J. P.We couple a proximity Josephson junction to a Joule-heated normal metal film and measure its electron temperature under steady state and nonequilibrium conditions. With a timed sequence of heating and temperature probing pulses, we are able to monitor its electron temperature in nonequilibrium with effectively zero back-action from the temperature measurement in the form of additional dissipation or thermal conductance. The experiments demonstrate the possibility of using a fast proximity Josephson junction thermometer for studying thermal transport in mesoscopic systems and for calorimetry. - Finite-time quantum Stirling heat engine
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-03) Hamedani Raja, S.; Maniscalco, S.; Paraoanu, G. S.; Pekola, J. P.; Lo Gullo, N.We study the thermodynamic performance of a finite-time non-regenerative quantum Stirling-like cycle used as a heat engine. We consider specifically the case in which the working substance (WS) is a two-level system (TLS). The Stirling cycle is made of two isochoric transformations separated by a compression and an expansion stroke during which the WS is in contact with a thermal reservoir. To describe these two strokes we derive a non-Markovian master equation which allows to study the real-time dynamics of a driven open quantum system with arbitrary fast driving. Following the real-time dynamics of the WS using this master equation, the endpoints of the isotherms can deviate from the equilibrium thermal states. The role of this deviation in the performance of the heat engine is addressed. We found that the finite-time dynamics and thermodynamics of the cycle depend non-trivially on the different time scales at play. In particular, driving the WS at a time scale comparable to the resonance time of the bath enhances the performance of the cycle and allows for an efficiency higher than the efficiency of the quasistatic cycle, but still below the Carnot bound. However, by adding thermalization of the WS with the baths at the end of compression/expansion processes one recovers the conventional scenario in which efficiency decreases by speeding up the processes. In addition, the performance of the cycle is dependent on the compression/expansion speeds asymmetrically, which suggests new freedom in optimizing quantum heat engines. The maximum output power and the maximum efficiency are obtained almost simultaneously when the real-time endpoints of the compression/expansion processes are considered instead of the equilibrium thermal endpoint states. However, the net extractable work always declines by speeding up the drive. - First optical observations of superfluid 3He
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1992-10-19) Manninen, A. J.; Pekola, J. P.; Kira, G. M.; Ruutu, J. P.; Babkin, A. V.; Alles, H.; Lounasmaa, O. V.The shape of the free surface of rotating superfluid B3 has been investigated optically. The drastic change in viscosity at the superfluid transition was seen directly. Focusing of light reflected from the liquid surface and expansion of the light beam when it travels through the He3 sample show that the meniscus of the rotating superfluid has the same parabolic shape as that of the normal liquid, which implies an equilibrium density of vortices. The fountain effect in B3 could be seen directly as well: Liquid accumulates into the illuminated region. - Flow of 3He-B through narrow channels
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1982-03) Manninen, M. T.; Pekola, J. P.The critical current Jc of superfluid 3He-B through 0.8-μm-diam channels has been measured. For small currents the pressure difference ΔP=0 along the flow channels within the resolution, implying small or zero dissipation. ΔP grows rapidly with increasing current above Jc; a clear transition to dissipative flow is thus observed. The temperature dependence of Jc indicates that the superfluid density and the critical temperature are reduced inside the narrow flow channels. - Maxwell's demon based on a single qubit
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-01-05) Pekola, J. P.; Golubev, D. S.; Averin, D. V.We propose and analyze Maxwell's demon based on a single qubit with avoided level crossing. Its operation cycle consists of adiabatic drive to the point of minimum energy separation, measurement of the qubit state, and conditional feedback. We show that the heat extracted from the bath at temperature T can ideally approach the Landauer limit of k(B)T ln 2 per cycle even in the quantum regime. Practical demon efficiency is limited by the interplay of Landau-Zener transitions and coupling to the bath. We suggest that an experimental demonstration of the demon is fully feasible using one of the standard superconducting qubits. - Measuring charge-based quantum bits by a superconducting single-electron transistor
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2003-07-30) Kinnunen, J.; Törmä, P.; Pekola, J. P.Single-electron transistors have been proposed to be used as a read-out device for Cooper pair charge qubits. Here we show that a coupled superconducting transistor at a threshold voltage is much more effective in measuring the state of a qubit than a normal-metal transistor at the same voltage range. The effect of the superconducting gap is to almost completely block the current through the transistor when the qubit is in the logical state 1, compared to the mere diminishment of the current in the normal-metal case. The time evolution of the system is solved when the measuring device is driven out of equilibrium, the effect of higher-order contributions is examined and the setting is analyzed numerically for parameters accessible by lithographic aluminum structures. - Model of qubits as devices to detect the third moment of current fluctuations
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2006-07-26) Brosco, Valentina; Fazio, Rosario; Hekking, F. W J; Pekola, J. P.Under appropriate conditions, controllable two-level systems can be used to detect the third moment of current fluctuations. We derive a master equation for a quantum system coupled to a bath valid to the third order in the coupling between the system and the environment. In this approximation the reduced dynamics of the quantum system depends on the frequency-dependent third moment. Specializing to the case of a controllable two-level system (a qubit) and in the limit in which the splitting between the levels is much smaller than the characteristic frequency of the third moment, it is possible to show that the decay of the qubit has additional oscillations whose amplitude is directly proportional to the value of the third moment. We discuss an experimental setup where this effect can be seen.
- «
- 1 (current)
- 2
- 3
- »