Browsing by Author "Pekola, Jukka P."
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Item Absorption refrigerators based on Coulomb-coupled single-electron systems(2018-07-31) Erdman, Paolo Andrea; Bhandari, Bibek; Fazio, Rosario; Pekola, Jukka P.; Taddei, Fabio; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; CNR-ENEA-EURATOM AssociationWe analyze a simple implementation of an absorption refrigerator, a system that requires heat and not work to achieve refrigeration, based on two Coulomb-coupled single-electron systems. We analytically determine the general condition to achieve cooling-by-heating, and we determine the system parameters that simultaneously maximize the cooling power and cooling coefficient of performance (COP) finding that the system displays a particularly simple COP that can reach Carnot's upper limit. We also find that the cooling power can be indirectly determined by measuring a charge current. Analyzing the system as an autonomous Maxwell demon, we find that the highest efficiencies for information creation and consumption can be achieved, and we relate the COP to these efficiencies. Finally, we propose two possible experimental setups based on quantum dots or metallic islands that implement the nontrivial cooling condition. Using realistic parameters, we show that these systems, which resemble existing experimental setups, can develop an observable cooling power.Item Bolometric detection of Josephson inductance in a highly resistive environment(Nature Publishing Group, 2023-12) Subero, Diego; Maillet, Olivier; Golubev, Dmitry S.; Thomas, George; Peltonen, Joonas T.; Karimi, Bayan; Marín-Suárez, Marco; Yeyati, Alfredo Levy; Sánchez, Rafael; Park, Sunghun; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Universidad Autónoma de Madrid; Université Paris-SaclayThe Josephson junction is a building block of quantum circuits. Its behavior, well understood when treated as an isolated entity, is strongly affected by coupling to an electromagnetic environment. In 1983, Schmid predicted that a Josephson junction shunted by a resistance exceeding the resistance quantum R Q = h/4e 2 ≈ 6.45 kΩ for Cooper pairs would become insulating since the phase fluctuations would destroy the coherent Josephson coupling. However, recent microwave measurements have questioned this interpretation. Here, we insert a small Josephson junction in a Johnson-Nyquist-type setup where it is driven by weak current noise arising from thermal fluctuations. Our heat probe minimally perturbs the junction’s equilibrium, shedding light on features not visible in charge transport. We find that the Josephson critical current completely vanishes in DC charge transport measurement, and the junction demonstrates Coulomb blockade in agreement with the theory. Surprisingly, thermal transport measurements show that the Josephson junction acts as an inductor at high frequencies, unambiguously demonstrating that a supercurrent survives despite the Coulomb blockade observed in DC measurements.Item Brownian refrigeration by hybrid tunnel junctions(American Physical Society (APS), 2011) Peltonen, J. T.; Helle, M.; Timofeev, A. V.; Solinas, P.; Hekking, F. W. J.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceVoltage 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.Item Calorimetric measurement of work in a quantum system(IOP Publishing, 2013) Pekola, Jukka P.; Solinas, P.; Shnirman, A.; Averin, D. V.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe propose a calorimetric measurement of work in a quantumsystem. As a physical realization, we consider a superconducting two-levelsystem, a Cooper-pair box, driven by a gate voltage past an avoided levelcrossing at charge degeneracy. We demonstrate that, with realistic experimentalparameters, the temperature measurement of a resistor (environment) can detectsingle microwave photons emitted or absorbed by the two-level system. Thismethod would thus be a way to measure the full distribution of work in repeatedmeasurements, and to assess the quantum fluctuation relations.Item Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscopy imaging(AIP Publishing, 2014) Aref, T.; Averin, A.; van Dijken, Sebastiaan; Ferring, A.; Koberidze, M.; Maisi, V. F.; Nguyend, H. Q.; Nieminen, Risto M.; Pekola, Jukka P.; Yao, L. D.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes.Item Coherent superconducting quantum pump(American Physical Society (APS), 2012) Hoehne, Felix; Pashkin, Yuri A.; Astafiev, Oleg V.; Möttönen, Mikko; Pekola, Jukka P.; Tsai, JawShen; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe demonstrate nonadiabatic charge pumping utilizing a sequence of coherent oscillations between a superconducting island and two reservoirs. The pumping rate for each elementary cycle is limited by the coupling between the island and the reservoirs given by the Josephson energy. Our experimental and theoretical studies show that relaxation can be employed to reset the pump in order to avoid accumulation of errors due to nonideal control pulses. Thus our results demonstrate the effects of nonadiabatic quantum pumping and dissipation.Item Cold electron Josephson transistor(AIP Publishing, 2004) Savin, A. M.; Pekola, Jukka P.; Flyktman, J. T.; Anthore, A.; Giazotto, F.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceA superconductor-normal metal-superconductor mesoscopic Josephson junction has been realized in which the critical current is tuned through normal current injection using a symmetric electron cooler directly connected to the weak link. Both enhancement of the critical current by more than a factor of two, and supercurrent suppression have been achieved by varying the cooler bias. Furthermore, this transistor-like device demonstrates large current gain (∼20) and low power dissipation.Item Colloquium: Quantum heat transport in condensed matter systems(American Physical Society, 2021-10-05) Pekola, Jukka P.; Karimi, Bayan; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and DevicesIn this Colloquium recent advances in the field of quantum heat transport are reviewed. This topic has been investigated theoretically for several decades, but only during the past 20 years have experiments on various mesoscopic systems become feasible. A summary of the theoretical basis for describing heat transport in one-dimensional channels is first provided. The main experimental investigations of quantized heat conductance due to phonons, photons, electrons, and anyons in such channels are then presented. These experiments are important for understanding the fundamental processes that underlie the concept of a heat conductance quantum for a single channel. An illustration of how one can control the quantum heat transport by means of electric and magnetic fields, and how such tunable heat currents can be useful in devices, is first given. This lays the basis for realizing various thermal device components such as quantum heat valves, rectifiers, heat engines, refrigerators, and calorimeters. Also of interest are fluctuations of quantum heat currents, both for fundamental reasons and for optimizing the most sensitive thermal detectors; at the end of the Colloquium the status of research on this topic is given.Item Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of Liquid 3He below 10 mK(American Physical Society (APS), 1981) Lhota, E.; Manninen, M. T.; Pekola, Jukka P.; Soinne, A. T.; Soulen, R. J.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceThe Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid 3He (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear-orientation temperature scale. The superfluid transition temperature (Tc) of 3He at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. Tc on the NBS scale was found to be 1.025 ± 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of 3He.Item Cooled video camera for optical investigations below 1 mK(AIP Publishing, 1994) Alles, H.; Ruutu, J. P.; Babkin, A. V.; Hakonen, Pertti J.; Manninen, A. J.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceAn optical imaging system for milliKelvin temperatures has been developed based on a regular B/W surveillance camera (25 frames/s), with its CCD sensor inside the 4‐K vacuum can of our nuclear demagnetization cryostat. The heat leak to the nuclear stage, caused by the operation of the video camera, was reduced below 1 nW by careful rf shielding. The construction of the system and its limits of operation are discussed.Item Cooper-Pair Box Coupled to Two Resonators: An Architecture for a Quantum Refrigerator(American Physical Society, 2022-06) Guthrie, Andrew; Satrya, Christoforus Dimas; Chang, Yu Cheng; Menczel, Paul; Nori, Franco; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; RIKENSuperconducting circuits present a promising platform with which to realize a quantum refrigerator. Motivated by this, we fabricate and perform spectroscopy of a gated Cooper-pair box, capacitively coupled to two superconducting coplanar-waveguide resonators with different frequencies. We experimentally demonstrate the strong coupling of a charge qubit to two superconducting resonators, with the ability to perform voltage driving of the qubit at gigahertz frequencies. We go on to discuss how the measured device could be modified to operate as a cyclic quantum refrigerator by terminating the resonators with normal-metal resistors acting as heat baths.Item Cooper-pair current in the presence of flux noise(2012-01-20) Solinas, Paolo; Möttonen, Mikko; Salmilehto, J.; Pekola, Jukka P.; Department of Applied PhysicsWe study the effect of flux noise on the Cooper pair current of a superconducting charge pump. We generalize the definition of the current in order to take into account the contribution induced by the environment. It turns out that this dissipative current vanishes for charge noise but it is finite in general for noise operators that do not commute with the charge operator. We discuss in a generic framework the effect of flux noise and present a way to engineer it by coupling the system to an additional external circuit. We calculate numerically the pumped charge through the device by solving the master equation for the reduced density matrix of the system and show how it depends on the coupling to the artificial environment.Item Cooper-pair current in the presence of flux noise(American Physical Society (APS), 2012) Solinas, P.; Möttönen, M.; Salmilehto, J.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe study the effect of flux noise on the Cooper pair current of a superconducting charge pump. We generalize the definition of the current in order to take into account the contribution induced by the environment. It turns out that this dissipative current vanishes for charge noise but it is finite in general for noise operators that do not commute with the charge operator. We discuss in a generic framework the effect of flux noise and present a way to engineer it by coupling the system to an additional external circuit. We calculate numerically the pumped charge through the device by solving the master equation for the reduced density matrix of the system and show how it depends on the coupling to the artificial environment.Item Correlated versus uncorrelated noise acting on a quantum refrigerator(2017-09-05) Karimi, Bayan; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and DevicesTwo qubits form a quantum four-level system. The golden-rule based transition rates between these states are determined by the coupling of the qubits to noise sources. We demonstrate that depending on whether the noise acting on the two qubits is correlated or not, these transitions are governed by different selection rules. In particular, we find that for fully correlated or anticorrelated noise, there is a protected state, and the dynamics of the system depends then on its initialization. For nearly (anti)correlated noise, there is a long time scale determining the temporal evolution of the qubits. We apply our results to a quantum Otto refrigerator based on two qubits coupled to hot and cold baths. The steady-state power does not scale with the number (=2 here) of the qubits when there is a strong correlation of noise acting on them; under driven conditions the highest cooling power of the refrigerator is achieved for fully uncorrelated baths.Item Coupling of zero sound to the real squashing mode in rotating 3B(American Physical Society (APS), 1989) Salmelin, Riitta; Pekola, Jukka 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.; Department of Neuroscience and Biomedical Engineering; Neurotieteen ja lääketieteellisen tekniikan laitos; Perustieteiden korkeakoulu; School of ScienceRotation of superfluid 3B 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 Ω 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.Item Critical current of 3He-A in narrow channels(American Physical Society (APS), 1982) Manninen, M. T.; Pekola, Jukka P.; Sharma, R. G.; Tagirov, M. S.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceThe critical current Jc of superfluid 3He-A in 0.8-μm-diam channels has been measured by the observation of the pressure difference along the channels versus the mass current. During warming Jc was found to decrease by about 30% at TBA(cyl) and by another 30% at TBA; TBA(cyl) is the reduced B→A transition temperature in the narrow flow channels, with TBA(cyl)TBA=0.92 at 27.4 bars. Above TBA a second dissipative mechanism was observed at lower currents. These features are believed to be associated with the ends of the channels.Item Critical flow and persistent current experiments in superfluid [sup 3]He(Helsinki University of Technology, 1984) Pekola, Jukka P.; Packard, Richard; Manninen, Mikko; O.V. Lounasmaa -laboratorio; O.V. Lounasmaa Laboratory; Perustieteiden korkeakoulu; School of ScienceItem Decoherence in Adiabatic Quantum Evolution: Application to Cooper Pair Pumping(American Physical Society (APS), 2010) Pekola, Jukka P.; Brosco, V.; Möttönen, M.; Solinas, P.; Shnirman, A.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceOne of the challenges of adiabatic control theory is the proper inclusion of the effects of dissipation. Here we study the adiabatic dynamics of an open two-level quantum system deriving a generalized master equation to consistently account for the combined action of the driving and dissipation. We demonstrate that in the zero-temperature limit the ground state dynamics is not affected by environment. As an example, we apply our theory to Cooper pair pumping, which demonstrates the robustness of ground state adiabatic evolution.Item Decoherence of adiabatically steered quantum systems(American Physical Society (APS), 2010) Solinas, P.; Möttönen, M.; Salmilehto, J.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe study the effect of Markovian environmental noise on the dynamics of a two-level quantum system which is steered adiabatically by an external driving field. We express the master equation taking consistently into account all the contributions to the lowest nonvanishing order in the coupling to the Markovian environment. We study the master equation numerically and analytically and we find that, in the adiabatic limit, a zero-temperature environment does not affect the ground-state evolution. As a physical application, we discuss extensively how the environment affects Cooper-pair pumping. The adiabatic ground-state pumping appears to be robust against environmental noise. In fact, the relaxation due to the environment is required to avoid the accumulation of small errors from each pumping cycle. We show that neglecting the nonsecular terms in the master equation leads to unphysical results, such as charge nonconservation. We discuss also a possible way to control the environmental noise in a realistic physical setup and its influence on the pumping process.Item Detection of mechanical resonance of a single-electron transistor by direct current(AIP Publishing, 2010) Pashkin, Yu. A.; Li, T. F.; Pekola, Jukka P.; Astafiev, O.; Knyazev, D. A.; Hoehne, F.; Im, H.; Nakamura, Y.; Tsai, J. S.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe have suspended an Al based single-electron transistor (SET) whose island can resonate freely between the source and drain leads forming the clamps. In addition to the regular side gate, a bottom gate with a larger capacitance to the SET island is placed underneath to increase the SET coupling to mechanical motion. The device can be considered as a doubly clamped Al beam that can transduce mechanical vibrations into variations in the SET current. Our simulations based on the orthodox model, with the SET parameters estimated from the experiment, reproduce the observed transport characteristics in detail.