Browsing by Author "Saira, Olli-Pentti"
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Item Development of a lumped element Josephson parametric amplifier for frequencies below 1 GHz(2015-05-12) Räisänen, Ilmo; Saira, Olli-Pentti; Perustieteiden korkeakoulu; Pekola, JukkaIt is important to measure temperature fast and accurately in many experiments in low-temperature physics and nanophysics. The accuracy of the measurement is compromised by noise. A Josephson parametric amplifier (JPA) can provide us with low-noise amplification in the microwave frequency range (300 MHz - 30 GHz) for, e.g., radio frequency thermometry and radiation detection. This Master's thesis presents a lumped element JPA made in collaboration by Aalto University and VTT and reports its refection coefficient, gain, bandwidth, 1 dB compression point, noise temperature and quality factors. Experimental results are compared with nonlinear circuit simulations done with APLAC, which gives us information about component properties for fabrication of a new device. Reflection coefficient measurement gives us the resonance frequency (642.0 MHz) and the bifurcation frequency (640.2 MHz) of the JPA. Gain measurement reveals the maximal gain (26.2 dB), the optimal operating frequency (641.3 MHz) and the optimal pump power (-96 dBm). The gain-bandwidth product is simulated as a function of coupling capacitance and pump power and it is observed to be lower than what theory suggests. The noise temperature of the JPA is measured to be between 1 K and 4 K in thefrequency range 639.25 MHz ... 640.45 MHz according to both the Y-factor method and the signal-to-noise ratio (SNR) method, but according to the SNR method the noise temperature is roughly 50 % lower than according to the Y-factor method. When the pump generator is off, the noise temperature of the system is between 25 K and 80 K in the frequency range 639.15 MHz ... 640.30 MHz according to the SNR method.Item Electrostatic control of quasiparticle transport in superconducting hybrid nanostructures(Aalto University, 2013) Saira, Olli-Pentti; Möttönen, Mikko, Dr.Tech., Aalto University, Finland; O.V. Lounasmaa -laboratorio; O.V. Lounasmaa Laboratory; PICO group; Perustieteiden korkeakoulu; School of Science; Pekola, Jukka, Prof., Aalto University, FinlandA flow of electric current in a metal is the result of the collective motion of mobile conduction electrons within a relatively static background formed by ionized atoms. An electric current of 1 ampere used in everyday appliances corresponds to a flow rate of about 6*1018 electrons per second. In this thesis, I have studied experimentally and theoretically certain metallic nanostructures where electric charge can be measured and transported at a precision of one electron. Before this thesis, single-electron effects in hybrid structures consisting of superconductors (S) and normal metals (N) had not been thoroughly investigated. Many of the new results presented in this thesis concern the SINIS-type single-electron transistor. This structure consists of superconducting source and drain electrodes with a normal metallic island in between. The island is contacted to the electrodes via tunnel junctions (I). Due to a phenomenon konwn as the Coulomb blockade, the electric and heat currents through the transistor can be significantly altered by changing the gate charge by a fraction of the elementary charge. Several physical phenomena in the SINIS transistor were observed for the first time in the experiments of this thesis: We showed that the cooling power incident on the normal metal of the transistor can be modulated by the gate charge. We also demonstrated that the SINIS transistor can be used as an electron turnstile. The electric current through the turnstile is equal to the product of the elementary charge and the frequency of an external driving signal. A device that realizes this current-frequency-dependence with a sufficiently high accuracy could be used in electrical metrology in the future. As an important technological advance in the study of hybrid structures, we demonstrate that single-electron tunneling events between a superconductor and a normal metal can be detected in real time with a capacitively coupled single-electron transistor. By counting individual electrons, electric currents less than 1 attoampere can be measured, which is impossible with traditional room-temperature electronics. By measuring the rate of electron tunneling events, we were able to study the coupling of high frequency microwaves and so-called nonequilibrium quasiparticles to the measured samples. Finally, we have determined the distribution of heat dissipated in the process of charging a metallic island by a single electron.Item Environmentally activated tunneling events in a hybrid single-electron box(2010-10-26) Saira, Olli-Pentti; Möttönen, Mikko; Maisi, Ville; Pekola, Jukka P.; Department of Applied Physics; Quantum Computing and DevicesWe have measured individual tunneling events and Coulomb step shapes in single-electron boxes with opaque superconductor–normal metal tunnel junctions. We observe anomalous broadening of the Coulomb step with decreasing temperature in a manner that is consistent with activation of first-order tunneling events by an external dissipative electromagnetic environment. We demonstrate that the rates for energetically unfavorable tunneling events saturate to finite values at low temperatures, and that the saturation level can be suppressed by more than an order of magnitude by a capacitive shunt near the device. The findings are important in assessing the performance limits of any single-electronic device. In particular, master-equation-based simulations show that the electromagnetic environment realized in the capacitively shunted devices allows for a metrologically accurate charge pump based on hybrid tunnel junctions.Item Fast Electron Thermometry for Ultrasensitive Calorimetric Detection(2015) Gasparinetti, S.; Viisanen, Klaara; Saira, Olli-Pentti; Faivre, T.; Arzeo, M.; Meschke, M.; Pekola, J.P.; Quantum Phenomena and Devices; Department of Applied PhysicsWe 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.Item Heat Transistor: Demonstration of Gate-Controlled Electronic Refrigeration(American Physical Society (APS), 2007) Saira, Olli-Pentti; Meschke, Matthias; Giazotto, Francesco; Savin, Alexander M.; Möttönen, Mikko; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe present experiments on a superconductor–normal-metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor; i.e., the heat flux out from the normal-metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system.Item Heat transistor: Demonstration of gate-controlled electronic refrigeration(2007-07-09) Saira, Olli-Pentti; Meschke, Matthias; Giazotto, Francesco; Savin, Alexander; Möttönen, Mikko; Pekola, Jukka; Department of Applied PhysicsWe present experiments on a superconductor–normal-metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor; i.e., the heat flux out from the normal-metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system.Item Incomplete measurement of work in a dissipative two level system(2015-05-13) Viisanen, Klaara; Suomela, S.; Gasparinetti, S.; Saira, Olli-Pentti; Ankerhold, Joachim; Pekola, Jukka; Department of Applied PhysicsWe discuss work performed on a quantum two-level system coupled to multiple thermal baths. To evaluate the work, a measurement of photon exchange between the system and the baths is envisioned. In a realistic scenario, some photons remain unrecorded as they are exchanged with baths that are not accessible to the measurement, and thus only partial information on work and heat is available. The incompleteness of the measurement leads to substantial deviations from standard fluctuation relations. We propose a recovery of these relations, based on including the mutual information given by the counting efficiency of the partial measurement. We further present the experimental status of a possible implementation of the proposed scheme, i.e. a calorimetric measurement of work, currently with nearly single-photon sensitivity.Item Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces(2016-01-25) Najafi Jabdaraghi, Robab; Peltonen, Joonas; Saira, Olli-Pentti; Pekola, Jukka; Department of Applied PhysicsWe characterize niobium-based lateral Superconductor (S)-Normal metal (N)-Superconductor (SNS) weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that have contacted with evaporated Cu. The two-step fabrication flow enables more flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. We further demonstrate a hybrid magnetic flux sensor based on an Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.Item Multifractality of random eigenfunctions and generalization of Jarzynski equality(2015-04-27) Khaymovich, Ivan; Koski, Jonne; Saira, Olli-Pentti; Kravtsov, V.E.; Pekola, Jukka; Department of Applied PhysicsSystems driven out of equilibrium experience large fluctuations of the dissipated work. The same is true for wavefunction amplitudes in disordered systems close to the Anderson localization transition. In both cases, the probability distribution function is given by the large-deviation ansatz. Here we exploit the analogy between the statistics of work dissipated in a driven single-electron box and that of random multifractal wavefunction amplitudes, and uncover new relations that generalize the Jarzynski equality. We checked the new relations theoretically using the rate equations for sequential tunnelling of electrons and experimentally by measuring the dissipated work in a driven single-electron box and found a remarkable correspondence. The results represent an important universal feature of the work statistics in systems out of equilibrium and help to understand the nature of the symmetry of multifractal exponents in the theory of Anderson localization.Item Nanobolometer with ultralow noise equivalent power(NATURE PUBLISHING GROUP, 2019-10-11) Kokkoniemi, Roope; Govenius, Joonas; Vesterinen, Visa; Lake, Russell E.; Gunyho, Andras M.; Tan, Kuan Y.; Simbierowicz, Slawomir; Gronberg, Leif; Lehtinen, Janne; Prunnila, Mika; Hassel, Juha; Lamminen, Antti; Saira, Olli-Pentti; Mottonen, Mikko; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Computing and Devices; VTT Technical Research Centre of FinlandSince the introduction of bolometers more than a century ago, they have been used in various applications ranging from chemical sensors, consumer electronics, and security to particle physics and astronomy. However, faster bolometers with lower noise are of great interest from the fundamental point of view and to find new use-cases for this versatile concept. We demonstrate a nanobolometer that exhibits roughly an order of magnitude lower noise equivalent power, 20zW/root Hzp, than previously reported for any bolometer. Importantly, it is more than an order of magnitude faster than other low-noise bolometers, with a time constant of 30 mu s at 60zW/root Hzp. These results suggest a calorimetric energy resolution of 0.3 zJ = h x 0.4 THz with a time constant of 30 mu s. Further development of this nanobolometer may render it a promising candidate for future applications requiring extremely low noise and high speed such as those in quantum technology and terahertz photon counting.Item Radio-Frequency Single-Electron Refrigerator(American Physical Society (APS), 2007) Pekola, Jukka P.; Giazotto, Francesco; Saira, Olli-Pentti; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of ∼kBT×f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of ∼kBT/Δ, where Δ is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.Item Radio-frequency single-electron refrigerator(2007-01-16) Pekola, Jukka; Giazotto, Francesco; Saira, Olli-Pentti; Department of Applied PhysicsWe propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of ∼kBT×f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of ∼kBT/Δ, where Δ is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.Item Single-charge escape processes through a hybrid turnstile in a dissipative environment(IOP Publishing, 2011) Lotkhov, Sergey V.; Saira, Olli-Pentti; Pekola, Jukka P.; Zorin, Alexander B.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe have investigated the static, charge-trapping properties of a hybrid superconductor–normal metal electron turnstile embedded in a high-ohmic environment. The device includes a local Cr resistor on one side of the turnstile, and a superconducting trapping island on the other side. The electron hold times, τ~2–20 s, in our two-junction circuit are comparable with those of typical multi-junction, N≥4, normal-metal single-electron tunneling devices. A semi-phenomenological model of the environmental activation of tunneling is applied for the analysis of the switching statistics. The experimental results are promising for electrical metrology applications.Item Single-electron current sources: Toward a refined definition of the ampere(American Physical Society (APS), 2013) Pekola, Jukka P.; Saira, Olli-Pentti; Maisi, Ville F.; Kemppinen, Antti; Möttönen, Mikko; Pashkin, Yuri A.; Averin, Dmitri V.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceThe control of electrons at the level of the elementary charge e was demonstrated experimentally already in the 1980s. Ever since, the production of an electrical current ef, or its integer multiple, at a drive frequency f has been a focus of research for metrological purposes. This review discusses the generic physical phenomena and technical constraints that influence single-electron charge transport and presents a broad variety of proposed realizations. Some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently “just” wild ideas, still often potentially competitive if technical constraints can be lifted. The important issues of readout of single-electron events and potential error correction schemes based on them are also discussed. Finally, an account is given of the status of single-electron current sources in the bigger framework of electric quantum standards and of the future international SI system of units, and applications and uses of single-electron devices outside the metrological context are briefly discussed.Item Thermal effects in Coulomb-blockaded nanostructures with superconductor-insulator-normal metal junctions(2007) Saira, Olli-Pentti; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Kaivola, MattiSuprajohde-eriste-normaalimetalli (SIN) -tyypin tunneliliitoksia voidaan käyttää elektronijäähdyttiminä tai herkkinä normaalimetallin elektronilämpötilan antureina. Modernilla valmistustekniikalla voidaan puolestaan toteuttaa nanorakenteita, joissa sähkövarauksen kuljetus on mahdollista yksittäisten elektronien tarkkuudella Coulombin saarroksi kutsutun ilmiön avulla. Tässä työssä tutkitaan Coulomb- saarrettujen SINIS- rakenteiden sähköisiä ja termisiä ominaisuuksia. Työssä esitetty teoreettinen analyysi perustuu niin sanottuun yksielektronitunneloinnin ortodoksiteoriaan. Työn kokeellista osuutta varten valmistettiin elektronisuihkulitografiaa ja monikulmahöyrystystä käyttäen SINIS- näytteitä, joiden tunneliliitokset olivat kooltaan alle 100 nm x 100 nm. Mittaukset tehtiin 3He-4He-diluutiokryostaatissa alle 500 mK lämpötiloissa. Tämän diplomityön keskeisin kokeellinen tulos on lämpötransistoriksi nimetyn Coulomb- saarretun SINIS- rakenteen jäähdytystehon hilajännitemodulaation havaitseminen. Tähän läheisesti liittyvä tulos on Coulomb- saarretun normaalimetallisaarekkeen elektronilämpötilan määrittäminen SIN- liitoksen kvasipartikkelivirran avulla. Kokeelliset havainnot vastaavat teoreettisia ennusteita erittäin hyvin. Lisäksi työssä analysoidaan samaa teoreettista mallia käyttäen kahta muuta Coulomb- saarretun SINIS- rakenteen käyttötapaa. Kun rakennetta käytetään ilman esijännitettä ja hilaan kohdistetaan radiotaajuinen signaali, saadaan aikaan taajuuteen verrannollinen jäähdytysteho. Sopivalla nollasta poikkeavalla esijännitteellä laite toimii tarkkana sähkövirran kääntöporttina, millä voi olla metrologisia sovelluksia.Item Tunnel junction thermometry down to millikelvin temperatures(2015-09-03) Feshchenko, Anna; Casparis, L.; Khaymovich, Ivan; Maradan, D.; Saira, Olli-Pentti; Palma, M.; Meschke, M.; Pekola, Jukka; Zumbühl, D.M.; Department of Applied PhysicsWe present a simple on-chip electronic thermometer with the potential to operate down to 1 mK. It is based on transport through a single normal-metal–superconductor tunnel junction with rapidly widening leads. The current through the junction is determined by the temperature of the normal electrode that is efficiently thermalized to the phonon bath, and it is virtually insensitive to the temperature of the superconductor, even when the latter is relatively far from equilibrium. We demonstrate here the operation of the device down to 7 mK and present a systematic thermal analysis.
