### Browsing by Department "Quantum Phenomena and Devices"

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Item Active Quasiparticle Suppression in a Non-Equilibrium Superconductor(AMERICAN CHEMICAL SOCIETY, 2020-07-08) Marin Suarez, Marco; Peltonen, Joonas; Pekola, J.P.; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsQuasiparticle (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.Item Control of the surface plasmon dispersion and Purcell effect at the metamaterial-dielectric interface(Nature Publishing Group, 2020-11-30) Ivanov, Konstantin A.; Morozov, Konstantin M.; Pozina, Galia; Gubaydullin, Azat R.; Girshova, Elizaveta I.; Kaliteevski, Mikhail A.; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO); Linköping University; Quantum Phenomena and Devices; Department of Applied PhysicsThe use of metamaterial as a way to mitigate the negative effects of absorption in metals on the Purcell effect in metal-dielectric structures is investigated. A layered metal-dielectric structure is considered as an anisotropic medium in the long-wavelength limit. The dispersion of the surface plasmon appearing at the boundary between such a structure and a different dielectric material, as well as the position of the peak in the local density of states are studied for various combinations of materials and filling factors of the periodic structure. The calculated frequency dependence of the Purcell factor demonstrates an increase in peak value compared to the conventional plasmonic structure. The results obtained using effective media approach are compared to the results of numerical modelling.Item Correlated versus uncorrelated noise acting on a quantum refrigerator(2017-09-05) Karimi, Bayan; Pekola, Jukka P.; Quantum Phenomena and Devices; Department of Applied PhysicsTwo 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 Determining the parameters of a random telegraph signal by digital low pass filtering(2018-06-11) Singh, Shilpi; Mannila, Elsa T.; Golubev, Dmitry S.; Peltonen, Joonas T.; Pekola, Jukka P.; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsWe propose a method to determine the switching rates of a random telegraph signal. We apply digital low pass filtering with varying bandwidths to the raw signal, evaluate the cumulants of the resulting distributions, and compare them with the analytical prediction. This technique is useful in the case of a slow detector with response time comparable to the time interval between the switching events. We demonstrate the efficiency of this method by analyzing random telegraph signals generated by individual charge tunneling events in metallic single-electron transistors.Item Electromagnetic simulation and microwave circuit approach of heat transport in superconducting qubits(Institute of Physics Publishing, 2023-02-23) Satrya, Christoforus Dimas; Guthrie, Andrew; Mäkinen, Ilari K.; Pekola, Jukka P.; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied Physics; Department of Applied PhysicsThe study of quantum heat transport in superconducting circuits is significant for further understanding the connection between quantum mechanics and thermodynamics, and for possible applications for quantum information. The first experimental realisations of devices demonstrating photonic heat transport mediated by a qubit have already been designed and measured. Motivated by the analysis of such experimental results, and for future experimental designs, we numerically evaluate the photonic heat transport of qubit-resonator devices in the linear circuit regime through electromagnetic simulations using Sonnet software, and compare with microwave circuit theory. We show that the method is a powerful tool to calculate heat transport and predict unwanted parasitic resonances and background.Item An electron turnstile for frequency-to-power conversion(Nature Publishing Group, 2022-03) Marín-Suárez, Marco; Peltonen, Joonas T.; Golubev, Dmitry S.; Pekola, Jukka P.; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsSingle-electron transport relates an operation frequency f to the emitted current I through the electron charge e as I = ef (refs. 1–5). Similarly, direct frequency-to-power conversion (FPC) links both quantities through a known energy. FPC is a natural candidate for a power standard resorting to the most basic definition of the watt: energy emitted per unit of time. The energy is traceable to Planck’s constant and the time is in turn traceable to the unperturbed ground state hyperfine transition frequency of the caesium 133 atom. Hence, FPC comprises a simple and elegant way to realize the watt6. In this spirit, single-photon emission7,8 and detection9 at known rates have been proposed as radiometric standards and experimentally realized10–14. However, power standards are so far only traceable to electrical units, that is, to the volt and the ohm6,15–17. In this Letter, we demonstrate an alternative proposal based on solid-state direct FPC using a hybrid single-electron transistor (SET). The SET injects n (integer) quasi-particles (QPs) per cycle into the two superconducting leads with discrete energies close to their superconducting gap Δ, even at zero source-drain voltage. Furthermore, the application of a bias voltage can vary the distribution of the power among the two leads, allowing for an almost equal power injection nΔf into the two. While in single-electron transport current is related to a fixed universal constant (e), in our approach Δ is a material-dependent quantity. We estimate that under optimized conditions errors can be well below 1%.Item Electron-phonon coupling of epigraphene at millikelvin temperatures measured by quantum transport thermometry(AMER INST PHYSICS, 2021-03-08) Karimi, Bayan; He, Hans; Chang, Yu Cheng; Wang, Libin; Pekola, Jukka P.; Yakimova, Rositsa; Shetty, Naveen; Peltonen, Joonas T.; Lara-Avila, Samuel; Kubatkin, Sergey; Centre of Excellence in Quantum Technology, QTF; Chalmers University of Technology; Department of Applied Physics; Linköping University; Quantum Phenomena and DevicesWe investigate the basic charge and heat transport properties of charge neutral epigraphene at sub-kelvin temperatures, demonstrating a nearly logarithmic dependence of electrical conductivity over more than two decades in temperature. Using graphene's sheet conductance as an in situ thermometer, we present a measurement of electron-phonon heat transport at mK temperatures and show that it obeys the T4 dependence characteristic for a clean two-dimensional conductor. Based on our measurement, we predict the noise-equivalent power of ∼ 10 - 22 W / Hz of the epigraphene bolometer at the low end of achievable temperatures.Item Electrostatic control of quasiparticle poisoning in a hybrid semiconductor-superconductor island(American Physical Society, 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.; Niels Bohr Institute; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsThe 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.Item 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.; O.V.Lounasmaa-laboratorio; Quantum Phenomena and DevicesWe 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.Item Fast and accurate Cooper pair pump(American Physical Society, 2019-12-16) Erdman, Paolo A.; Taddei, Fabio; Peltonen, Joonas T.; Fazio, Rosario; Pekola, Jukka P.; Scuola Normale Superiore di Pisa; Consiglio Nazionale delle Ricerche (CNR); Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsWe propose a method to perform accurate and fast charge pumping in superconducting nanocircuits. Combining topological properties and quantum control techniques based on shortcuts to adiabaticity, we show that it is theoretically possible to achieve perfectly quantized charge pumping at any finite-speed driving. Model-specific errors may still arise due the difficulty of implementing the exact control. We thus assess this and other practical issues in a specific system comprised of three Josephson junctions. Using realistic system parameters, we show that our scheme can improve the pumping accuracy of this device by various orders of magnitude. Possible metrological perspectives are discussed.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 Full Counting Statistics of Andreev Tunneling(2014-01-23) Maisi, Ville; Kambly, Dania; Flindt, Christian; Pekola, Jukka P.; Quantum Phenomena and Devices; University of Geneva; O.V.Lounasmaa-laboratorioWe employ a single-charge counting technique to measure the full counting statistics of Andreev events in which Cooper pairs are either produced from electrons that are reflected as holes at a superconductor–normal-metal interface or annihilated in the reverse process. The full counting statistics consists of quiet periods with no Andreev processes, interrupted by the tunneling of a single electron that triggers an avalanche of Andreev events giving rise to strongly super-Poissonian distributions.Item A Josephson radiation comb generator(2015) Solinas, P.; Gasparinetti, S.; Golubev, D.; Giazotto, F.; Quantum Phenomena and Devices; Department of Applied PhysicsWe propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrologyto sub-millimeter wave generation.Item Joule heating effects in high-Transparency Josephson junctions(American Physical Society, 2021-10-21) Tomi, Matti; Samatov, Mikhail R.; Vasenko, Andrey S.; Laitinen, Antti; Hakonen, Pertti; Golubev, Dmitry S.; Centre of Excellence in Quantum Technology, QTF; Higher School of Economics; Quantum Phenomena and Devices; Department of Applied PhysicsWe study, both theoretically and experimentally, the features on the current-voltage characteristic of a highly transparent Josephson junction caused by transition of the superconducting leads to the normal state. These features appear due to the suppression of the Andreev excess current. We show that by tracing the dependence of the voltage, at which the transition occurs, on the bath temperature and by analyzing the suppression of the excess current by the bias voltage one can recover the temperature dependence of the heat flow out of the junction. We verify theory predictions by fabricating two highly transparent superconductor-graphene-superconductor (SGS) Josephson junctions with suspended and nonsuspended graphene as a nonsuperconducting section between Al leads. Applying the above mentioned technique we show that the cooling power of the suspended junction depends on the bath temperature as â Tbath3.1 close to the superconducting critical temperature.Item Learning to Measure: Adaptive Informationally Complete Generalized Measurements for Quantum Algorithms(American Physical Society, 2021-11-29) Garcia-Perez, Guillermo; Rossi, Matteo A. C.; Sokolov, Boris; Tacchino, Francesco; Barkoutsos, Panagiotis Kl; Mazzola, Guglielmo; Tavernelli, Ivano; Maniscalco, Sabrina; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsMany prominent quantum computing algorithms with applications in fields such as chemistry and materials science require a large number of measurements, which represents an important roadblock for future real-world use cases. We introduce a novel approach to tackle this problem through an adaptive measurement scheme. We present an algorithm that optimizes informationally complete positive operator-valued measurements (POVMs) on the fly in order to minimize the statistical fluctuations in the estimation of relevant cost functions. We show its advantage by improving the efficiency of the variational quantum eigensolver in calculating ground-state energies of molecular Hamiltonians with extensive numerical simulations. Our results indicate that the proposed method is competitive with state-of-the-art measurement-reduction approaches in terms of efficiency. In addition, the informational completeness of the approach offers a crucial advantage, as the measurement data can be reused to infer other quantities of interest. We demonstrate the feasibility of this prospect by reusing ground-state energy-estimation data to perform high-fidelity reduced state tomography.Item Low Temperature Characteristics of the Metal–Superconductor NIS Tunneling Thermometer(SPRINGER/PLENUM PUBLISHERS, 2022-05) Karimi, Bayan; Chang, Yu Cheng; Pekola, Jukka P.; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsWe discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.Item Optimized proximity thermometer for ultrasensitive detection : Role of an ohmic electromagnetic environment(American Physical Society, 2023-07-01) Nikolić, Danilo; Karimi, Bayan; Rengel, Diego Subero; Pekola, Jukka P.; Belzig, Wolfgang; Universität Konstanz; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsWe propose a mesoscopic thermometer for ultrasensitive detection based on the proximity effect in superconductor-normal metal (SN) heterostructures. The device is based on the zero-bias anomaly due to the inelastic Cooper-pair tunneling in an SNIS junction (I stands for an insulator) coupled to an ohmic electromagnetic (EM) environment. The theoretical model is done in the framework of the quasiclassical Usadel Green's formalism and the dynamical Coulomb blockade. The usage of an ohmic EM environment makes the thermometer highly sensitive down to very low temperatures, Formula Presented. Moreover, defined in this way, the thermometer is stable against small but nonvanishing voltage amplitudes typically used for measuring the zero-bias differential conductance in experiments. Finally, we propose a simplified view, based on an analytic treatment, which is in very good agreement with numerical results and can serve as a tool for the development, calibration, and optimization of such devices in future experimentsin quantum calorimetry.Item Photonic heat transport across a Josephson junction(American Physical Society, 2019-09-05) Thomas, George; Pekola, Jukka P.; Golubel, Dmitry S.; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsWe present a detailed study of photonic heat transport across a Josephson junction coupled to two arbitrary linear circuits having different temperatures. First, we consider the linear approximation, in which a nonlinear Josephson potential is replaced by a quadratic one and the junction acts as an inductor. Afterwards, we discuss the effects of junction anharmonicity. We separately consider the weak-coupling limit, in which the Bloch band structure of the junction energy spectrum plays an important role, and the opposite strong-coupling regime. We apply our general results to two specific models: a Josephson junction coupled to two Ohmic resistors and two resonators. We derive simple analytical approximations for the photonic heat flux in many limiting cases. We demonstrate that electric circuits with embedded Josephson junctions provide a useful platform for quantum thermodynamics experiments.Item Photonic heat transport from weak to strong coupling(American Physical Society, 2023-03-01) Tam, Minh; Thomas, George; Golubev, Dmitry S.; Aalto University; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsSuperconducting circuits provide a favorable platform for quantum thermodynamic experiments. An important component for such experiments is a heat valve, i.e., a device which allows one to control the heat power flowing through the system. Here we theoretically study the heat valve based on a superconducting quantum interference device (SQUID) coupled to two heat baths via two resonators. The heat current in such a system can be tuned by magnetic flux. We investigate how the heat current modulation depends on the coupling strength g between the SQUID and the resonators. In the weak coupling regime the heat current modulation grows as g2, but, surprisingly, at the intermediate coupling it can be strongly suppressed. This effect is linked to the resonant nature of the heat transport at weak coupling, where the heat current dependence on the magnetic flux is a periodic set of narrow peaks. At the intermediate coupling the peaks become broader and overlap, thus reducing the heat modulation. At very strong coupling the heat modulation grows again and finally saturates at a constant value.Item Photonic heat transport in three terminal superconducting circuit(Nature Publishing Group, 2022-03-23) Gubaydullin, Azat; Thomas, George; Golubev, Dmitry S.; Lvov, Dmitrii; Peltonen, Joonas T.; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTFWe report an experimental realization of a three-terminal photonic heat transport device based on a superconducting quantum circuit. The central element of the device is a flux qubit made of a superconducting loop containing three Josephson junctions, which can be tuned by magnetic flux. It is connected to three resonators terminated by resistors. By heating one of the resistors and monitoring the temperatures of the other two, we determine photonic heat currents in the system and demonstrate their tunability by magnetic field at the level of 1 aW. We determine system parameters by performing microwave transmission measurements on a separate nominally identical sample and, in this way, demonstrate clear correlation between the level splitting of the qubit and the heat currents flowing through it. Our experiment is an important step towards realization of heat transistors, heat amplifiers, masers pumped by heat and other quantum heat transport devices.