### Browsing by Author "Potanina, Elina"

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Item Electron waiting times of a periodically driven single-electron turnstile(2017-07-17) Potanina, Elina; Flindt, Christian; Department of Applied PhysicsWe investigate the distribution of waiting times between electrons emitted from a periodically driven single-electron turnstile. To this end, we develop a scheme for analytic calculations of the waiting time distributions for arbitrary periodic driving protocols. We illustrate the general framework by considering a driven tunnel junction before moving on to the more involved single-electron turnstile. The waiting time distributions are evaluated at low temperatures for square-wave and harmonic driving protocols. In the adiabatic regime, the dynamics of the turnstile is synchronized with the external drive. As the nonadiabatic regime is approached, the waiting time distribution becomes dominated by cycle-missing events in which the turnstile fails to emit within one or several periods. We also discuss the influence of finite electronic temperatures. The waiting time distributions provide a useful characterization of the driven single-electron turnstile with complementary information compared to what can be learned from conventional current measurements.Item Optimization of quantized charge pumping using full counting statistics(American Physical Society, 2019-01-24) Potanina, Elina; Brandner, Kay; Flindt, Christian; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum TransportWe optimize the operation of single-electron charge pumps using full counting statistics techniques. To this end, we evaluate the statistics of pumped charge on a wide range of driving frequencies using Floquet theory, focusing here on the current and the noise. For charge pumps controlled by one or two gate voltages, we demonstrate that our theoretical framework may lead to enhanced device performance. Specifically, by optimizing the driving parameters, we predict a significant increase in the frequencies for which a quantized current can be produced. For adiabatic two-parameter pumps, we exploit that the pumped charge and the noise can be expressed as surface integrals over Berry curvatures in parameter space. Our findings are important for the efforts to realize high-frequency charge pumping, and our predictions may be verified using current technology.Item Optimization of Quantum Pumps(Aalto University, 2019) Potanina, Elina; Teknillisen fysiikan laitos; Department of Applied Physics; Quantum Transport Group; Perustieteiden korkeakoulu; School of Science; Flindt, Christian, Prof., Aalto University, Department of Applied Physics, FinlandThe SI unit system has recently moved away from artificial definitions of units to the elegant quantum definitions based on natural constants. The previous definition of the ampere involved the force between two infinitely long wires, and it is now replaced by the quantum ampere, where current is defined using the elementary charge and caesium frequency standard. Recent developments in quantum technology and nano-device fabrication have already enabled on-demand single-electron delivery. Experimental realization of the quantum ampere with close-to-metrological accuracy was recently demonstrated using single-electron pumps based on quantum dots with tunable-barriers. In this thesis, I develop optimization schemes tailored for the experimentally available devices such as single-electron turnstiles and tunable-barrier quantum pumps. I employ theories of quantum transport for periodically driven systems in the low- and high-frequency regimes, to answer the following questions: What is the optimal operation cycle for a quantum pump to achieve high accuracy in the GHz regime? How can we increase the breakdown frequency of single-electron pumps? I optimize the regularity of emitted electrons in a turnstile using the distribution of electron waiting-times. I provide an analytic optimization of two-parameter charge pumps based on the symmetries of the corresponding Berry curvature. For one-parameter pumps, I evaluate the breakdown frequency via a high-frequency expansion and optimize it so that it increases by one order of magnitude. Within the framework of non-equilibrium quantum thermodynamics, I demonstrate how it is possible to maximize the coefficient of performance for coherent pumps.Item Thermodynamic bounds on coherent transport in periodically driven conductors(American Physical Society, 2021-04-14) Potanina, Elina; Flindt, Christian; Moskalets, Michael; Brandner, Kay; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Transport; National Technical University Kharkov Polytechnical Institute; Keio UniversityPeriodically driven coherent conductors provide a universal platform for the development of quantum transport devices. Here, we lay down a comprehensive theory to describe the thermodynamics of these systems. We first focus on moderate thermoelectrical biases and low driving frequencies. For this linear response regime, we establish generalized Onsager-Casimir relations and an extended fluctuation-dissipation theorem. Furthermore, we derive a family of thermodynamic bounds proving that any local matter or heat current puts a nontrivial lower limit on the overall dissipation rate of a coherent transport process. These bounds do not depend on system-specific parameters, are robust against dephasing, and involve only experimentally accessible quantities. They thus provide powerful tools to optimize the performance of mesoscopic devices and for thermodynamic inference, as we demonstrate by working out three specific applications. We then show that physically transparent extensions of our bounds hold also for strong biases and high frequencies. These generalized bounds imply a thermodynamic uncertainty relation that fully accounts for quantum effects and periodic driving. Moreover, they lead to a universal and operationally accessible bound on entropy production that can be readily used for thermodynamic inference and device engineering far from equilibrium. Connecting a broad variety of topics that range from thermodynamic geometry over thermodynamic uncertainty relations to quantum engineering, our work provides a unifying thermodynamic theory of coherent transport that can be tested and utilized with current technologies.Item Waiting time distributions in a two-level fluctuator coupled to a superconducting charge detector(American Physical Society, 2019-12-10) Jenei, Mate; Potanina, Elina; Zhao, Ruichen; Tan, Kuan Y.; Rossi, Alessandro; Tanttu, Tuomo; Chan, Kok W.; Sevriuk, Vasilii; Mottonen, Mikko; Dzurak, Andrew; Centre of Excellence in Quantum Technology, QTF; University of New South Wales; Department of Applied Physics; National Physical Laboratory (NPL)We analyze charge fluctuations in a parasitic state strongly coupled to a superconducting Josephson-junction-based charge detector. The charge dynamics of the state resembles that of electron transport in a quantum dot with two charge states, and hence we refer to it as a two-level fluctuator. By constructing the distribution of waiting times from the measured detector signal and comparing it with a waiting time theory, we extract the electron in- and out-tunneling rates for the two-level fluctuator, which are severely asymmetric.