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The 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.
|Translated title of the contribution||Optimization of Quantum Pumps|
|Publication status||Published - 2019|
|MoE publication type||G5 Doctoral dissertation (article)|
- quantum pumps
- adiabatic pumping
- single-electron pumps
- counting statistics
- distribution of waiting times
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