Archive ouverte UNIGE | last documents for author 'Patrick Hofer'https://archive-ouverte.unige.ch/Latest objects deposited in the Archive ouverte UNIGE for author 'Patrick Hofer'engOptimal work extraction from quantum states by photo-assisted Cooper pair tunnelinghttps://archive-ouverte.unige.ch/unige:127274https://archive-ouverte.unige.ch/unige:127274The theory of quantum thermodynamics predicts fundamental bounds on work extraction from quantum states. As these bounds are derived in a very general and abstract setting, it is unclear how relevant they are in an experimental context, where control is typically limited. Here we address this question by showing that optimal work extraction is possible for a realistic engine. The latter consists of a superconducting circuit, where a LC-resonator is coupled to a Josephson junction. The oscillator state fuels the engine, providing energy absorbed by Cooper pairs, thus producing work in the form of an electrical current against an external voltage bias. We show that this machine can extract the maximal amount of work from all Gaussian and Fock states. Furthermore, we consider work extraction from a continuously stabilized oscillator state. In both scenarios, coherence between energy eigenstates is beneficial, increasing the power output of the machine. This is possible because the phase difference across the Josephson junction provides a phase reference.Tue, 03 Dec 2019 14:11:33 +0100Dynamic mesoscopic conductors: single electron sources, full counting statistics, and thermal machineshttps://archive-ouverte.unige.ch/unige:88977https://archive-ouverte.unige.ch/unige:88977We theoretically investigate questions regarding the controlled emission and entanglement of individual electrons in mesoscopic circuits, the statistics of current fluctuations and electron waiting times for phase-coherent quantum transport, and thermal machines such as heat engines and refrigerators at the nano-scale. Chapter 2 focuses on dynamic single-electron sources, specifically on the generation of ac spin currents in topological insulators, Mach-Zehnder interferometry with periodic voltage pulses, and the on-demand entanglement of few-electron excitations. In Chapter 3, we present a novel theory for joint electron waiting times and we connect the occurence of negative values in the full counting statistics to a peculiar interference effect. Chapter 4 discusses a heat engine based on the interference in a Mach-Zehnder interferometer as well as implementations for the arguably smallest thermal machines making use of a Josephson junction coupled to harmonic oscillators.Wed, 16 Nov 2016 11:07:47 +0100Single-electron entanglement and nonlocalityhttps://archive-ouverte.unige.ch/unige:84466https://archive-ouverte.unige.ch/unige:84466Motivated by recent progress in electron quantum optics, we revisit the question of single-electron entanglement, specifically whether the state of a single electron in a superposition of two separate spatial modes should be considered entangled. We first discuss a gedanken experiment with single-electron sources and detectors, and demonstrate deterministic (i. e. without post-selection) Bell inequality violation. This implies that the single-electron state is indeed entangled and, furthermore, nonlocal. We then present an experimental scheme where single-electron entanglement can be observed via measurements of the average currents and zero-frequency current cross-correlators in an electronic Hanbury Brown-Twiss interferometer driven by Lorentzian voltage pulses. We show that single-electron entanglement is detectable under realistic operating conditions. Our work settles the question of single-electron entanglement and opens promising perspectives for future experiments.Mon, 13 Jun 2016 11:16:07 +0200