Zero-frequency noise in adiabatically driven, interacting quantum systems

We investigate current-current correlations of adiabatic charge pumping through interacting quantum dots weakly coupled to reservoirs. To calculate the zero-frequency noise for a time-dependently driven system, possibly in the presence of an additional dc bias, we perform within a real-time diagrammatic approach a perturbative expansion in the tunnel coupling to the reservoirs in leading and next-to-leading order. We apply this formalism to study the adiabatic correction to the zero-frequency noise, i.e., the pumping noise, in the case of a single-level quantum dot charge pump. If no stationary bias is applied, the adiabatic correction shows Coulomb-interaction-induced deviations from the fluctuation-dissipation theorem. Furthermore, we show that the adiabatic correction to the Fano factor carries information about the coupling asymmetry and is independent of the choice of the pumping parameters. When including a time-dependent finite bias, we find that there can be pumping noise even if there is zero adiabatically pumped charge. The pumping noise also indicates the respective direction of the bias-induced current and the pumping current

Psychopathology of perversion: a contemporary reflexion of violence

Cet article s’inscrit dans un double projet qui consiste d’une part à interroger la psychopathologie de la perversion à partir de l’évaluation des rapports complexes entre violence et psychopathologie, et d’autre part de mettre au travail les repères métapsychologiques à partir desquels peut être pensé ce mode d’organisation/d’aménagement psychique de la personnalité. L’objectif, in fine, est d’apporter une contribution à la compréhension des dynamiques psychiques engagées dans ce que l’on nomme la perversion, au service de la mise en œuvre et du déploiement du travail psychothérapeutique. Dans un premier temps, l’auteur propose une double mise au point concernant les rapports complexes entre agir et psychopathologie, et la manière dont la pratique de l’expertise psychologique judiciaire rencontre la question de la perversion, tout à la fois d’un point de vue clinique et d’un point de vue politique. Dans un second temps, l’auteur développera un certain nombre de points de vue théoriques qui permettent d’affiner une compréhension psychodynamique des différentes configurations de la psychopathologie de la perversion, en la situant, d’un point de vue structurel, entre état-limite et psychose. Dans un troisième temps, la clinique de la perversion se trouvera mise à l’épreuve, à partir d’une pratique médico-légale, dans le double champ de la clinique adulte et de la clinique adolescente

Readout of relaxation rates by nonadiabatic pumping spectroscopy

We put forward nonadiabatic charge pumping as a method for accessing the different charge relaxation rates as well as the relaxation rates of excited orbital states in double-quantum-dot setups, based on extremely size-limited quantum dots and dopant systems. The rates are obtained in a well-separated manner from plateaus, occurring when comparing the steady-state current for reversed driving cycles. This yields a reliable readout independent of any fitting parameters. Importantly, the nonadiabatic pumping spectroscopy essentially exploits the same driving scheme as the operation of these devices generally employs. We provide a detailed analysis of the working principle of the readout scheme as well as of possible errors, thereby demonstrating its broad applicability. The precise knowledge of relaxation rates is highly relevant for the implementation of time-dependently operated devices, such as electron pumps for metrology or qubits in quantum information.Comment: 14 pages, 5 figure

Fractional charges in conventional sequential electron tunneling

The notion of fractional charges was up until now reserved for quasiparticle excitations emerging in strongly correlated quantum systems, such as Laughlin states in the fractional quantum Hall effect, Luttinger quasiparticles, or parafermions. Here, we consider topological transitions in the full counting statistics of standard sequential electron tunneling, and find that they lead to the same type of charge fractionalization - strikingly without requiring exotic quantum correlations. This conclusion relies on the realization that fundamental integer charge quantization fixes the global properties of the transport statistics whereas fractional charges can only be well-defined locally. We then show that the reconciliation of these two contradicting notions results in a nontrivially quantized geometric phase defined in the detector space. In doing so, we show that detector degrees of freedom can be used to describe topological transitions in nonequilibrium open quantum systems. Moreover, the quantized geometric phase reveals a profound analogy between the fractional charge effect in sequential tunneling and fractional Josephson effect in topological superconducting junctions, where likewise the Majorana- or parafermions exhibit a charge which is at odds with the Cooper pair charge as the underlying unit of the supercurrent. In order to provide means for an experimental verification of our claims, we demonstrate the fractional nature of transport statistics at the example of highly feasible transport models, such as weakly tunnel-coupled quantum dots or charge islands. We then show that the geometric phase can be accessed through the detector's waiting time distribution. Finally, we find that topological transitions in the transport statistics could even lead to new applications, such as the unexpected possibility to directly measure features beyond the resolution limit of a detector.Comment: 28 pages, 10 figures; Supplemental Material linked under ancillary file

Charge quantization and detector resolution

Charge quantization, or the absence thereof, is a central theme in quantum circuit theory, with dramatic consequences for the predicted circuit dynamics. Very recently, the question of whether or not charge should actually be described as quantized has enjoyed renewed widespread interest, with however seemingly contradictory propositions. Here, we intend to reconcile these different approaches, by arguing that ultimately, charge quantization is not an intrinsic system property, but instead depends on the spatial resolution of the charge detector. We show that the latter can be directly probed by unique geometric signatures in the correlations of the supercurrent. We illustrate these findings at the example Josephson junction arrays in the superinductor regime, where the transported charge appears to be continuous. Finally, we comment on potential consequences of charge quantization beyond superconducting circuits.Comment: 26 pages, 3 figure

Control of Andreev bound state population and related charge-imbalance effect

Motivated by recent experimental research, we study the processes in an ac driven superconducting constriction whereby one quasiparticle is promoted to the delocalized states outside the superconducting gap. We demonstrate that with these processes one can control the population of the Andreev bound states in the constriction. We stress an interesting charge asymmetry of these processes that may produce a charge imbalance of accumulated quasiparticles, which depends on the phase

Compact description of quantum phase slip junctions

Quantum circuit theory is a powerful and ever-evolving tool to predict the dynamics of superconducting circuits. In its language, quantum phase slips (QPSs) are famously considered to be the exact dual to the Josephson effect. However, this duality renders the integration of QPS junctions into a unified theoretical framework very difficult, and as we show, gives rise to serious inconsistencies for different formalisms, and in some cases difficulties to include time-dependent flux driving. We propose to resolve these issues by reducing and compactifying the Hilbert space describing the QPS processes. Our treatment provides for the first time a unified description of the Aharonov-Bohm and Aharonov-Casher effects, properly defines the valid form of inductive interactions to an environment, and allows to account for recent insights on how to include electromotive forces. Finally, we show that the compactification is likewise important for correctly predicting the available computational space for qubit architectures involving QPS junctions.Comment: 25 pages, 7 figures, supplementary. Revisions in main text and supplementar

Transport fluctuation relations in interacting quantum pumps

The understanding of out-of-equilibrium fluctuation relations in small open quantum systems has been a focal point of research in recent years. In particular, for systems with adiabatic time-dependent driving, it was shown that the fluctuation relations known from stationary systems do no longer apply due the geometric nature of the pumping current response. However, the precise physical interpretation of the corrected pumping fluctuation relations as well as the role of many-body interactions remained unexplored. Here, we study quantum systems with many-body interactions subject to slow time-dependent driving, and show that fluctuation relations of the charge current can in general not be formulated without taking into account the total energy current put into the system through the pumping process. Moreover, we show that this correction due to the input energy is nonzero only when Coulomb-interactions are present. Thus, fluctuation response relations offer an until now unrevealed opportunity to probe many-body correlations in quantum systems. We demonstrate our general findings at the concrete example of a single-level quantum dot model, and propose a scheme to measure the interaction-induced discrepancies from the stationary case.Comment: 13 pages, 2 figure