arXiv subjects

Janine Splettstoesser

Publications and source records attributed to Janine Splettstoesser.

At least 55 records · Page 3Linked to original sources

arXiv2022

Influence of channel mixing in fermionic Hong-Ou-Mandel experiments

We consider an electronic Hong-Ou-Mandel interferometer in the integer quantum Hall regime, where the colliding electronic states are generated by applying voltage pulses (creating for instance Levitons) to ohmic contacts. The aim of this work is to investigate possible mechanisms leading to a reduced visibility of the Pauli dip, i.e., the noise suppression expected for synchronized sources. It is known that electron-electron interactions cannot account for this effect and always lead to a full suppression of the Hong-Ou-Mandel noise. Focusing on the case of filling factor $ν=2$, we show instead that a reduced visibility of the Pauli dip can result from mixing of the copropagating edge channels, arising from tunneling events between them.

cond-mat.mes-hall↗

arXiv2021

Readout of quantum screening effects using a time-dependent probe

In voltage- and temperature-biased coherent conductors quantum screening effects occur if the conductor's transmission is energy-dependent. Here, we show that an additional ac-driven terminal can act as a probe for a direct readout of such effects, hitherto unexplored. We find that screening of charges induced by the static biases impacts already their standard linear thermoelectric response coefficients due to nonlinear effects when accounting for the frequency of the time-dependent driving. Those effects should be observable under realistic experimental conditions and can literally be switched on and off with the ac-driving.

cond-mat.mes-hall↗

arXiv2021

General bounds on electronic shot noise in the absence of currents

We investigate the charge and heat electronic noise in a generic two-terminal mesoscopic conductor in the absence of the corresponding charge and heat currents. Despite these currents being zero, shot noise is generated in the system. We show that, irrespective of the conductor's details and the specific nonequilibrium conditions, the charge shot noise never exceeds its thermal counterpart, thus establishing a general bound. Such a bound does not exist in the case of heat noise, which reveals a fundamental difference between charge and heat transport under zero-current conditions.

cond-mat.mes-hall↗

arXiv2021

Optomechanical cooling with coherent and squeezed light: the thermodynamic cost of opening the heat valve

Ground-state cooling of mechanical motion by coupling to a driven optical cavity has been demonstrated in various optomechanical systems. In our work, we provide a so far missing thermodynamic performance analysis of optomechanical sideband cooling in terms of a heat valve. As performance quantifiers, we examine not only the lowest reachable effective temperature (phonon number) but also the evacuated-heat flow as an equivalent to the cooling power of a standard refrigerator, as well as appropriate thermodynamic efficiencies, which all can be experimentally inferred from measurements of the cavity output light field. Importantly, in addition to the standard optomechanical setup fed by coherent light, we investigate two recent alternative setups for achieving ground-state cooling: replacing the coherent laser drive by squeezed light or using a cavity with a frequency-dependent (Fano) mirror. We study the dynamics of these setups within and beyond the weak-coupling limit and give concrete examples based on parameters of existing experimental systems. By applying our thermodynamic framework, we gain detailed insights into these three different optomechanical cooling setups, allowing a comprehensive understanding of the thermodynamic mechanisms at play.

quant-ph↗

arXiv2021

Stochastic Thermodynamic Cycles of a Mesoscopic Thermoelectric Engine

We analyze a steady-state thermoelectric engine, whose working substance consists of two capacitively coupled quantum dots. One dot is tunnel-coupled to a hot reservoir serving as a heat source, the other one to two electrically biased reservoirs at a colder temperature, such that work is extracted under the form of a steady-state current against the bias. In single realizations of the dynamics of this steady-state engine autonomous, 4-stroke cycles can be identified. The cycles are purely stochastic, in contrast to mechanical autonomous engines which exhibit self-oscillations. In particular, these cycles fluctuate in direction and duration, and occur in competition with other spurious cycles. Using a stochastic thermodynamic approach, we quantify the cycle fluctuations and relate them to the entropy produced during individual cycles. We identify the cycle mainly responsible for the engine performance and quantify its statistics with tools from graph theory. We show that such stochastic cycles are made possible because the work extraction mechanism is itself stochastic instead of the periodic time dependence in the working-substance Hamiltonian which can be found in conventional mechanical engines. Our investigation brings new perspectives about the connection between cyclic and steady-state engines.

quant-ph↗

arXiv2020

Phase-coherent heat circulators with normal- or superconducting contacts

We investigate heat circulators where a phase coherent region is contacted by three leads that are either normal- or superconducting. A magnetic field, and potentially the superconducting phases, allow to control the preferential direction of the heat flow between the three-different temperature-biased contacts. The main goal of this study is to analyze the requirements for heat circulation in non-ideal devices, in particular focusing on sample-to-sample variations. Quite generally, we find that the circulation performance of the devices is good as long as only a few transport channels are involved. We compare the performance of circulators with normalconducting contacts to those with superconducting contacts and find that the circulation coefficient are essentially unchanged.

cond-mat.mes-hall↗

arXiv2020

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.

cond-mat.mes-hall↗

arXiv2020

Quantifying nonequlibrium thermodynamic operations in a multiterminal mesoscopic system

We investigate a multiterminal mesoscopic conductor in the quantum Hall regime, subject to temperature and voltage biases. The device can be considered as a nonequilibrium resource acting on a working substance. We previously showed that cooling and power production can occur in the absence of energy and particle currents from a nonequilibrium resource (calling this an N-demon). Here we allow energy or particle currents from the nonequilibrium resource and find that the device seemingly operates at a better efficiency than a Carnot engine. To overcome this problem, we define free-energy efficiencies which incorporate the fact that a nonequilibrium resource is consumed in addition to heat or power. These efficiencies are well behaved for equilibrium and nonequilibrium resources and have an upper bound imposed by the laws of thermodynamics. We optimize power production and cooling in experimentally relevant parameter regimes.

cond-mat.mes-hall↗

arXiv2020

Detailed study of nonlinear cooling with two-terminal configurations of topological edge states

We study the nonlinear thermoelectric cooling performance of a quantum spin Hall system. The setup consists of a nanomagnet contacting a Kramers' pair of helical edge states, resulting in a transmission probability with a rich structure containing peaks, well-type, and step-type features. We present a detailed analysis of the impact of all these features on the cooling performance, based to a large extent on analytical results. We analyze the cooling power as well as the coefficient of performance of the device. Since the basic features we study may be present in the transmission function of other mesoscopic conductors, our conclusions provide useful insights to analyze the nonlinear thermoelectric behavior of a wide class of quantum devices. The combination of all these properties define the response of the quantum spin Hall setup, for which we provide some realistic estimates for the conditions limiting and optimizing its operation as a cooling device.

cond-mat.mes-hall↗

arXiv2020

Thermovoltage in quantum dots with attractive interaction

We study the linear and nonlinear thermovoltage of a quantum dot with effective attractive electron-electron interaction and weak, energy-dependent tunnel-coupling to electronic contacts. Remarkably, we find that the thermovoltage shows signatures of repulsive interaction which can be rationalized. These thermovoltage characteristics are robust against large potential and temperature differences well into the nonlinear regime, which we expect can be demonstrated in current state-of-the-art experiments. Furthermore, under nonlinear operation, we find extended regions of large power production at efficiencies on the order of the Curzon-Ahlborn bound interrupted only by a characteristic sharp dip.

cond-mat.mes-hall↗

arXiv2019

Non-equilibrium System as a Demon

Maxwell demons are creatures that are imagined to be able to reduce the entropy of a system without performing any work on it. Conventionally, such a Maxwell demon's intricate action consists of measuring individual particles and subsequently performing feedback. Here we show that much simpler setups can still act as demons: we demonstrate that it is sufficient to exploit a non-equilibrium distribution to seemingly break the second law of thermodynamics. We propose both an electronic and an optical implementation of this phenomenon, realizable with current technology.

cond-mat.mes-hall↗

arXiv2019

Mesoscopic effects in the heat conductance of superconducting-normal-superconducting and normal-superconducting junctions

We study the heat conductance of hybrid superconducting junctions. Our analysis involves single-channel junctions with arbitrary transmission as well as diffusive connectors and shows the influence of the superconducting gaps and phases of the contacts on the heat conductance. If the junction is diffusive, these effects are completely quenched on average, however, we find that their influence persists in weak-localization corrections and conductance fluctuations. While these statistical properties strongly deviate from the well-known analogues for the charge conductance, we demonstrate that the heat conductance fluctuations maintain a close to universal behavior. We find a generalized Wiedemann-Franz law for Josephson junctions with equal gaps and vanishing phase difference.

cond-mat.mes-hall↗

arXiv2019

Power, Efficiency and Fluctuations in a Quantum Point Contact as Steady-State Thermoelectric Heat Engine

The trade-off between large power output, high efficiency and small fluctuations in the operation of heat engines has recently received interest in the context of thermodynamic uncertainty relations (TURs). Here we provide a concrete illustration of this trade-off by theoretically investigating the operation of a quantum point contact (QPC) with an energy-dependent transmission function as a steady-state thermoelectric heat engine. As a starting point, we review and extend previous analysis of the power production and efficiency. Thereafter the power fluctuations and the bound jointly imposed on the power, efficiency and fluctuations by the TURs are analyzed as additional performance quantifiers. We allow for arbitrary smoothness of the transmission probability of the QPC, which exhibits a close to step-like dependence in energy, and consider both the linear and the non-linear regime of operation. It is found that for a broad range of parameters, the power production reaches nearly its theoretical maximum value, with efficiencies more than half of the Carnot efficiency and at the same time with rather small fluctuations. Moreover, we show that by demanding a non-zero power production, in the linear regime a stronger TUR can be formulated in terms of the thermoelectric figure of merit. Interestingly, this bound holds also in a wide parameter regime beyond linear response for our QPC device.

cond-mat.mes-hall↗

arXiv2019

Thermal transistor and thermometer based on Coulomb-coupled conductors

We study a three-terminal setup consisting of a single-level quantum dot capacitively coupled to a quantum point contact. The point contact connects to a source and drain reservoirs while the quantum dot is coupled to a single base reservoir. This setup has been used to implement a noninvasive, nanoscale thermometer for the bath reservoir by detecting the current in the quantum point contact. Here, we demonstrate that the device can also be operated as a thermal transistor where the average (charge and heat) current through the quantum point contact is controlled via the temperature of the base reservoir. We characterize the performances of this device both as a transistor and a thermometer, and derive the operating condition maximizing their respective sensitivities. The present analysis is useful for the control of charge and heat flow and high precision thermometry at the nanoscale.

cond-mat.mes-hall↗

arXiv2019

Minimal-excitation single-particle emitters: A comparison of charge and energy transport properties

We investigate different types of time-dependently driven single-particle sources whose common feature is that they produce pulses of integer charge and minimally excite the Fermi sea. These sources are: a slowly driven mesoscopic capacitor, a Lorentzian-shaped time-dependent bias voltage, and a local gate-voltage modulation of a quantum Hall edge state. They differ by their specific driving protocols, e.g., they have a pure ac driving or a driving with a dc component. In addition, only in the first of these setups, strong confinement leading to a discrete energy spectrum of the conductor, is exploited for the single-particle emission. Here, we study if and how these basic differences impact transport properties. Specifically, we address time- and energy-resolved charge and energy currents, as well as their zero-frequency correlators (charge-, energy- and mixed noise), as they are frequently used to characterize experiments in quantum optics with electrons. Beyond disparities due to a different number and polarity of particles emitted per period, we in particular identify differences in the impact, which temperature has on the observables for sources with and without energy-dependent scattering properties. We trace back these characteristics to a small set of relevant parameter ratios.

cond-mat.mes-hall↗

arXiv2018

Quantum thermodynamics of nanoscale thermoelectrics and electronic devices

This mini-review is intended as a short introduction to electron flow in nanostructures. Its aim is to provide a brief overview of this topic for people who are interested in the thermodynamics of quantum systems but know little about nanostructures. We particularly emphasize devices that work in the steady-state, such as simple thermoelectrics, but also mention cyclically driven heat engines. We do not aim to be either complete or rigorous, but use a few pages to outline some of the main ideas in the topic.

cond-mat.mes-hall↗

arXiv2018

Vibration-induced modulation of magnetic anisotropy in a magnetic molecule

We theoretically analyze the spectrum of a magnetic molecule when its charge and spin can couple to the molecular vibrations. More specifically, we show that the interplay between charge-vibron and spin-vibron coupling leads to a renormalization of the magnetic anisotropy parameters of the molecule. This effect is discussed for a model device consisting of an individual magnetic molecule embedded in a junction. We study the transport properties of the device and illustrate how the differential conductance is affected by the vibrationally induced renormalization of the magnetic anisotropy. Depending on the total molecular spin and the bare (intrinsic) magnetic anisotropy, the induced modulation can lead to visible shifts and crossings in the spectrum, and it can even be the cause of a transport blockade. It is therefore of particular interest to use mechanically controllable break junctions, since in such a case, the relevant coupling between the molecular spin and vibrations can be controlled via deformations of the molecule when stretching or compressing the junction.

cond-mat.mes-hall↗

arXiv2018

Finite-frequency noise of interacting single-electron emitters: spectroscopy with higher noise harmonics

We derive the symmetrized current-noise spectrum of a quantum dot, which is weakly tunnel-coupled to an electron reservoir and driven by a slow time-dependent gate voltage. This setup can be operated as an on-demand emitter of single electrons into a mesoscopic conductor. By extending a real-time diagrammatic technique which is perturbative in the tunnel coupling, we obtain the time-resolved finite-frequency noise as well as its decomposition into noise harmonics in the presence of both strong Coulomb interaction and slow time-dependent driving. We investigate the noise over a large range of frequencies and point out where the interplay of Coulomb interaction and driving leads to unique signatures in finite-frequency noise spectra, in particular in the first harmonic. Besides that, we employ the first noise harmonic as a spectroscopic tool to access individual fluctuation processes. We discuss how the inverse noise frequency sets a time scale for fluctuations, which competes with time scales of the quantum-dot relaxation dynamics as well as the driving.

cond-mat.mes-hall↗