arXiv subjects

Michael Moskalets

Publications and source records attributed to Michael Moskalets.

At least 37 records · Page 2Linked to original sources

arXiv2016

Dynamics of energy transport and entropy production in ac-driven quantum electron systems

We analyze the time-resolved energy transport and the entropy production in ac-driven quantum coherent electron systems coupled to multiple reservoirs at finite temperature. At slow driving we formulate the first and second laws of thermodynamics valid at each instant of time. We identify heat fluxes flowing though the different pieces of the device and emphasize the importance of the energy stored in the contact and central regions for the second law of thermodynamics to be instantaneously satisfied. In addition, we discuss conservative and dissipative contributions to the heat flux and to the entropy production as a function of time. We illustrate these ideas with a simple model corresponding to a driven level coupled to two reservoirs with different chemical potentials.

cond-mat.mes-hall↗

arXiv2016

Half-levitons -- zero-energy excitations of a driven Fermi sea

A voltage pulse of a Lorentzian shape carrying a half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasi-particle with an effectively fractional charge $e/2$. A prominent feature of such an excitation is a narrow peak in the energy distribution function laying exactly at the Fermi energy $ μ$. Another spectacular feature is that the distribution function has symmetric tails as above as below $ μ$, which results in a zero energy of an excitation. This sounds improbable since at zero temperature all available states below $ μ$ are fully occupied. The resolution is lying in the fact that such a voltage pulse excites also electron-hole pairs which free some space below $ μ$ and thus allow a zero-energy quasi-particle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in experiment.

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arXiv2015

Single-electron coherence: finite temperature versus pure dephasing

We analyze a coherent injection of single electrons on top of the Fermi sea in two situations, at finite-temperature and in presence of pure dephasing. Both finite-temperature and pure dephasing change the property of the injected quantum states from pure to mixed. However, we show that the temperature-induced mixedness does not alter the coherence properties of these single-electronic states. In particular two such mixed states exhibit perfect antibunching while colliding at an electronic wave splitter. This is in striking difference with the dephasing-induced mixedness which suppresses antibunching. On the contrary, a single-particle shot noise is suppressed at finite temperatures but is not affected by pure dephasing. This work therefore extends the investigation of the coherence properties of single-electronic states to the case of mixed states and clarifies the difference between different types of mixedness.

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arXiv2015

Interference and multi-particle effects in a Mach-Zehnder interferometer with single-particle sources

We investigate a Mach-Zehnder interferometer fed by two time-dependently driven single-particle sources, one of them placed in front of the interferometer, the other in the center of one of the arms. As long as the two sources are operated independently, the signal at the output of the interferometer shows an interference pattern, which we analyze in the spectral current, in the charge and energy currents, as well as in the charge current noise. The synchronization of the two sources in this specifically designed setup allows for collisions and absorptions of particles at different points of the interferometer, which have a strong impact on the detected signals. It introduces further relevant time-scales and can even lead to a full suppression of the interference in some of the discussed quantities. The complementary interpretations of this phenomenon in terms of spectral properties and tunable two-particle effects (absorptions and quantum exchange effects) are put forward in this article.

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arXiv2015

First-order correlation function of the stream of single-electron wave-packets

The first-order correlation function, which is accessible experimentally, contains all essential information about the state of the system of non-interacting electrons. Here I discuss how this function can be used to answer the question whether the state of a periodic stream of single-electron wave-packets is a multi-particle state or it is the product of single-particle states. In the latter case the correlation function is expected to be factorizable while in the former case it is not. As an example I consider a train of Lorentzian in shape single-electron excitations, levitons. I demonstrate that the correlation function in time domain is factorizable or not depending on whether the wave-packets are separated or overlapping. In contrast, the correlation function in energy domain is always factorizable and thus cannot be used to distinguish single- and multi-particle states.

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arXiv2014

Floquet scattering matrix theory of heat fluctuations in dynamical quantum conductors

I present the Floquet scattering matrix theory of low-frequency heat fluctuations in driven multi-terminal quantum-coherent conductors in the linear response regime and beyond. The intrinsic fluctuations of energy of dynamically excited electrons are identified as the fundamental source of a heat noise not revealed by the electrical noise. The role of backscattering in the increase of a heat noise above the level defined by the Callen-Welton fluctuation-dissipation theorem, is highlighted.

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arXiv2014

Long-range Fermi sea correlations as the resource for encoding quantum information

An extra constant phase can be added to the wave function of a finite-length portion of a chiral Fermi sea. This phase can be read-out with the help of an imbalanced interferometer, where such a phase carrier interferes with the reference Fermi sea. As a result of such interference, the same in value but opposite in sign charge is appeared at interferometer's outputs. A phase carrier consists of electron-hole pairs residing on the surface of the Fermi sea. Importantly, these pairs are not only electrically neutral, but in addition do not carry heat. A phase carrier can be created, for instance, with the help of an on-demand single-electron source able to produce excitations with a multiple-peak density profile.

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arXiv2013

Dynamical energy transfer in ac driven quantum systems

We analyze the time-dependent energy and heat flows in a resonant level coupled to a fermionic continuum. The level is periodically forced with an external power source that supplies energy into the system. Based on the tunneling Hamiltonian approach and scattering theory, we discuss the different contributions to the total energy flux. We then derive the appropriate expression for the dynamical dissipation, in accordance with the fundamental principles of thermodynamics. Remarkably, we find that the dissipated heat can be expressed as a Joule law with a universal resistance that is constant at all times.

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arXiv2013

Two-electron state from the Floquet scattering matrix perspective

Two single-particle sources coupled in series to a chiral electronic waveguide can serve as a probabilistic source of two-particle excitations with tunable properties. The second-order correlation function, characterizing the state of emitted electrons in space-time, is expressed in terms of the Floquet scattering matrix of a source. It is shown that the Fourier transform of the correlation function, characterizing the emitted state in energy space, can be accessed with the help of an energy resolved shot-noise measurement. The two-electron state emitted adiabatically is discussed in detail. In particular, the two-electron wave function is represented via two different sets of single-particle wave functions accessible experimentally.

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arXiv2013

Transport phenomena in helical edge states interferometers. A Green's function approach

We analyze the current and the shot-noise of an electron interferometer made of the helical edge states of a two-dimensional topological insulator within the framework of non-equilibrium Green's functions formalism. We study in detail setups with a single and with two quantum point contacts inducing scattering between the different edge states. We consider processes preserving the spin as well as the effect of spin-flip scattering. In the case of a single quantum point contact, a simple test based on the shot-noise measurement is proposed to quantify the strength of the spin-flip scattering. In the case of two single point contacts with the additional ingredient of gate voltages applied within a finite-size region at the top and bottom edges of the sample, we identify two type of interference processes in the behavior of the currents and the noise. One of such processes is analogous to that taking place in a Fabry-Pérot interferometer, while the second one corresponds to a configuration similar to a Mach-Zehnder interferometer. In the helical interferometer these two processes compete.

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arXiv2013

Thermoelectric performance of a driven double quantum dot

In this paper we investigate the thermoelectric performance of a double-dot device driven by time-dependently modulated gate voltages. We show that if the modulation frequency Ω is sufficiently small, not only quantized charge pumping can be realized, but also the heat current flowing in the leads is quantized and exhibits plateaux in units of kB T ln2 Ω/2π. The factor ln2 stems from the degeneracy of the double-dot states involved into transport. This opens the possibility of using the pumping cycle to transfer heat against a temperature gradient or to extract work from a hot reservoir with Carnot efficiency. However, the performance of a realistic device is limited by dissipative effects due to leakage currents and finite-frequency operation, which we take into account rigorously by means of a generalized master equation approach in the regime where the double dot is weakly coupled to the leads. We show that despite these effects, the efficiency of a double-dot charge pump performing work against a dc-source can reach of up to 70% of the ideal value.

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arXiv2013

Noise of a single-electron emitter

I analyze the correlation function of currents generated by the periodically driven quantum capacitor emitting single electrons and holes into the chiral waveguide. I compare adiabatic and non-adiabatic, transient working regimes of a single-electron emitter and find the striking difference between the correlation functions in two regimes. Quite generally for the system driven with frequency $Ω$ the correlation function depends on two frequencies, $ω$ and $\ell Ω- ω$, where $\ell$ is an integer. For the emitter driven non-adiabatically the correlation functions for different $\ell$ are similar and almost symmetric in $ω$. While in the case of adiabatic drive the correlation functions for $\ell \ne 0$ are highly asymmetric in $ω$ and exceed significantly the one corresponding to $\ell = 0$. Under optimal operating conditions the correlation function for odd $\ell$ is zero.

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arXiv2013

Floquet scattering matrix approach to the phase noise of a single-electron source in the adiabatic regime

We give the basic elements of the Floquet scattering matrix approach to the dynamic quantum transport in mesoscopic and nanoscopic conductors. We use the scattering formalism to discuss the noise power spectrum of a single electron source working in the adiabatic regime and emitting particles into a chiral electron waveguide. The noise power is found to be quadratic at low frequencies and exponentially suppressed at high frequencies.

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arXiv2013

Single-electron source: Adiabatic versus non-adiabatic emission

We investigate adiabatic and non-adiabatic emission of single particles into an edge state using an analytically solvable dynamical scattering matrix model of an on-demand source. We compare adiabatic and non-adiabatic emissions by considering two geometries: a collider geometry where two emitters are coupled to two different edge states and a series geometry where two emitters are coupled to the same edge state. Most effects observed for adiabatic emitters also occur for non-adiabatic emitters. In particular this applies to effects arising due to the overlap of wave-packets colliding at a quantum point contact. Specifically we compare the Pauli peak (the fermionic analog of the bosonic Hong-Ou-Mandel dip) for the adiabatic and non-adiabatic collider and find them to be similar. In contrast we find a striking difference between the two operating conditions in the series geometry in which particles are emitted into the same edge state. Whereas the squared average charge current can be nullified for both operating conditions, the heat current can be made to vanish only with adiabatic emitters.

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arXiv2012

Glauber coherence of single electron sources

Recently demonstrated solid state single electron sources generate different quantum states depending on their operation condition. For adiabatic and non-adiabatic sources we determine the Glauber correlation function in terms of the Floquet scattering matrix of the source. The correlation function provides full information on the shape of the state, on its time-dependent amplitude and phase, which makes the coherence properties of single electron states essential for the production of quantum multi-particle states.

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arXiv2011

Single-particle interference versus two-particle collisions

We consider a mesoscopic circuit in the quantum Hall effect regime comprising two synchronized single-particle sources emitting particles into a Mach-Zehnder interferometer. While particles from one source can possibly interfere at the interferometer output, particles from the second source are injected directly into one of the interferometer's arms and are used to create tunable and coherent suppression of interference. If particles from the two different sources collide at the interferometer output the magnetic-flux dependence of the charge transferred to one of the output contacts is suppressed. In contrast the interference pattern in the current at a fixed time is preserved and the impact of the second source manifests itself in a time-dependent phase-shift.

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arXiv2011

Coherence of Single Electron Sources from Mach-Zehnder Interferometry

A new type of electron sources has emerged which permits to inject particles in a controllable manner, one at a time, into an electronic circuit. Such single electron sources make it possible to fully exploit the particles' quantum nature. We determine the single-particle coherence length from the decay of the Aharonov-Bohm oscillations as a function of the imbalance of a Mach-Zehnder interferometer connected to a single electron source. The single-particle coherence length is of particular importance as it is an intrinsic property of the source in contrast to the dephasing length.

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arXiv2010

Spectroscopy of electron flows with single- and two-particle emitters

To analyze the state of injected carrier streams of different electron sources, we propose to use correlation measurements at a quantum point contact with the different sources connected via chiral edge states to the two inputs. In particular we consider the case of an on-demand single-electron emitter correlated with the carriers incident from a biased normal reservoir, a contact subject to an alternating voltage and a stochastic single electron emitter. The correlation can be viewed as a spectroscopic tool to compare the states of injected particles of different sources. If at the quantum point contact the amplitude profiles of electrons overlap, the noise correlation is suppressed. In the absence of an overlap the noise is roughly the sum of the noise powers due to the electron streams in each input. We show that the electron state emitted from a (dc or ac) biased metallic contact is different from a Lorentzian amplitude electron state emitted by the single electron emitter (a quantum capacitor driven with slow harmonic potential), since with these inputs the noise correlation is not suppressed. In contrast, if quantized voltage pulses are applied to a metallic contact instead of a dc (ac) bias then the noise can be suppressed. We find a noise suppression for multi-electron pulses and for the case of stochastic electron emitters for which the appearance of an electron at the quantum point contact is probabilistic.

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