arXiv subjects

Eric Kleinherbers

Publications and source records attributed to Eric Kleinherbers.

17 recordsLinked to original sources

arXiv2025

Breaking conservation law enables steady-state entanglement out of equilibrium

We show how entangled steady states can be prepared by purely dissipative dynamics in a system coupled to a thermal environment. While entanglement is hindered by thermalization when the system and environment exchange a conserved quantity, we demonstrate that breaking this conservation law through the system-environment interaction drives the system to a nonequilibrium steady state. Such an interaction will generate multiple competing equilibration channels, effectively mimicking baths at distinct chemical potentials. When the environment also supports long-range correlations, these channels mediate nonlocal dissipation capable of generating entanglement. We illustrate the scheme in a model of two nitrogen-vacancy (NV) centers weakly coupled to a spin-pumped magnet, where tuneable magnon excitations enable steady-state entanglement over finite distances. Our results identifies a general mechanism for dissipative entanglement generation, rooted in the conservation structure and environmental correlations rather than fine-tuned coherent control or active driving.

quant-ph↗

arXiv2025

Topological hydrodynamics in spin-triplet superconductors

Due to the structure of the underlying SO(3) $\mathbf d$-vector order parameter, spin triplet superconductors exhibit a bulk-edge correspondence linking the circulation of supercurrent to the bulk magnetic skyrmion density, giving rise to topological hydrodynamics of magnetic skyrmions. To probe the interplay of charge and spin dynamics, we propose a blueprint for a spin-triplet superconducting quantum interference device (SQUID), which functions without a Josephson weak link. The triplet SQUID undergoes nonsingular $4\pi$ phase slips, in which current relaxation is facilitated by spin dynamics that trace out a magnetic skyrmion texture. Inductively coupling the device to a tank circuit and probing the nonlinear supercurrent response via Oersted field measurements could provide an experimental signature of ferromagnetic spin-triplet superconductivity.

cond-mat.mes-hall↗

arXiv2025

Entangling color centers via magnon-antimagnon pair creation

We present how entanglement between a spatially separated pair of color centers can be created by letting them weakly interact with the quantum fluctuations of a nonequilibrium magnetic environment. To this end, we consider two coupled ferromagnets, one in the ground state and one in an inverted state with respect to an applied magnetic field. The resulting energetic instability leads to a quantum spin current in the vacuum state that is sustained by the creation of magnon-antimagnon pairs at the interface. We show that these quantum fluctuations imprint a steady-state entanglement onto the two dipole-coupled color centers through nonlocal dissipation. We derive conditions for establishing a maximally entangled Bell state. This entanglement is absent in thermal equilibrium.

cond-mat.mes-hall↗

arXiv2025

Correlated emission of electron-current waves

Correlated emission of light offer a potential avenue for entanglement generation between atomic spins, with potential application for sensing and quantum memory. In this work, we investigate the conditions for the correlated emission by color centers into an electronic bath of conduction electrons. Unlike emission into bosonic modes, electrons can absorb energy via two-particle processes across a large range of length scales. We find that two length scales are particularly relevant: one set by the Fermi velocity and the frequency of the color centers $v_F/Δ$, and the other set by the Fermi wavelength $λ_F \ll v_F/Δ$. Subradiance requires emitters to be spaced at a distance closer than the Fermi wavelength, while superradiance requires spacing less than $\sqrt{λ_F v_F/Δ}$, so long as the emitters are initialized with coherence. We show that the emitted current burst has a spiral form, and we discuss the experimental possibility to observe correlated dissipation by color-center qubits coupled to electronic environments.

quant-ph↗

arXiv2025

Topological transport of vorticity on curved magnetic membranes

In this work, we study the transport of vorticity on curved dynamical two-dimensional magnetic membranes. We find that topological transport can be controlled by geometrically reducing symmetries, enabling processes absent from flat magnetic systems. To this end, the vorticity 3-current is constructed, which obeys a continuity equation immune to local disturbances of the magnetic texture and spatiotemporal fluctuations of the membrane. We show how electric current can manipulate vortex transport in geometrically nontrivial magnetic systems. As an illustrative example, we propose a minimal setup that realizes an experimentally feasible energy storage device and discuss its thermodynamic efficiency in terms of a vortexoelectric counterpart of the thermoelectric figure of merit $ZT$.

cond-mat.mes-hall↗

arXiv2025

Effective time-dependent temperature for fermionic master equations beyond the Markov and the secular approximations

We consider a fermionic quantum system exchanging particles with an environment at a fixed temperature and study its reduced evolution by means of a Redfield-I equation with time-dependent (non-Markovian) coefficients. We find that the description can be efficiently reduced to a standard-form Redfield-II equation, however, with a time-dependent effective bath temperature obeying a universal law. At early times, after the system and environment start in a product state, the effective temperature appears to be very high, yet eventually it settles down towards the true environment value. In this way, we obtain a time-local master equation, offering high accuracy at all times and preserving the crucial properties of the density matrix. It includes non-Markovian relaxation processes beyond the secular approximation and time-averaging methods and can be further applied to various types of Gorini-Kossakowski-Sudarshan-Lindblad equations. We derive the theory from first principles and discuss its application using a simple example of a single quantum dot.

cond-mat.mes-hall↗

arXiv2025

Proposal for spin superfluid quantum interference device

In easy-plane magnets, the spin superfluid phase was predicted to facilitate coherent spin transport. So far, experimental evidence remains elusive. In this Letter, we propose an indirect way to sense this effect via the spin superfluid quantum interference device (spin SQUID), inspired by its superconducting counterpart (rf SQUID). The spin SQUID is constructed as a quasi-one-dimensional (1D) magnetic ring with a single Josephson weak link, functioning as an isolated device with a microwave response. The spin current is controlled by an in-plane electric field through Dzyaloshinskii-Moriya interaction. This interaction can be interpreted as a gauge field that couples to the spin supercurrent through the Aharonov-Casher effect. By investigating the static and dynamic properties of the device, we show that the spin current and the harmonic frequencies of the spin superfluid are periodic with respect to the accumulated Aharonov-Casher phase and are, therefore, sensitive to the radial electric flux through the ring in units of an electric flux quantum, suggesting a potential electric-field sensing functionality. For readout, we propose to apply spectroscopic analysis to detect the frequency shift of the harmonic modes induced by this magnonic Stark effect.

cond-mat.mes-hall↗

arXiv2024

Dark versus blocking states in electronic transport: a Lee-Yang zero analysis of full counting statistics

Electronic transport through nanostructures can be suppressed by coherent population trapping, in which quantum coherence leads to a dark state that decouples from the drain electrode. Finite transport, then, relies on decoherence of the dark state. An alternative scenario for reduced transport is weak coupling of a state, referred to as a blocking state, to the drain. This raises the question of whether and how these two scenarios can be distinguished in the transport features. For the example of electron transport through a carbon nanotube, we identify regimes, in which this distinction is possible by analyzing the full counting statistics in terms of Lee-Yang zeros and factorial cumulants.

cond-mat.mes-hall↗

arXiv2024

Magnon kinetic theory of the antiferromagnetic Hanle effect

Motivated by the recently discovered magnonic Hanle effect in an insulating antiferromagnet [Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)], we develop a spin transport theory based on low-energy waves of antiferromagnetic Néel order. These waves have two polarizations, which we describe in analogy to optics using the Stokes vector on the Poincaré sphere. We find that the polarization, which encodes the magnon spin angular momentum, changes periodically with a frequency that is nonlinear in the magnetic field. This explains the observed asymmetry in the Hanle signal as a function of the magnetic field, along with other salient experimental features. By providing an energy-resolved description of the spin injection, our theory combines the kinetic transport of magnons with the coherent dynamics of their polarization in an intuitive way. This opens a general perspective on a coherent control of magnonic spin density in collinear antiferromagnets.

cond-mat.mes-hall↗

arXiv2023

Electronic transport in bent carbon nanotubes

We study the electronic transport through uniformly bent carbon nanotubes. For this purpose, we describe the nanotube with the tight-binding model and calculate the local current flow by employing non-equilibrium Green's functions (NEGF) in the Keldysh formalism. In addition, we describe the low-energy excitations using an effective Dirac equation in curved space with a strain-induced pseudo-magnetic field which can be solved analytically for the torus geometry in terms of the Mathieu functions. We obtain a perfect quantitative agreement with the NEGF results. For nanotubes with an armchair edge, already a weak bending of 1% substantially changes the electronic properties. Depending on the valley, the current of the zero mode flows either on the outer or the inner side of the torus and, therefore, can be used as a valley splitter. In contrast, the zigzag nanotubes are largely unaffected by the bending. Our findings are of importance for nanoelectronic applications of carbon nanotubes and open new possibilities for valleytronics.

cond-mat.mes-hall↗

arXiv2023

Unraveling spin dynamics from charge fluctuations

The use of single electron spins in quantum dots as qubits requires detailed knowledge about the processes involved in their initialization and operation as well as their relaxation and decoherence. In optical schemes for such spin qubits, spin-flip Raman as well as Auger processes play an important role, in addition to environment-induced spin relaxation. In this paper, we demonstrate how to quantitatively access all the spin-related processes in one go by monitoring the charge fluctuations of the quantum dot. For this, we employ resonance fluorescence and analyze the charge fluctuations in terms of waiting-time distributions and full counting statistics characterized by factorial cumulants.

cond-mat.mes-hall↗

arXiv2023

Full counting statistics in a Majorana single-charge transistor

We study full counting statistics of electron transport through a Majorana single-charge transistor. At low bias voltage, transport is dominated by the so-called Josephson-Majorana cycle, a sequence of normal and anomalous single-charge and Josephson tunneling. Factorial cumulants characterizing the full counting statistics elucidate the correlated nature of the charge transfers in this cycle. Moreover, we predict a topological transition in the full counting statistics from a perfect Poissonian transfer of Cooper pairs to a correlated switching between two distinct fermion parity states with increasing Josephson coupling.

cond-mat.mes-hall↗

arXiv2022

Pushing the limits in real-time measurements of quantum dynamics

Time-resolved studies of quantum systems are the key to understand quantum dynamics at its core. The real-time measurement of individual quantum numbers as they switch between certain discrete values, well known as random telegraph signal, is expected to yield maximal physical insight. However, the signal suffers from both systematic errors, such as a limited time resolution and noise from the measurement apparatus, as well as statistical errors due to a limited amount of data. Here we demonstrate that an evaluation scheme based on factorial cumulants can reduce the influence of such errors by orders of magnitude. The error resilience is supported by a general theory for the detection errors as well as experimental data of single-electron tunnelling through a self-assembled quantum dot. Thus, factorial cumulants push the limits in the analysis of random telegraph data which represent a wide class of experiments in physics, chemistry, engineering and life sciences.

cond-mat.mes-hall↗

arXiv2021

Post-processing of real-time quantum event measurements for an optimal bandwidth

Single electron tunneling and its transport statistics have been studied for some time using high precision charge detectors. However, this type of detection requires advanced lithography, optimized material systems and low temperatures (mK). A promising alternative, recently demonstrated, is to exploit an optical transition that is turned on or off when a tunnel event occurs. High bandwidths should be achievable with this approach, although this has not been adequately investigated so far. We have studied low temperature resonance fluorescence from a self-assembled quantum dot embedded in a diode structure. We detect single photons from the dot in real time and evaluate the recorded data only after the experiment, using post-processing to obtain the random telegraph signal of the electron transport. This is a significant difference from commonly used charge detectors and allows us to determine the optimal time resolution for analyzing our data. We show how this post-processing affects both the determination of tunneling rates using waiting-time distributions and statistical analysis using full-counting statistics. We also demonstrate, as an example, that we can analyze our data with bandwidths as high as 350 kHz. Using a simple model, we discuss the limiting factors for achieving the optimal bandwidth and propose how a time resolution of more than 1 MHz could be achieved.

cond-mat.mes-hall↗

arXiv2021

Synchronized coherent charge oscillations in coupled double quantum dots

We study coherent oscillations in double quantum dots tunnel-coupled to metallic leads by means of full counting statistics of electron transport. If two such systems are coupled by Coulomb interaction, there are in total six (instead of only two) oscillation modes of the entangled system with interaction-dependent oscillation frequencies. By tuning the bias voltage, one can engineer decoherence such that only one of the six modes, in which the charge oscillations in both double quantum dots become synchronized in antiphase, is singled out. We suggest to use waiting-time distributions and the $g^{(2)}$-correlation function to detect the common frequency and the phase locking.

cond-mat.mes-hall↗

arXiv2020

Relaxation dynamics in a Hubbard dimer coupled to fermionic baths: phenomenological description and its microscopic foundation

We study relaxation dynamics in a strongly-interacting two-site Fermi-Hubbard model that is induced by coupling each site to a local fermionic bath. To derive the proper form of the Lindblad operators that enter an effective description of the system-bath coupling in different temperature regimes, we employ a diagrammatic real-time technique for the time evolution of the reduced density matrix. In spite of a local coupling to the baths, the found Lindblad operators are non-local in space. We compare with the local approximation, where those non-local effects are neglected. Furthermore, we propose an improvement on the commonly-used secular approximation (rotating-wave approximation), referred to as coherent approximation, which turns out superior in all studied parameter regimes (and equivalent otherwise). We look at the relaxation dynamics for several important observables and compare the methods for early and late times in various temperature regimes.

cond-mat.str-el↗

arXiv2018

Revealing attractive electron-electron interaction in a quantum dot by full counting statistics

Recent experiments [Nature 521, 196 (2015) and Nat. Commun. 8, 395 (2017)] have presented evidence for electron pairing in a quantum dot beyond the superconducting regime. Here, we show that the impact of an attractive electron-electron interaction on the full counting statistics of electron transfer through a quantum dot is qualitatively different from the case of a repulsive interaction. In particular, the sign of higher-order (generalized) factorial cumulants reveals more pronounced correlations, which even survive in the limit of fast spin relaxation.

cond-mat.mes-hall↗