arXiv subjects

Timo Wagner

Publications and source records attributed to Timo Wagner.

7 recordsLinked to original sources

arXiv2026

Geometry-Induced Transport of Self-Aligning Chiral Bristlebots

Active matter systems characterized by the interplay of chirality and self-alignment offer a rich landscape for non-equilibrium collective behaviors and the development of autonomous materials. We present a versatile experimental platform for studying these dynamics using augmented commercial bristlebots, where custom-designed housings and elastic couplings induce a self-aligning torque and stable chiral drift. By mapping experimental trajectories to a Langevin-type model, we characterize the single-particle dynamics. In circular geometries, we show that the stability of edge currents is governed by the interaction between intrinsic particle chirality and handedness of the edge current. Furthermore, we demonstrate that transport can be geometrically rectified using a nautilus-shaped obstacle acting as a doubly chirality-sensitive ratchet. Finally, we explore the collective dynamics of rigidly linked assemblies, observing spontaneous mode-switching between translational and rotational states in active solids. Our results provide a robust framework for experimental studies in active gases and illustrate how geometric constraints can be used to program complex transport properties in active systems.

cond-mat.soft↗

arXiv2025

Interplay between Hund's rule and Kondo effect in a quantum dot

The interaction between localized spins on a quantum dot and free electrons in the reservoirs forms a many-particle entangled system giving rise to the Kondo effect. Here, we investigate electron transport in the third shell of a gate-defined GaAs quantum dot. The addition energy shows a maximum at half-filling of the shell which can be described analytically with Hund's rule exchange interaction. For 7 to 11 electrons occupying the quantum dot Zero-bias anomalies characteristic for the Kondo effect are observed, but with unexpected widths. Here the quantum dot has to be described as a multi-orbital Kondo impurity with Hund's interaction. In this way this quantum dot can be seen as a model system for a Hund's coupled mixed-valence quantum impurity as appearing in Hund's metals where local ferromagnetic interactions between orbitals lead to the emergence of complex electronic states.

cond-mat.mes-hall↗

arXiv2024

Real-Time Detection and Control of Correlated Charge Tunneling in a Quantum Dot

We experimentally demonstrate the real-time detection and control of correlated charge tunneling in a dynamically driven quantum dot. Specifically, we measure the joint distribution of waiting times between tunneling charges and show that the waiting times for holes may be strongly correlated due to the periodic drive and the Coulomb interactions on the dot, although the electron waiting times are not. Our measurements are in excellent agreement with a theoretical model that allows us to develop a detailed understanding of the correlated tunneling events. We also demonstrate that the degree of correlations can be controlled by the drive. Our experiment paves the way for systematic real-time investigations of correlated electron transport in low-dimensional nanostructures.

cond-mat.mes-hall↗

arXiv2020

Spectral properties of stochastic resonance in quantum transport

We investigate theoretically and experimentally stochastic resonance in a quantum dot coupled to electron source and drain via time-dependent tunnel barriers. A central finding is a transition visible in the current noise spectrum as a bifurcation of a dip originally at zero frequency. The transition occurs close to the stochastic resonance working point and relates to quantized pumping. For the evaluation of power spectra from measured waiting times, we generalize a result from renewal theory to the ac driven case. Moreover, we develop a master equation method to obtain phase-averaged current noise spectra for driven quantum transport.

cond-mat.mes-hall↗

arXiv2020

Controlled emission time statistics of a dynamic single-electron transistor

Quantum technologies involving qubit measurements based on electronic interferometers rely critically on accurate single-particle emission. However, achieving precisely timed operations requires exquisite control of the single-particle sources in the time domain. Here, we demonstrate accurate control of the emission time statistics of a dynamic single-electron transistor by measuring the waiting times between emitted electrons. By ramping up the modulation frequency, we controllably drive the system through a crossover from adiabatic to nonadiabatic dynamics, which we visualize by measuring the temporal fluctuations at the single-electron level and explain using detailed theory. Our work paves the way for future technologies based on the ability to control, transmit, and detect single quanta of charge or heat in the form of electrons, photons, or phonons.

cond-mat.mes-hall↗

arXiv2014

Partitioning of on-demand electron pairs

We demonstrate the high fidelity splitting of electron pairs emitted on demand from a dynamic quantum dot by an electronic beam splitter. The fidelity of pair splitting is inferred from the coincidence of arrival in two detector paths probed by a measurement of the partitioning noise. The emission characteristic of the on-demand electron source is tunable from electrons being partitioned equally and independently to electron pairs being split with a fidelity of 90%. For low beam splitter transmittance we further find evidence of pair bunching violating statistical expectations for independent fermions.

cond-mat.mes-hall↗

arXiv2013

Induced Superconductivity in the Quantum Spin Hall Edge

Topological insulators are a newly discovered phase of matter characterized by a gapped bulk surrounded by novel conducting boundary states. Since their theoretical discovery, these materials have encouraged intense efforts to study their properties and capabilities. Among the most striking results of this activity are proposals to engineer a new variety of superconductor at the surfaces of topological insulators. These topological superconductors would be capable of supporting localized Majorana fermions, particles whose braiding properties have been proposed as the basis of a fault-tolerant quantum computer. Despite the clear theoretical motivation, a conclusive realization of topological superconductivity remains an outstanding experimental goal. Here we present measurements of superconductivity induced in two-dimensional HgTe/HgCdTe quantum wells, a material which becomes a quantum spin Hall insulator when the well width exceeds d_{C}=6.3 nm. In wells that are 7.5 nm wide, we find that supercurrents are confined to the one-dimensional sample edges as the bulk density is depleted. However, when the well width is decreased to 4.5 nm the edge supercurrents cannot be distinguished from those in the bulk. These results provide evidence for superconductivity induced in the helical edges of the quantum spin Hall effect, a promising step toward the demonstration of one-dimensional topological superconductivity. Our results also provide a direct measurement of the widths of these edge channels, which range from 180 nm to 408 nm.

cond-mat.mes-hall↗