arXiv subjects

Thomas Werkmeister

Publications and source records attributed to Thomas Werkmeister.

10 recordsLinked to original sources

arXiv2026

A scalable platform for nanometer-scale quantum confinement

Overcoming the limitations of current nanofabrication techniques to achieve nanoscale feature sizes is essential for achieving new regimes of light-matter interactions at extreme frequencies and length scales. Here, we demonstrate a scalable nanofabrication platform capable of producing in-plane feature sizes down to 1.75 nm, pushing the boundaries of current top-down nanofabrication techniques. Using precise thickness control of atomic layer deposition (ALD) and employing widely spaced oxide nanofins, we transform conventional ALD into a surface structuring method that produces nanolaminates with sub-10 nm periodicities over large areas. The resulting nanostructures can be used as a one-dimensional gate array to control charge carriers in two-dimensional materials. As an initial demonstration, we integrate the platform with graphene and perform electron transport measurements. In the presence of the gate array enabled by the nanolaminate, we observe satellite Dirac peaks consistent with band-structure modulation, suggestive of quantum-confinement effects. Our platform paves the way for exploring previously inaccessible regimes of nanoscale light-matter interactions, holding significant promise for applications in short wavelength optics, electronics, and polaritonics.

physics.optics↗

arXiv2026

Controlled localization of anyons in a graphene quantum Hall interferometer

Exchange statistics are a fundamental principle of quantum mechanics, dictating the symmetry of identical particle wavefunctions and thereby enabling emergent phenomena of many-body quantum states. The exchange-induced unitary transformation of both abelian and non-abelian anyonic wavefunctions can be probed using electronic fractional quantum Hall (FQH) interferometers, where quasiparticles propagating along the interfering FQH edge braid with those localized within the interferometer. Here, we add a gate-controlled dot/anti-dot in the center of a bilayer graphene FQH interferometer cavity to tune the number of enclosed anyons. We observe hundreds of controlled phase slips in the diagonal conductance across the interferometer for both abelian and non-abelian states, consistent with discrete changes in the localized quasiparticle population. For abelian anyons, the observed phase slips agree with the theoretically expected value. At half filling, our results suggest the interfering edge carries charge $|e^*/e| = 1/2$ abelian excitations, whereas charge $|e^*/e| = 1/4$ putative non-abelian anyons remain localized in the interferometer cavity. Controlling the population of localized $e/4$ anyons in an interferometer marks a significant milestone towards observing their non-local exchange statistics and building a fault tolerant topological qubit based on non-abelian anyon manipulation.

cond-mat.mes-hall↗

arXiv2026

Vortex-parity-controlled diode effect in Corbino topological Josephson junctions

Nonreciprocal supercurrents in Josephson junctions have recently emerged as a sensitive tool for investigating broken symmetries in superconducting quantum materials. Here, we report an even-odd Josephson diode effect (JDE) in Corbino-geometry junctions fabricated on the pristine surface of a bulk-insulating three-dimensional topological insulator (3DTI). We find that the diode polarity, which indicates the preferred direction of supercurrent flow, robustly alternates its sign depending on the parity (even or odd) of the enclosed vortex number. This behavior is absent in two key control devices: a non-topological graphene Corbino Josephson junction and a 3DTI-based linear Josephson junction. These results indicate that the polarity-tunable JDE is intrinsically linked to the unique combination of the proximitized topological superconductivity in the 3DTI surface and the Corbino device's closed-loop geometry. Our theoretical modeling attributes the observed sign change in diode polarity to the alternating sign of periodic boundary conditions in topological superconductors, supporting the interpretation that the vortex-parity-controlled JDE is a direct manifestation of the underlying Andreev bound state topology associated with the presence of non-Abelian anyons in the vortices.

cond-mat.supr-con↗

arXiv2026

Theory of reentrant superconductivity in Corbino Josephson junctions

Josephson junctions made of conventional superconductors display Fraunhofer-like oscillations of the critical current as a function of the threaded magnetic flux. When the superconductors are deposited on the surface of a three-dimensional topological insulator, this pattern is slightly modified due to the presence of chiral Majorana modes. Here we calculate the critical current of a Corbino Josephson junction, where the fluxoid becomes quantized and the superconducting phase has an integer winding. We discover that circular junctions exhibit similar behavior in both topologically trivial and non-trivial scenarios, while non-circular junctions demonstrate a remarkable distinction. Using a simple analytical model, we show that these non-circular junctions exhibit reentrant superconductivity with a period related to their number of corners, and numerically we find that this period is halved in the topological case. The period halving may help establish the existence of topological superconductivity in hybrid topological insulator-superconductor junctions.

cond-mat.mes-hall↗

arXiv2026

Kinetic Inductance of Few-Layer NbSe$_2$ in the Two-Dimensional Limit

Van der Waals (vdW) superconductors remain superconducting down to the monolayer limit, enabling the exploration of emergent physical phenomena and functionality driven by reduced dimensionality. Here, we report the characterization of the kinetic inductance of atomically thin NbSe$_2$, a two-dimensional van der Waals superconductor, using superconducting coplanar waveguides and microwave measurement techniques familiar to circuit quantum electrodynamics (cQED). The kinetic inductance scales inversely with the number of NbSe$_2$ layers, reaching 1.2 nH/$\Box$ in the monolayer limit. Furthermore, the measured kinetic inductance exhibits a thickness-dependent crossover from clean- to dirty-limit behavior, with enhanced dirty-limit contributions emerging in the ultra-thin regime. These effects are likely driven by increased surface scattering, multi-band superconductivity, and geometric confinement. Additionally, the self-Kerr nonlinearity of the NbSe$_2$ films ranges from $K/2π$ = -0.008 to -14.7 Hz/photon, indicating its strong potential in applications requiring compact, nearly linear, high-inductance superconducting quantum devices and detectors. The fabrication and characterization techniques demonstrated here are extensible to the investigation of other two-dimensional superconductors.

cond-mat.supr-con↗

arXiv2024

Anyon braiding and telegraph noise in a graphene interferometer

The search for anyons, quasiparticles with fractional charge and exotic exchange statistics, has inspired decades of condensed matter research. Quantum Hall interferometers enable direct observation of the anyon braiding phase via discrete interference phase jumps when the quasiparticle number changes. Here, we observe the universal anyonic braiding phase in both the $ν= 1/3$ and $4/3$ fractional quantum Hall states by probing three-state random telegraph noise (RTN) in real-time. We find that the observed RTN stems from anyon quasiparticle number $n$ fluctuations and reconstruct three Aharonov-Bohm oscillation signals phase shifted by $2π/3$, corresponding to the three possible interference branches from braiding around $n$ (mod 3) anyons. Hence, we fully characterize the anyon exchange statistics using new methods that can readily extend to non-abelian states.

cond-mat.mes-hall↗

arXiv2024

Task-Oriented Dialogue with In-Context Learning

We describe a system for building task-oriented dialogue systems combining the in-context learning abilities of large language models (LLMs) with the deterministic execution of business logic. LLMs are used to translate between the surface form of the conversation and a domain-specific language (DSL) which is used to progress the business logic. We compare our approach to the intent-based NLU approach predominantly used in industry today. Our experiments show that developing chatbots with our system requires significantly less effort than established approaches, that these chatbots can successfully navigate complex dialogues which are extremely challenging for NLU-based systems, and that our system has desirable properties for scaling task-oriented dialogue systems to a large number of tasks. We make our implementation available for use and further study.

cs.CL↗

arXiv2024

Strongly coupled edge states in a graphene quantum Hall interferometer

Electronic interferometers using the chiral, one-dimensional (1D) edge channels of the quantum Hall effect (QHE) can demonstrate a wealth of fundamental phenomena. The recent observation of phase jumps in a Fabry-Pérot (FP) interferometer revealed anyonic quasiparticle exchange statistics in the fractional QHE. When multiple integer edge channels are involved, FP interferometers have exhibited anomalous Aharonov-Bohm (AB) interference frequency doubling, suggesting putative pairing of electrons into 2e quasiparticles. Here, we use a highly tunable graphene-based QHE FP interferometer to observe the connection between interference phase jumps and AB frequency doubling, unveiling how strong repulsive interaction between edge channels leads to the apparent pairing phenomena. By tuning electron density in-situ from filling factor ν<2 to ν>7, we tune the interaction strength and observe periodic interference phase jumps leading to AB frequency doubling. Our observations demonstrate that the combination of repulsive interaction between the spin-split ν=2 edge channels and charge quantization is sufficient to explain the frequency doubling, through a near-perfect charge screening between the localized and extended edge channels. Our results show that interferometers are sensitive probes of microscopic interactions and enable future experiments studying correlated electrons in 1D channels using our highly tunable platform.

cond-mat.mes-hall↗

arXiv2024

Magneto-Thermoelectric Transport in Graphene Quantum Dot with Strong Correlations

Disorder at the etched edges of graphene quantum dots (GQD) enables random all-to-all interactions between localized charges in partially-filled Landau levels, providing a potential platform to realize the Sachdev-Ye-Kitaev (SYK) model. We use quantum Hall edge states in the graphene electrodes to measure electrical conductance and thermoelectric power across the GQD. We observe a rapid diminishing of electric conductance fluctuations and slowly decreasing thermoelectric power across the GQD with increasing temperature, consistent with recent theoretical predictions for the SYK regime.

cond-mat.mes-hall↗

arXiv2020

Aharonov Bohm Effect in Graphene Fabry Pérot Quantum Hall Interferometers

Quantum interferometers are powerful tools for probing the wave-nature and exchange statistics of indistinguishable particles. Of particular interest are interferometers formed by the chiral, one-dimensional (1D) edge channels of the quantum Hall effect (QHE) that guide electrons without dissipation. Using quantum point contacts (QPCs) as beamsplitters, these 1D channels can be split and recombined, enabling interference of charged particles. Such quantum Hall interferometers (QHIs) can be used for studying exchange statistics of anyonic quasiparticles. In this study we develop a robust QHI fabrication technique in van der Waals (vdW) materials and realize a graphene-based Fabry-Pérot (FP) QHI. By careful heterostructure design, we are able to measure pure Aharonov-Bohm (AB) interference effect in the integer QHE, a major technical challenge in finite size FP interferometers. We find that integer edge modes exhibit high visibility interference due to relatively large velocities and long phase coherence lengths. Our QHI with tunable QPCs presents a versatile platform for interferometer studies in vdW materials and enables future experiments in the fractional QHE.

cond-mat.mes-hall↗