arXiv subjects

Stijn R. de Wit

Publications and source records attributed to Stijn R. de Wit.

5 recordsLinked to original sources

arXiv2026

Manipulating the topological spin of Majoranas

The non-Abelian exchange statistics of Majorana zero modes make them interesting for both technological applications and fundamental research. Unlike their non-Abelian counterpart, the Abelian contribution, $e^{iθ}$, where $θ$ is directly related to the Majorana's topological spin, is often neglected. However, the Abelian exchange phase and hence the topological spin can differ from system to system. For vortices in topological superconductors, the Abelian exchange phase is interpreted as an Aharonov-Casher phase arising from a vortex encircling a $e/4$ charge. In this work, we show how this fractional charge, and hence the topological spin, can be manipulated through the control of device geometry, introducing an additional control knob for topological quantum computing. To probe this effect, we propose a vortex interference experiment that reveals the presence of this fractional charge through shifts in the critical current.

cond-mat.mes-hall↗

arXiv2026

Coexisting topological hinges and 1D Rashba states in Bi$_{0.97}$Sb$_{0.03}$ revealed by the Josephson effect

Second-order topological insulating (SOTI) states in three-dimensional materials are helical one-dimensional hinge states. Inducing superconductivity in these states leads to gapless bound states, characterized by the 4$π$-periodic current-phase relation. Here, we provide evidence of the topologically protected hinge states in Dirac semimetal Bi$_{0.97}$Sb$_{0.03}$ nanoflakes by an unconventional interference pattern in a magnetic field, and the 4$π$-periodic supercurrent carried by these states via the suppressed first and third Shapiro steps. Tight-binding simulations confirm the presence of multiple hinge modes, supporting our interpretation of Bi$_{0.97}$Sb$_{0.03}$ as a prototypical designable SOTI platform. Quantum confinement effect is identified by a quasi-one-dimensional bulk transport, and the confined Rashba states are responsible for the broadened hinge states.

cond-mat.mes-hall↗

arXiv2025

Observation of the surface hybridization gap in the electrical transport properties of the ultrathin topological insulator (Bi$_{1-x}$Sb$_{x}$)$_2$Te$_3$

We study the three-dimensional topological insulator (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ in its ultrathin limit i.e. when the thickness is of the same order as the surface state penetration depth. It is expected that in this limit a hybridization gap opens at the Dirac point, which gives rise to a quantum spin Hall (QSH) or insulating phase, depending on the material thickness. We fabricate (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ Hall bars with a thicknesses of 6 and 9 nm and measure an insulating phase around the Dirac point for low bias and at sub-Kelvin temperatures only in samples fabricated from the 6 nm films, which indicates the presence of a hybridization gap. The effect of a perpendicular magnetic field on the hybridization gap is studied but remains partially unresolved. The results form an important step towards experimentally realizing the quantum spin Hall state via hybridization in ultrathin films of (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$, yet, they also expose a knowledge gap regarding transport measurements in these systems.

cond-mat.mes-hall↗

arXiv2023

A many-body singlet prepared by a central spin qubit

Controllable quantum many-body systems are platforms for fundamental investigations into the nature of entanglement and promise to deliver computational speed-up for a broad class of algorithms and simulations. In particular, engineering entanglement within a dense spin ensemble can turn it into a robust quantum memory or a computational platform. Recent experimental progress in dense central spin systems motivates the design of algorithms that use a central-spin qubit as a convenient proxy for the ensemble. Here we propose a protocol that uses a central spin to initialize two dense spin ensembles into a pure anti-polarized state and from there creates a many-body entangled state -- a singlet -- from the combined ensemble. We quantify the protocol performance for multiple material platforms and show that it can be implemented even in the presence of realistic levels of decoherence. Our protocol introduces an algorithmic approach to preparation of a known many-body state and to entanglement engineering in a dense spin ensemble, which can be extended towards a broad class of collective quantum states.

quant-ph↗

arXiv2023

Multiple Andreev reflections in two-dimensional Josephson junctions with broken time-reversal symmetry

Andreev bound states (ABS) occur in Josephson junctions when the total phase of the Andreev and normal reflections is a multiple of $2π$. In ballistic junctions with an applied voltage bias, a quasi-particle undergoes multiple Andreev reflections before entering the leads, resulting in peaks in the current-voltage $I(V)$ curve. Here we present a general model for Josephson junctions with spin-active interlayers i.e., magnetic or topological materials with broken time-reversal symmetry. We investigate how ABS change the peak positions and shape of $I(V)$, which becomes asymmetric for a single incident angle. We show how the angle-resolved $I(V)$ curve becomes a spectroscopic tool for the chirality and degeneracy of ABS.

cond-mat.supr-con↗