arXiv subjects

Karina Hudson

Publications and source records attributed to Karina Hudson.

4 recordsLinked to original sources

arXiv2026

Buried unstrained germanium channels: a lattice-matched platform for quantum technology

Strained Ge ($ε$-Ge) and strained Si ($ε$-Si) buried quantum wells have enabled advanced spin-qubit quantum processors. However, in the absence of suitable lattice-matched substrates, $ε$-Ge and $ε$-Si are deposited on defective, metamorphic SiGe substrates, which may impact device performance and scaling. Here an alternative platform is introduced, based on the heterojunction between unstrained Ge and a lattice-matched strained SiGe ($ε$-SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52-nm-thick $ε$-SiGe barrier, a low-disorder two-dimensional hole gas is demonstrated with a high-mobility of 1.33$\times$10$^5$ cm$^2$/Vs and a low percolation density of 1.4(1)$\times$10$^1$$^0$ cm$^-$$^2$. Quantum transport shows that holes confined in the buried unstrained Ge channel have a strong density-dependent in-plane effective mass and out-of-plane $g$-factor, pointing to a significant heavy-hole$-$light-hole mixing in agreement with theory. Measurements of Zeeman spin-split levels in quantum point contacts further highlight this character, showing a two-fold larger in-plane $g$-factor in Ge than in $ε$-Ge. The prospect of strong spin-orbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.

cond-mat.mes-hall↗

arXiv2025

Conductance Plateaus at Quantum Hall Integer Filling Factors in Germanium Quantum Point Contacts

Constricting transport through a one-dimensional quantum point contact in the quantum Hall regime enables gate-tunable selection of the edge modes propagating between voltage probe electrodes. Here we investigate the quantum Hall effect in a quantum point contact fabricated on low disorder strained germanium quantum wells. For increasing magnetic field, we observe Zeeman spin-split 1D ballistic hole transport evolving to integer quantum Hall states, with well-defined quantised conductance increasing in multiples of $e^2/h$ down to the first integer filling factor $ν=1$. These results establish strained germanium as a viable platform for complex experiments probing many-body states and quantum phase transitions.

cond-mat.mes-hall↗

arXiv2025

QARPET: A Crossbar Chip for Benchmarking Semiconductor Spin Qubits

Large-scale integration of semiconductor spin qubits into quantum processors hinges on the ability to characterize quantum components at scale, a task challenged by their operation at sub-kelvin temperatures, in the presence of magnetic fields, and by the use of radio-frequency signals. Here, we present QARPET (Qubit-Array Research Platform for Engineering and Testing), a scalable architecture for characterizing spin qubits using a quantum dot crossbar array. The crossbar features tightly-pitched spin qubit tiles and is implemented in planar germanium, by fabricating a large device with the potential to host 1058 hole spin qubits. Measurements on a patch of 40 tiles demonstrate key device functionality at millikelvin temperatures, including tile addressability, threshold voltage and charge noise statistics, and the characterisation of hole spin qubits and their coherence times in a single tile. These demonstrations pave the way for a new generation of quantum devices designed for the statistical characterisation of spin qubits.

cond-mat.mes-hall↗

arXiv2022

Observation of oscillating $g$-factor anisotropy arising from strong crystal lattice anisotropy in GaAs spin-3/2 hole quantum point contacts

Many modern spin-based devices rely on the spin-orbit interaction, which is highly sensitive to the host semiconductor heterostructure and varies substantially depending on crystal direction, crystal asymmetry (Dresselhaus), and quantum confinement asymmetry (Rashba). One-dimensional quantum point contacts are a powerful tool to probe both energy and directional dependence of spin-orbit interaction through the effect on the hole $g$-factor. In this work we investigate the role of cubic crystal asymmetry in driving an oscillation in the in-plane hole $g$-factor anisotropy when the quantum point contact is rotated with respect to the crystal axes, and we are able to separate contributions to the Zeeman Hamiltonian arising from Rashba and cubic crystal asymmetry spin-orbit interactions. The in-plane $g$-factor is found to be extremely sensitive to the orientation of the quantum point contact, changing by a factor of $5$ when rotated by $45^{\circ}$. This exceptionally strong crystal lattice anisotropy of the in-plane Zeeman splitting cannot be explained within axially symmetric theoretical models. Theoretical modelling based on the combined Luttinger, Rashba and Dresselhaus Hamiltonians that we use here reveals new spin-orbit contributions to the in-plane hole $g$-factor and provides an excellent agreement with our experimental data.

cond-mat.mes-hall↗