Readout of small-scale semiconductor spin-qubit arrays

Anasua Chatterjee,  Niels Bohr Institute, University of Copenhagen, Denmark

The engineering of readout methods becomes crucial as single qubits are scaled up in linear and two-dimensional arrays. In particular, fast, high-fidelity and simultaneous measurements across these small arrays are essential. I will present our work on readout techniques and scaling efforts, in particular involving RF-reflectometry, in small two-dimensional arrays of quantum dots in GaAs and silicon. In these systems we utilize techniques such as crosstalk mitigation, multi-qubit DC and pulse calibration, sensor compensation, virtual gates, and adaptive searching in high-dimensional spaces. These methods, combined with pulsed-gate techniques, enable deterministic single-electron shuttling within the array, and may be beneficial for many other quantum-dot devices or spin- and charge-based hybrid systems.

Unravelling properties of Brown-Zak fermions at ultra-low temperatures

Julien Barrier, University of Manchester, UK

In quantising magnetic fields, graphene superlattices exhibit a complex fractal spectrum often referred to as the Hofstadter butterfly. It can be viewed as a collection of Landau levels that arise from quantization of Brown-Zak minibands recurring at rational (p/q) fractions of the magnetic flux quantum per superlattice unit cell. I will show that, in graphene-on-boron-nitride superlattices, Brown-Zak fermions can exhibit mobilities above 106 cm2 V-1 s-1 and the mean free path exceeding several micrometres. High resolution measurements and high quality devices allow us to show that Brown-Zak minibands are 4q times degenerate and all the degeneracies (spin, valley and mini-valley) can be lifted by exchange interactions below 1 K. Moreover, in some parts of the Hofstadter spectrum, Landau levels exhibit nonlinear and staircase-like features that cannot be explained within a single-particle picture.

Angular-dependent magnetoresistance in topological semimetal PtBi2

Beilun Wu, Autonomous University of Madrid, Spain

Recently, extremely-large, non-saturating magnetoresistance observed in many semi-metallic compounds has aroused great discussion. In some cases, the magnetoresistance reveals a puzzling linear behavior, whose origin is under debate. Here we present angular-dependent magnetoresistance studies up to 22 Tesla in a topologically non-trivial semimetal PtBi2. The measurements have been performed with the help of an Oxford 20+2 T superconducting magnet. We show through systematic angular-dependent magnetotransport and Shubnikov-de Haas quantum oscillations measurements, that a perfect linear magnetoresistance appearing at one specific field angle in this system comes from the presence of open orbits. I will also present some first images made at 20 T using a new Scanning Tunneling Microscope and some data on a pnictide superconductor.

Quantum computing and qubit scale-up applications with Proteox

James Robinson, Product Manager, Oxford Instruments, UK

This webinar provides an overview of the new Proteox dilution refrigerator from Oxford Instruments, highlighting the key features and suitability for many quantum computing and qubit scale-up applications. The Proteox system is an essential tool for low temperature researchers, providing advanced research capability. It enables a step change in Cryofree system modularity, designed for enhanced adaptability, reliability and increased experimental capacity. If you are dealing with low temperature experiments, don’t miss this webinar.