arXiv subjects

Devashish Shah

Publications and source records attributed to Devashish Shah.

4 recordsLinked to original sources

arXiv2026

Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices

In superconductor-semiconductor hybrid structures, superconductivity and spin polarization are competing effects as magnetic fields break Cooper pairs. They can be combined using thin films and in-plane magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev spin qubits (ASQs), but remains challenging for materials with small in-plane $g$-factors or when out-of-plane fields are required. We demonstrate that granular aluminium (grAl), composed of nanometre-scale aluminium grains embedded in an amorphous oxide matrix, can overcome this limitation. By depositing grAl on Ge/SiGe heterostructures, we induce a hard superconducting gap with BCS peaks at $305~\mu\mathrm{eV}$ and magnetic-field resilience for both the in-plane and out-of-plane directions, allowing Zeeman splitting of Yu-Shiba-Rusinov (YSR) states beyond $50~\mu\mathrm{eV}$ (12 GHz). Leveraging this robustness, we reveal signatures of hole physics and discuss a driving mechanism for ASQs regardless of the strength of the Rashba spin-orbit coupling in planar germanium.

cond-mat.mes-hall↗

arXiv2025

Full Shapiro spectroscopy of current-phase relationships

Extracting the current-phase relationship (CPR) of a single superconducting junction is challenging in practice and traditionally involves embedding the junction in a larger superconducting circuit containing SQUIDs and/or resonators. Applying ac driving to the junction has proven to be a viable and less invasive way to extract information about the few lowest harmonics of the CPR, by locating the integer and fractional Shapiro steps in the IV-curve of the driven junction. Here, we present an alternative driving-based method that allows to extract the full harmonic content of a CPR in a non-invasive way, by fitting the measured critical currents of the driven junction as a function of driving power. We test our method, both using numerical simulations and in experiments, and we show that it works very accurately, also in the presence of noise.

cond-mat.supr-con↗

arXiv2024

Preserving Coulomb blockade in transport spectroscopy of quantum dots, by dynamical tunnel-barrier compensation

Surface-gated quantum dots (QDs) in semiconductor heterostructures represent a highly attractive platform for quantum computation and simulation. However, in this implementation, the barriers through which the QD is tunnel-coupled to source and drain reservoirs (or neighboring QDs) are usually non-rigid, and capacitively influenced by the plunger gate voltage (VP). In transport spectroscopy measurements, this leads to complete suppression of current and lifting of Coulomb blockade, for large negative and positive values of VP, respectively. Consequently, the charge-occupancy of the QD can be tuned over a rather small range of VP. By dynamically tuning the tunnel barriers to compensate for the capacitive effect of VP, here we demonstrate a protocol which allows the Coulomb blockade to be preserved over a remarkably large span of charge-occupancies, as demonstrated by clean Coulomb diamonds and well-resolved excited state features. The protocol will be highly beneficial for automated tuning and identification of the gatevoltage-space for optimal operation of QDs, in large arrays required for a scalable spin quantum computing architecture.

cond-mat.mes-hall↗

arXiv2024

Measurement of electromagnetic radiation force using a capacitance-bridge interferometer

We present a mechanical cantilever-based tabletop interferometer to measure the radiation force exerted by light. Using a high-power (~ 1W) pulsed laser beam, we excite mechanical oscillations in a thin metallic cantilever. The cantilever forms a parallel-plate capacitor with a printed circuit board trace. Using a capacitance-bridge geometry, we measure small capacitance changes of the order of femto-farads, induced by the radiation forces of a few nano-newtons. This experiment uses equipment commonly found in an undergraduate teaching laboratory for physics and electronics while providing insight into electromagnetic wave theory, circuit design for low-noise measurements, and Fourier analysis.

physics.ed-ph↗