Superconducting gatemon qubit based on a proximitized two-dimensional electron gas

Abstract

The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting circuits, from setting qubit transition frequencies and interqubit coupling strengths to the gain of parametric amplifiers for quantum-limited readout. The inductance is either set by tailoring the metal oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant that employs locally gated nanowire superconductor-semiconductor JJs for qubit control. Here we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show that 2DEG gatemons meet the requirements by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 μs, limited by dielectric loss in the 2DEG substrate.

Evidence of topological superconductivity in planar Josephson junctions

“…The phase and magnetic field dependence of the zero-energy states is consistent with a model of Majorana zero modes in finite-size Josephson junctions. Besides providing experimental evidence of phase-tuned topological superconductivity, our devices are compatible with superconducting quantum electrodynamics architectures [11] and scalable to complex geometries needed for topological quantum computing [9,12].…”

Supercurrent interference in semiconductor nanowire Josephson junctions

“…We observe in Fig. 7(a) that the critical current does not monotonically decrease to zero, particularly for Φ ∈ [3,4]. The appearance of these small oscillations is due to the interference with the quasiparticles normally reflected from the N/S interfaces.…”

“…Signatures of MBS have been reported as a zero-bias conductance peak in tunnelling experiments [1][2][3][4][5]16 . The 4π Majorana-Josephson effect has been predicted and observed in nanowire Josephson junctions tuned to the topologically non-trivial regime 6,9 .…”

Phase-tunable second-order topological superconductor

“…From an experimental point of view, our model offers several advantages. First, it only requires conventional, s-wave superconductors, as well as the fabrication techniques recently developed in the context of Majorana nanowires, [72][73][74][75] including the deposition of a superconductor on a nanowire using in situ methods. Second, it allows for a topological phase to be reached for a range of phase differences, without the latter having to be set to a particular value.…”