Coherent manipulation of an Andreev spin qubit

TL;DR

This paper demonstrates coherent control of an Andreev spin qubit in a semiconductor-superconductor nanowire, combining advantages of spin and superconducting qubit platforms, with potential implications for quantum computing.

Contribution

It introduces the Andreev spin qubit, a novel hybrid qubit platform that integrates spin control with circuit-QED readout in semiconductor-superconductor systems.

Findings

Achieved spin-flip time of 17 microseconds

Measured spin coherence time of 52 nanoseconds

Demonstrated coherent manipulation of Andreev levels

Abstract

Two promising architectures for solid-state quantum information processing are electron spins in semiconductor quantum dots and the collective electromagnetic modes of superconducting circuits. In some aspects, these two platforms are dual to one another: superconducting qubits are more easily coupled but are relatively large among quantum devices $(\sim\mathrm{mm})$, while electrostatically-confined electron spins are spatially compact ($\sim \mathrm{\mu m}$) but more complex to link. Here we combine beneficial aspects of both platforms in the Andreev spin qubit: the spin degree of freedom of an electronic quasiparticle trapped in the supercurrent-carrying Andreev levels of a Josephson semiconductor nanowire. We demonstrate coherent spin manipulation by combining single-shot circuit-QED readout and spin-flipping Raman transitions, finding a spin-flip time $T_S = 17~\mathrm{\mu s}$ and a spin coherence time $T_{2E}=52~\mathrm{ns}$. These results herald a new spin qubit with supercurrent-based circuit-QED integration and further our understanding and control of Andreev levels -- the parent states of Majorana zero modes -- in semiconductor-superconductor heterostructures.