Gateless Gatemon Qubit in a Two-dimensional InAs-Al heterostructure

Gatemon qubits represent an all-electric variant to the conventional transmon, where local electrically gated superconductor-semiconductor hybrid Josephson junctions (JJs) [1] are employed for qubit operations. Here we demonstrate the operation of split-junction gatemons biased at the half-integer flux quantum [2], which do not require any electrical gating at all. Such “gateless gatemon" qubits naturally acquire a strong anharmonicity, as large as 2400%, while remaining first-order insensitive to flux noise. The observed rich transition spectra can be explained by the interference of supercurrents carried by highly transparent Andreev bound states (ABSs) with 2e, 4e and higher even multiples of charges across the junctions. Another useful property of the half-integer flux bias operation is a partial suppression of the transition matrix element responsible for the dielectric energy relaxation. Our result demonstrates feasibility of strongly anharmonic super-semi qubits. The bare minimum design of gateless gatemons combined with their broad frequency tuning range provide an efficient mechanism for comparing various super-semi materials platforms and implementing novel partially-protected qubits.



[1] L. Casparis et al., Nature Nanotechnology 13, 915-919 (2018)

[2] A. Bordoloi et al., “Gateless gatemon qubit based on two-dimensional InAs/Al heterostructure”, in preparation