Fabrication and characterization of flux-tunable qubits in an InAs-Al 2DEG system

Proximitized two-dimensional electron gas (2DEG) in a hybrid superconduting-semiconducting system serves as an alternative approach for quantum computing due to its scalability and electrical gate tunability [1]. Typical gatemon qubits using hybrid superconductor-semiconductor Josephson junctions (JJs) [2] enable electrical gate tunability of the junction Josephson energy E_J , but limits the qubit’s performance due to dielectric loss [3]. Here, we present continuous-wave measurements on a split Cooper pair box qubit in an epitaxial Al-InAs 2DEG system. We find that the qubit frequency can be tuned with magnetic flux, resulting in a flux-tunable E_J/E_C ratio of 11 at the sweet spot. In addition, time-domain measurements are performed to determine various loss mechanisms in such hybrid 2DEG circuits for enhancing the qubit coherence times.

[1] N. Pankratov et al., Phys. Rev. X 10, 031051 (2020)

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

[3] W. M. Strickland et al., arxiv:2309.17273