Coherent control of spinmons

TL;DR

This paper proposes a new qubit encoding called spinmons, entangling transmon states with trapped quasiparticle spins, to improve noise robustness in superconducting qubits.

Contribution

It introduces the concept of spinmons, demonstrates methods for full control via gates and flux drive, and analyzes their coherence properties.

Findings

Spinmons can be controlled electrostatically and with AC flux.

They exhibit robustness against flux and charge noise.

Theoretical coherence times are computed for spinmons.

Abstract

The protection of superconducting qubits from certain noise sources often comes at the cost of increased sensitivity to other decoherence channels. Here, we explore a route to avoid this tradeoff by encoding quantum information in quantum states of a transmon entangled with the spin of a trapped Andreev quasiparticle. We term such devices spinmons. We lift the spinmon Kramers degeneracy by introducing a Zeeman field and develop two routes for full qubit control via electrostatic gates and an AC flux drive, providing multiple directions for experimental implementations. Finally, we compute coherence times and verify the qubit robustness against flux and charge noise sources.