Yu-Shiba-Rusinov-Bond Qubit in a Double Quantum Dot with Circuit-QED Operation

Abstract

Connecting two half-filled quantum dots to two superconducting leads induces a competition of bonds, with the dots forming either an interdot exchange bond or two individual Yu-Shiba-Rusinov (YSR) screening bonds with the leads. Defining a qubit using these singlet-parity bonding states provides dot-charge-noise protection, attributed to the chargeless nature of the screening quasiparticles, and magnetic noise protection, as the bonds guard against magnetic polarization. In this paper, we propose embedding a double-quantum-dot (DQD) Josephson junction in parallel with a transmon to enable circuit-quantum-electrodynamics (cQED) measurements and operation of a YSR-bond qubit. We demonstrate that, under realistic parameters, two-tone spectroscopy of the DQD can be performed, revealing a significant parameter regime suitable for qubit operation. Additionally, coherent manipulations of the bond states can be achieved through dot gates and single-shot readout is enabled by measurements of a capacitively coupled resonator. Finally, we analyze noise sources and estimate gate noise on couplings as the primary source of qubit decoherence. Since this qubit is protected against nuclear Overhauser fields and does not rely on spin-orbit interactions for operation, a broader range of material platforms becomes available compared to current Andreev spin qubits.