Quantum interface between a transmon qubit and spins of nitrogen-vacancy centers

TL;DR

This paper proposes a scheme to directly couple a transmon qubit with NV center spins, enabling efficient quantum state transfer, non-demolition measurements, and virtual coupling for hybrid quantum systems.

Contribution

It introduces a method for strong direct coupling between transmon qubits and NV centers, enhancing quantum information processing capabilities.

Findings

Coupling strength three orders of magnitude larger than previous methods

Feasibility of SWAP operation between transmon and NV ensemble

Enhanced virtual coupling enabling efficient photon state storage

Abstract

Hybrid quantum circuits combining advantages of each individual system have provided a promising platform for quantum information processing. Here we propose an experimental scheme to directly couple a transmon qubit to an individual spin in the nitrogen-vacancy (NV) center, with a coupling strength three orders of magnitude larger than that for a single spin coupled to a microwave cavity. This direct coupling between the transmon and the NV center could be utilized to make a transmon bus, leading to a coherently virtual exchange among different single spins. Furthermore, we demonstrate that, by coupling a transmon to a low-density NV ensemble, a SWAP operation between the transmon and NV ensemble is feasible and a quantum non-demolition measurement on the state of NV ensemble can be realized on the cavity-transmon-NV-ensemble hybrid system. Moreover, on this system, a virtual coupling can be achieved between the cavity and NV ensemble, which is much larger in magnitude than the direct coupling between the cavity and the NV ensemble. The photon state in cavity can be thus stored into NV spins more efficiently through this virtual coupling.