Single-Nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet

TL;DR

This paper proposes a hybrid quantum memory system using a superconducting flux qubit, a ferromagnet, and a nitrogen-vacancy center in diamond, achieving high fidelity and long storage times by leveraging collective spin modes.

Contribution

It introduces a novel scheme for quantum memory transfer and storage utilizing a ferromagnet to enhance coupling between a flux qubit and NV center.

Findings

Achieves transfer, storage, and retrieval fidelity above 0.9.

Demonstrates a long storage time of 10 milliseconds.

Shows the effectiveness of collective spin modes in enhancing coupling.

Abstract

We propose a quantum memory scheme to transfer and store the quantum state of a superconducting flux qubit (FQ) into the electron spin of a single nitrogen-vacancy (NV) center in diamond via yttrium iron garnet (YIG), a ferromagnet. Unlike an ensemble of NV centers, the YIG moderator can enhance the effective FQ-NV-center coupling strength without introducing additional appreciable decoherence. We derive the effective interaction between the FQ and the NV center by tracing out the degrees of freedom of the collective mode of the YIG spins. We demonstrate the transfer, storage, and retrieval procedures, taking into account the effects of spontaneous decay and pure dephasing. Using realistic experimental parameters for the FQ, NV center and YIG, we find that a combined transfer, storage, and retrieval fidelity higher than 0.9, with a long storage time of 10 ms, can be achieved. This hybrid system not only acts as a promising quantum memory, but also provides an example of enhanced coupling between various systems through collective degrees of freedom.