Single-Nv-Center Quantum Memory for a Superconducting Flux Qubit Mediated by a Ferromagnet
Yen-Yu Lai1,2*, Guin-Dar Lin1,2, Jason Twamley3, Hsi-Sheng Goan1,2
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Center for Quantum Science and Engineering, National Taiwan University, Taipei, Taiwan
3Centre for Engineered Quantum Systems, Macquarie University, NSW, Australia
* Presenter:Yen-Yu Lai,
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 engaged in the state transfer process can enhance the effective FQ-NV-center coupling strength to MHz level without introducing additionally 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 spontaneous decay and pure dephasing effect. Using the realistic experimental parameters for the FQ, NV center and YIG, we find that a long storage time of 10 ms with combined transfer, storage and retrieval fidelity higher than 0.9 can be achieved. This hybrid system not only acts as a promising quantum memory architecture, but also provide an example of enhanced coupling between various systems through collective degrees of freedom.

Keywords: quantum memory, superconducting flux qubit, nitrogen-vacancy center (NV), yttrium iron garnet (YIG), magnon