Long-Range Interaction of Spin-Qubits via Ferromagnets

TL;DR

This paper proposes a method for coherently coupling distant spin qubits using ferromagnets, enabling fast entangling gates with minimal decoherence, especially applicable to atomistic spin-qubits like silicon-based and NV centers.

Contribution

It introduces a novel ferromagnet-mediated coupling mechanism for distant spin qubits, including an effective Hamiltonian and a practical entangling gate sequence.

Findings

Coupling strength estimated to be sufficient for fast gate operations.

Decoherence effects can be minimized in certain regimes.

Operation time for CNOT gate is estimated to be a few tens of nanoseconds.

Abstract

We propose a mechanism of coherent coupling between distant spin qubits interacting dipolarly with a ferromagnet. We derive an effective two-spin interaction Hamiltonian and estimate the coupling strength. We discuss the mechanisms of decoherence induced solely by the coupling to the ferromagnet and show that there is a regime where it is negligible. Finally, we present a sequence for the implementation of the entangling CNOT gate and estimate the corresponding operation time to be a few tens of nanoseconds. A particularly promising application of our proposal is to atomistic spin-qubits such as silicon-based qubits and NV-centers in diamond to which existing coupling schemes do not apply.