Spin emitters beyond the point dipole approximation in nanomagnonic cavities

TL;DR

This paper introduces a method to control spin transitions in emitters by placing them in nanomagnonic cavities, accounting for beyond point dipole effects, enabling new quantum information processing techniques.

Contribution

It develops a theoretical framework for driving forbidden spin transitions using nanomagnonic cavities with large field gradients, specifically applied to SiV$^-$ defects in diamond.

Findings

Calculated coupling rates of spin transitions to nanomagnonic modes.

Demonstrated the importance of beyond point dipole modeling.

Proposed applications in quantum state transduction.

Abstract

Control over transition rates between spin states of emitters is crucial in a wide variety of fields ranging from quantum information science to the nanochemistry of free radicals. We present an approach to drive a both electric and magnetic dipole-forbidden transition of a spin emitter by placing it in a nanomagnonic cavity, requiring a description of both the spin emitter beyond the point dipole approximation and the vacuum magnetic fields of the nanomagnonic cavity with a large spatial gradient over the volume of the spin emitter. We specifically study the SiV$^-$ defect in diamond, whose Zeeman-split ground states comprise a logical qubit for solid-state quantum information processing, coupled to a magnetic nanoparticle serving as a model nanomagnonic cavity capable of concentrating microwave magnetic fields into deeply subwavelength volumes. Through first principles modeling of the SiV$^-$ spin orbitals, we calculate the spin transition densities of magnetic dipole-allowed and -forbidden transitions and calculate their coupling rates to various multipolar modes of the nanomagnonic cavity. We envision using such a framework for quantum state transduction and state preparation of spin qubits at GHz frequency scales.