Control of an environmental spin defect beyond the coherence limit of a central spin

TL;DR

This paper demonstrates a scalable method to control and detect environmental spin defects beyond the coherence limit of a central NV spin, enabling larger quantum registers for sensing and communication.

Contribution

It introduces a weakly-coupled probe spin and double-resonance sequences to mediate spin transfer beyond direct coupling limits, expanding quantum register size.

Findings

Successful detection of an unknown environmental spin outside the NV coherence limit.

Experimental realization of polarization transfer via weakly-coupled probe spin.

Potential to engineer larger quantum spin registers for advanced quantum technologies.

Abstract

Electronic spin defects in the environment of an optically-active spin can be used to increase the size and hence the performance of solid-state quantum registers, especially for applications in quantum metrology and quantum communication. Previous works on multi-qubit electronic-spin registers in the environment of a Nitrogen-Vacancy (NV) center in diamond have only included spins directly coupled to the NV. As this direct coupling is limited by the central spin coherence time, it significantly restricts the register's maximum attainable size. To address this problem, we present a scalable approach to increase the size of electronic-spin registers. Our approach exploits a weakly-coupled probe spin together with double-resonance control sequences to mediate the transfer of spin polarization between the central NV spin and an environmental spin that is not directly coupled to it. We experimentally realize this approach to demonstrate the detection and coherent control of an unknown electronic spin outside the coherence limit of a central NV. Our work paves the way for engineering larger quantum spin registers with the potential to advance nanoscale sensing, enable correlated noise spectroscopy for error correction, and facilitate the realization of spin-chain quantum wires for quantum communication.