Nanotube spin defects for omnidirectional magnetic field sensing

TL;DR

This paper reports the discovery of spin defects in boron nitride nanotubes that enable orientation-independent magnetic sensing and demonstrate potential for atomic-scale quantum magnetometry.

Contribution

It introduces room-temperature single spin defects in BNNTs with unique orientation-independent sensing capabilities, advancing nanoscale quantum sensing technology.

Findings

Observation of single spin color centers in BNNTs at room temperature

Spin defects have a spin $S=1/2$ ground state without a fixed quantization axis

Demonstrated anisotropic magnetization detection of a 2D magnet

Abstract

Optically addressable spin defects in three-dimensional (3D) crystals and two-dimensional (2D) van der Waals (vdW) materials are revolutionizing nanoscale quantum sensing. Spin defects in one-dimensional (1D) vdW nanotubes will provide unique opportunities due to their small sizes in two dimensions and absence of dangling bonds on side walls. However, optically detected magnetic resonance of localized spin defects in a nanotube has not been observed. Here, we report the observation of single spin color centers in boron nitride nanotubes (BNNTs) at room temperature. Our findings suggest that these BNNT spin defects possess a spin $S=1/2$ ground state without an intrinsic quantization axis, leading to orientation-independent magnetic field sensing. We harness this unique feature to observe anisotropic magnetization of a 2D magnet in magnetic fields along orthogonal directions, a challenge for conventional spin $S=1$ defects such as diamond nitrogen-vacancy centers. Additionally, we develop a method to deterministically transfer a BNNT onto a cantilever and use it to demonstrate scanning probe magnetometry. Further refinement of our approach will enable atomic scale quantum sensing of magnetic fields in any direction.