Fiber‐Integrated van der Waals Quantum Sensor with an Optimal Cavity Interface

Abstract Integrating quantum materials with fiber optics adds advanced functionalities to a variety of applications, and introduces fiber‐based quantum devices such as remote sensors capable of probing multiple physical parameters. However, achieving optimal integration between quantum materials and fibers is challenging, particularly due to difficulties in fabrication of quantum elements with suitable dimensions and an efficient photonic interface to a commercial optical fiber. Here a new modality for a fiber‐integrated van der Waals quantum sensor is demonstrated. A hole‐based circular Bragg grating cavity from hexagonal boron nitride (hBN) is designed and fabricated, engineer optically active spin defects within the cavity, and integrate the cavity with an optical fiber using a deterministic pattern transfer technique. The fiber‐integrated hBN cavity enables efficient excitation and collection of optical signals from spin defects in hBN, thereby enabling all‐fiber integrated quantum sensors. Moreover, remote sensing of a ferromagnetic material and of arbitrary magnetic fields is demonstrated. All in all, the hybrid fiber‐based quantum sensing platform may pave the way to a new generation of robust, remote, multi‐functional quantum sensors.