Quantum Spin-Photon Entanglement in a Two-Dimensional Material

In 2023 we are on the verge of the ‘3rd quantum revolution’ where advances of the past century, across the theory of quantum mechanics, experimental physics and material science, will combine to deliver large-scale quantum technologies. This revolution will lead to breakthroughs across, for example, drug and materials discovery, environmental sensing, and cryptography. These breakthroughs are hoped to tackle the big challenges in healthcare, energy and security. A key technology will be optical quantum networks – a distribution of quantum states and entanglement between any two points on the globe. Such a network will be critical for linking independent quantum technologies, such as sensors and computers, as well as enabling ultimately secure communication. Realisation of a global quantum network requires materials to form ‘repeaters’, the network nodes that send and retrieve quantum information via photons and store it locally in a memory. Solid-state materials are a leading candidate because optically addressable electron and nuclear spins offer a spin-photon interface. However, so far, the few known solid-state systems require cryogenic operation, bulky architectures and/or difficult material processing, leading to challenges for scalability. Therefore, the hunt is on to find and develop the material platform with the spin and optical properties that can deliver a scalable quantum network. I propose to deliver a new platform for quantum networks based on a two-dimensional (2D) material. This system is comprised of single-photon emitting atomic-scale point defects in hexagonal Boron Nitride (hBN) that have an optically addressable quantum coherent spin-triplet ground state, providing a spin-photon interface. The hBN defect spin operates at ambient conditions (room temperature and in the absence of a magnetic field) and the defect shows highly favourable optical properties, indicating the 2D material platform has the potential to form the basis of multimode networks that could operate without cryogenic operation. This project will benchmark the system for quantum networks via the demonstration of spin-photon entanglement. To achieve entanglement, the project will develop the spin and optical properties of the hBN defects via quantum optical experiments as well as material and device processing. On the photon side, my team and collaborators will establish the fundamental optical model, including demonstrating optical coherence, and couple the defects to an optical cavity to enhance emission and demonstrate photon indistinguishability. For spin, controlled isotopic enrichment of the hBN material will be used to optimise the electronic spin coherence and demonstrate coherent control of strongly coupled nuclear spins, a resource for a long-lived quantum memory. The unique combination of a spin-rich nuclear lattice and an ultimately atomically thin material gives rise to new approaches, which I propose, to optimise the spin and optical properties in atomically thin devices. This proposal represents a paradigm shift in the approach to realising global quantum networks, via the development of a new platform in a 2D material with natural attributes for scalability. In doing so I believe this opens the door to exploring quantum phenomena in reduced dimensions with the potential that this system can be applied widely across quantum sensing and simulation, in addition to networking.