Photonic integration of 2D materials for room temperature single photon generation

Modern society is built upon our ability to communicate sensitive information securely, which is protected through cryptographic methods that rely on the inability of even the most powerful supercomputers to solve certain mathematical problems. However, with the advent of quantum computing it is only a matter of time before this security is breached. It is fortunate that quantum technology can also guarantee secure communication, where Quantum Key Distribution (QKD) employs the fragile nature of quantum states to detect any breach of security. QKD is a mature technology with commercial systems currently reaching the market for the most critical of applications, such as national security and high value financial transactions. With the ever-increasing reliance on mobile technology and the growing threat to conventional cryptography it is vital that solutions compatible with handheld devices are developed. This is currently limited by the availability of suitable single photon sources, which we aim to address in this project through the development of chip integrated quantum light sources built from two-dimensional (2D) materials.

So called 2D materials, those with a thickness of just a few atomic monolayers, have great potential in this area. The first to be discovered was graphene, an isolated single layer of carbon atoms, first produced in a laboratory in 2004. Remarkably, the first graphene samples were isolated using sticky tape to peel away atomic layers from graphite, which is not dissimilar to the "lead" found in ordinary pencils. As a result, graphene samples can be produced easily and cheaply, allowing scientists to make rapid progress in the understanding of physical processes and unlock the potential for applications. This success with graphene has inspired scientists to look for other atomically thin materials, with considerable success and an ever-expanding list of stable 2D crystals. Unlike graphene, several of these emit visible light making them great contenders for next-generation optoelectronic devices. Very recently, with the discovery of single photon emitters reported in monolayers of transition metal dichalcogenides and boron nitride, this potential has been expanded to quantum photonic applications. In particular, atomic-scale defects in boron nitride have been shown to emit single photons at room temperature, which puts 2D materials amongst a very small number of room temperature quantum emitters. Early experiments indicate that high brightness and stable emission could mean boron nitride is unmatched as a system for room temperature quantum photonics.

In this work we seek to take full advantage of this potential and will investigate the physical processes and atomic structure underpinning the quantum emission, methods of fabrication and photonic control of the emission. Ultimately, the aim will be to realise a platform consisting of defect emitters coupled to photonic circuits. Photonic integrated circuits enable the control and manipulation of light at the chip-scale and can benefit from the same economies of scale that have driven the microelectronics industry; namely that lithographic techniques can be employed to compress a large number of components into a very small volume to realise complex and efficient functionality. Development of integrated photonics is being driven by the huge power demands of data centres, which are increasingly using optical interconnects and the direct integration of photonics with CMOS electronics. Such photonic integrated circuits are important for the inclusion of quantum photonic devices within mobile devices because of the obvious size and weight constraints. The goal of this project will be to bring together quantum emitters in 2D materials with integrated photonics to provide a room temperature and portable solution for quantum secure communication.

This project can make a significant contribution to the delivery of economic and social benefits. Society is increasingly dependent on communications infrastructure and mobile computing devices. As a result huge quantities of sensitive data, including financial and personal information, are communicated on a daily basis and it is imperative that this data is kept secure. Quantum technology provides the means to guarantee this security, and this project will make a direct contribution to enabling the protection of data transmitted by mobile devices. The importance of secure communication also assures the economic benefits of this research; Quantum technologies in general provide a huge opportunity for wealth generation, with excellent potential for high-value manufacturing and new spin-out companies. One example of the potential value of quantum secure communication for mobile technology is in secure ATM transactions, a market with a predicted worth of £100m per year. The development of chip integrated and efficient quantum light sources, is fundamental to such systems and this research has real potential to make a significant impact in this area. A strong interaction with the EPSRC Quantum Communications Hub and the University of Bristol will provide a great opportunity to promote our work to quantum technology communities in the UK and to explore industry partnerships. This link will also enable the assessment of our devices in a quantum key distribution test-bed and form a partnership for securing future resources.

To realise the bright future of quantum technology, for applications and wealth generation for the nation, also requires highly trained scientists and engineers. This project provides a superb opportunity for the early career researchers involved to experience a cross-disciplinary project, gain first-hand experience of quantum photonic engineering and interact with European and industrial collaborators. Quantum technologies provide a huge opportunity for UK science and technology and it is imperative that students receive training in this area. The scientific advances in semiconductor physics, quantum optics and integrated photonic devices that will arise from this project will provide a strong training opportunity for the junior researchers and students involved. The project will provide inspiration to undergraduate students through the PI's teaching of Communications Engineering, which will be updated to include quantum communications, with a direct link to this project and will serve as an introduction to the vast opportunities quantum technologies provide for the future of science and engineering.