Efficient spin-photon interfaces for distributing entanglement

Abstract

At last, use for quantum entanglement is on the horizon. Large computer companies race to build small quantum computers, usually based on superconducting circuits. The most elusive but rewarding of quantum-enabled technologies, however, would be the spin-photon interface for distributing entanglement. Elusive because single atoms are hard to isolate, and put into scalable systems. Rewarding because distributing entanglement over networks, using modular nodes, would result in quantum information resources that scale exponentially with the number of connected nodes. This in-built complexity would be unrivalled once proven. To do this, viable spin-photon interfaces will require harnessing established semiconductor technologies – integrating nanophotonics to filter and manipulate light and integrating nanoelectronics to provide the control of atom-like spins and classical processing of information.
The Nitrogen Vacancy (NV) centre in diamond is perhaps the best understood optically-accessible atom-like system in a semiconductor and has been demonstrated as a spin-photon interface by entangling separate NV centres over a kilometre photonic channel. In this thesis, I borrow computational techniques to rapidly find and characterise NV centres with applications for large scale integration. For the first time, I evidence successful incorporation with a silicon-compatible platform, by encapsulating NV centres in nitrogen-rich silicon nitride by which the atom-like emitter would strongly couple to the centre of the silicon nitride waveguide mode. I measure the quantum signatures of single photon anti-bunching and electron spin Rabi oscillations of the same NV centre before and after deposition of 100 nm of PECVD nitride. Following this, I iterate to a mature out-coupler through planar lithography towards a scalable free space atom-photon interface in this platform. Finally, I consider how spin-photon interfaces could be improved, even above liquid-helium temperatures, and develop a novel planar cavity that will produce indistinguishable photons at Peltier-cooled temperatures, a further economic necessity for distributing entanglement over large networks.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	John G Rarity (Supervisor) & Krishna Coimbatore Balram (Supervisor)