Active Multiplexing of Spectrally Engineered Heralded Single Photons in an Integrated Fibre Architecture

Abstract

In recent years, there has been rapid development in processing of quantum information using quantum states of light. The focus is now turning towards developing real-world implementations of technologies such as all-optical quantum computing and cryptography. The ability to consistently create and control the required single photon states of light is crucial for successful operation. Therefore, high performance single photon sources are very much in demand.The most common approach of generating the required nonclassical states of light is through spontaneous photon pair generation in a nonlinear medium. One photon in the pair is detected to "herald" the presence of the remaining single photon. For many applications the photons are required to be in pure indistinguishable states. However, photon pairs generated in this manner typically suffer from spectral correlations, which can lead to the production of mixed, distinguishable states. Additionally, these sources are probabilistic in nature, which fundamentally limits the number of photons that can be delivered simultaneously by independent sources and hence the scalability of these future technologies.One route to deterministic operation is by actively multiplexing several independent sources together to increase the probability of delivering a single photon from the system. This thesis presents the development and analysis of a multiplexing scheme of heralded single photons in high-purity indistinguishable states within an integrated optical fibre system. The spectral correlations present between the two photons in the pair were minimised by spectrally engineering each photonic crystal fibre source. A novel, in-fibre, broadband filtering scheme was implemented using photonic bandgap fibres. In total, two sources were multiplexed using a fast optical switch, yielding an 86% increase in the heralded count rate from the system. AcknowledgementsI would first like to express my gratitude to my supervisor Dr. Peter Mosley, for giving me the opportunity to work with him on an exciting and interesting project, and for first introducing me to the world of quantum optics in the final year of my undergraduate degree. Without his support and guidance over the last three years, this thesis and the work that it contains would not have been possible. It has been a tremendously enjoyable learning experience (for both of us I hope!), and I think I can safely say that I now know more about FPGAs than I ever thought or hoped I would! I am incredibly grateful for the opportunity, and eagerly look forward to continue working with you on the upcoming NQIT project.Secondly, I would like to thank all of the staff and students, past and present, of the Centre for Photonics and Photonic Materials for providing an enjoyable, interesting and supportive learning environment. I would particularly like to thank James, for casting his eye over my fibre designs, passing down his fabrication knowledge, and teaching me the dark art of the dispersion rig! I would also especially like to ...

Multiplexing heralded single photons in orbital-angular-momentum space

“…For a multiplexed HSPS, an essential resource is entangled photon pairs emitted from nonlinear materials, for instance, processes of spontaneous parametric downconversion (SPDC) and spontaneous four-wave mixing. Many multiplexed HSPSs with high indistinguishability have been demonstrated in various DOF of photon [14], such as in spatial [15][16][17], temporal [18,19], polarization [20], spectral [21,22], and in both spatial and temporal [23,24]. For the spatial multiplexing HSPS, the strategy is to multiplex photon pairs in different spatial paths into a single path with the help of the optical switch, where one used to employ multiple basic units to generate photon pairs, i.e., arrayed silicon waveguides [15], bulk crystals [12] and fibres [16].…”