Quantum Photonics

Jean-Luc Tambasco

This thesis investigates quantum photonic technology, proposing novel designs and photonic components towards the next generation of quantum computing and information processing. Chapter 1 introduces the history and motivation behind quantum information, and evaluates today’s most promising quantum technology platforms. Chapter 2 provides an overview of requisite linear and nonlinear classical photonic theory, introduces topological photonics and quantum photonic concepts, as well as nanofabrication principles. In chapter 3, a published novel probabilistic single photon source design is proposed, aimed at improving yield and photon purity. Chapter 4 proposes a published novel scheme for manipulating photons with the goal of enabling robust new quantum photonic gate designs. Chapter 5 introduces two works investigating a new photonic platform, lithium niobate on insulator (section 5.1), suitable for quantum photonic technology, and demonstrates the initial steps towards the development of spectral filtering on this platform (section 5.2). This thesis seeks to explore and advance future quantum photonic technology, from sources design to quantum photonic gate design and fabrication, stepping closer to the long standing dream of scalable photonic quantum computing.

Thomas P. Pearsall

Liang Zhai, Giang N. Nguyen, Clemens Spinnler +6 more

Photonic quantum technology provides a viable route to quantum communication, quantum simulation, and quantum information processing. Recent progress has seen the realisation of boson sampling using 20 single-photons and quantum key distribution over hundreds of kilometres. Scaling the complexity requires photonic architectures containing a large number of single photons, multiple photon-sources and photon-counters. Semiconductor quantum dots are bright and fast sources of coherent single-photons. For applications, a significant roadblock is the poor quantum coherence upon interfering single photons created by independent quantum dots. Here, we demonstrate two-photon interference with near-unity visibility using photons from remote quantum dots. Exploiting the quantum interference, we demonstrate a photonic controlled-not circuit and a high-fidelity entanglement between photons of different origins. Our results provide a long-awaited solution to the challenge of creating coherent single-photons in a scalable way. In the near future, they point to a demonstration of quantum advantage using quantum-dot single photons and an implementation of device-independent quantum key distribution.

Thomas P. Pearsall

Matthew Bradford

The field of quantum nanophotonics has recently been attracting a great deal of interest. In quantum nanophotonics, fermionic degrees of freedom such as atoms or quantum dots are coupled to traditional nanophotonic systems. As the fermionic components can only absorb a finite number of photons at a time, the interplay between the fermionic and photonic degrees of freedom can fundamentally alter the transport properties of photons and their correlations. In many conventional photonic systems, however, atom-photon interactions are too weak to realize efficient devices at ultra-low power levels. We show that in properly designed quantum nanophotonic geometries, we can create strong photon-photon interaction and quantum interference to realize efficient devices operating down to the single-photon power level. In particular, quantum nanophotonic geometry allows us to establish quantum interference to provide efficient single-photon frequency conversion and long-term photonic storage. Moreover, we use strong photon-photon interactions in cavity-QED to produce strongly antibunched streams of photons with shot noise below the classical limit which can allow fundamentally secret communication over large distances.