Semiconductor Nanowire-based Quantum Light Sources for Quantum Networks

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The quantum network, whether as a platform to transfer information securely or to share quantum information amongst isolated few-qubit quantum computers, is becoming a reality. To build such a network will require quantum light sources operating at wavelengths where fibre losses are minimum (1310 and 1550nm). In order to achieve sufficient transmission rates, the quantum light sources will need to produce single photons and entangled photon pairs with near-unity efficiency. At present, sources are probabilistic (non-linear crystals or attenuated lasers) which limit efficiencies to ~1%. This program of research proposes to develop on-chip quantum light sources that combine the excellent optical properties of III-V nanowire quantum dots (NW QDs) with the low propagation losses of silicon-based photonics. The long term goal is to provide a scalable solution to generating quantum light with near unity efficiency and available at high repetition rates. Importantly, these photons will be generated at telecom wavelengths compatible with long-haul telecommunication fibres. The availability of such sources will greatly facilitate their implementation in secure quantum networks, where proof of principle has already been demonstrated and a drive for higher key transfer rates is foreseeable. We have an established process whereby individual NW QDs are grown at pre-selected positions on the growth substrate. Importantly, the NW geometry lends itself to a “pick and place” approach for on-chip integration, essentially allowing for the physical manipulation of single quantum emitters. On-chip integration will be achieved by picking up individual NWs from the growth substrate and placing them at specific locations on a substrate prepared with the appropriate photonic circuitry. The research program will start with optimizing source efficiency for devices operating at wavelengths of ~900nm using a SiN on-chip platform (PhD #1). Photonic structures (wavequides, resonators) will be designed for optimal coupling and spontaneous emission rates. The next stage of the project will develope NW sources at telecom wavelengths of 1310nm and 1550nm (PhD#2). These sources will be integrated on-chip using a silicon-on-insulator (SOI) platform. The know-how gained in SiN photonic circuits will be applied to Si to produce telecom wavelength sources operating at GHz emission rates (PhD #1&2). In parallel, a theoretical understanding of the quantum optical properties of NW QDs and their interactions with the environment will be developed (PDF#1). The last stage of the project will explore geometries and growth conditions whereby the III-V NWs can be grown directly on Si with a growth direction parallel to the substrate (PhD #3). If successful, this growth mode can be applied to pre-fabricated SOI photonic circuits to grow telecom wavelength single QDs at pre-selected positions, a truly scalable on-chip platform.