SAW-driven single-photon sources and photon detectors fabricated on an undoped GaAs/AlGaAs quantum well

Over the last few decades there has been strong interest in quantum information systems based on photonic qubits. Devices able to emit pure single-photon states on demand and detect incoming single photons in the system are fundamental building blocks for the realisation of a quantum photonic scheme. Advances in controlling single carriers have made it possible to transport single electrons using surface acoustic waves (SAWs). In a lateral n-i-p junction SAW-driven single-electron transport can be exploited to pump single electrons across the junction and generate single photons. In this work, devices have been developed in which both electrons and holes can be induced in an undoped GaAs/AlGaAs 15nm quantum well by gates to form a lateral n-i-p junction. The junction is confined into a quasi-1D channel laterally by etching and side gates. Light emission is observed when a 1 or 3 GHz SAW drives a current, by pumping electrons over the potential hill in the intrinsic region. SAW-driven electroluminescence has been characterised in the regime where less than one electron is transported per cycle on average. Time-resolved electroluminescence has been used to extract the electron recombination time and to quantify the contributions from electromagnetic crosstalk and the SAW. In a device without significant crosstalk, the degree of second-order coherence, g(2)(0) , shows the signature of antibunching. Hole SAW-pumping has been investigated as an alternative to electron pumping, showing a shorter recombination time. The dynamics has been further investigated with time-resolved and energy measurements at the junction, using a sub-micron positioner with lens assembly to scan along the pumping direction. A key requirement for practical quantum devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Using the same type of heterostructure, photons are detected by collecting and measuring the photo-generated carriers. An external light source sends photons into the system, and when they are absorbed in the quantum well, they create electron-hole pairs. The photo-generated carriers are separated and transported by a SAW together with an electric field applied by gates on the surface. The carriers are then collected by ohmic contacts, in order to extract information about the number of photons absorbed. Using the same 15nm GaAs/AlGaAs quantum well as for the single- photon source, an acousto-electric photon detector has been realised and characterised. Single-photon sensitivity can be achieved by measuring the photo-generated charges at single-particle level. The possibility to include single-electron and single-hole charge readout using quantum dots and quantum point contacts has been investigated.