Quantum dots—tiny semiconductor crystals—are being engineered to emit single particles of light on demand, a key requirement for quantum computers and unhackable communications. Today’s best quantum dots work at 950 nanometres, a wavelength that does not match the fibre-optic networks or quantum memory systems already in place. This project tackles that mismatch by growing strain-free gallium arsenide quantum dots inside aluminium gallium arsenide membranes. The team will use a dedicated molecular beam epitaxy reactor to control layer thickness and doping with atomic precision, then integrate the dots into p-i-n diodes and nanobeam waveguides. They aim to produce the first voltage-controlled quantum dot molecules in this material system, creating a spin-photon interface that can generate entangled photon cluster states. If successful, the work would provide a monolithic platform that combines the nonlinear optical properties of the bulk semiconductor with the quantum properties of the dots. That could enable on-chip frequency conversion to telecom wavelengths, low-loss fibre transmission, and scalable production of entangled photons for secure communications, quantum sensing, and quantum computing. The project is primarily fundamental materials science, but it directly addresses a bottleneck that currently prevents quantum light sources from connecting to existing infrastructure.
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Bright, efficient quantum light sources for the generation of single and entangled photon states are essential for transferring and processing quantum information in emerging quantum technologies. Quantum light sources based on individual III-V semiconductor quantum dots (QDs) operating at wavelengths around 950nm have key figures of merit that no other source can match. However, significant materials challenges remain for the development of scalable QD quantum light sources emitting at more technologically relevant wavelengths that overlap with established quantum memories and provide low loss fibre-based optical transmission. Here, we address this challenge through a materials-focussed programme that will provide a monolithic QD platform for future integration with quantum memories, efficient on-chip frequency conversion to telecoms wavelengths and on-demand generation of large entangled photonic ‘cluster’ states, with important application in secure communications, sensing and quantum computing. We will capitalise on the very favourable properties of strain-free GaAs QDs, developing growth approaches to enable efficient operation of QDs embedded in tightly-confining, single mode AlGaAs waveguides. Careful control of layer thicknesses and doping levels will be achieved during growth using a dedicated molecular beam epitaxy reactor, integrated with quantum optical spectroscopic characterisation and device fabrication in state-of-the-art facilities. Our research objectives are: Design and grow single GaAs QDs in AlGaAs membranes with world-leading optical properties by incorporating the QDs in p-i-n diodes. Design and grow the first GaAs QD molecules in AlGaAs p-i-n diode membranes, providing a high-performance, voltage-controlled spin-photon interface. Demonstrate on-chip single photon generation and routing using optimised GaAs QDs in AlGaAs nanobeam waveguides. A key benefit of our approach lies in the use of AlGaAs, which due its high optical nonlinearity and favourable materials properties is emerging as a leading choice for quantum photonic integrated circuits (QPICs). By incorporating single GaAs QDs via monolithic integration, our materials platform combines bulk (AlGaAs) and quantum (QD) nonlinearities, opening up new directions for future advanced QPIC operation. The project will establish a close collaboration between academic researchers with highly complementary expertise in QPICs (project lead, PL), QD quantum light sources and QD growth (project co-leads). Funding will also enable the PL to develop important new collaborative links with the National Epitaxy Facility and a leading spin-out company developing integrated photonics for quantum networking and computing.
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