Multimode integrated time-frequency quantum photonics

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Quantum physics is at the centre of a technological revolution that promises to transform information and communications technologies (ICT) from secure communications, enhanced precision in measurement, high-capacity simulation and computation beyond that capable using only classical resources. These quantum-enhanced technologies will significantly increase the capacity to securely transmit and process the ever-rising volumes of data on which the global economy is based. The ability to simulate complex systems, both quantum and classical, could allow creation of new functional materials ranging from designer drugs to solar cells with improved efficiency. Furthermore, improved sensitivity in measurements opens paths to probe fundamental physics previously not accessible, as well as more practical applications such as low-light-level spectroscopy. Light will play a central role in many of these quantum technologies such as spectroscopy, imaging, communications, and computation. When addressing individual photons, information is most often encoded as one quantum bit (or qubit) of information per transmitted photon. However, this severely limits the information processing capacity of current approaches to small sizes. One recent approach to increase the complexity of quantum optical systems that can be achieved utilizes integrated quantum photonics, in which photons are generated, guided and manipulated on silicon chips. However, these techniques still rely on encoding information as qubits and do not take advantage of the rich structure of individual photons. This project will take a new approach to encoding an increased amount of information per photon, and thus allow significantly increased system complexity to be achieved.To increase the information capacity of single photons for integrated photonics this project will focus on encoding information in the time-frequency state of individual photons, in which the temporal shape and colour of the photon carry the information. This approach parallels methods used in classical ICT such as wavelength- and time-division multiplexing where information is encoded in the wavelength (colour) or arrival time of light pulses. This new approach is made possible by recent developments at Oxford in fibre-based photon sources and integrated quantum photonics, which allow deterministic frequency control of single photons. By moving to this regime of increased information capacity per photon on an integrated platform, the project aims to enable significant advances in quantum-enhanced technologies. Further afield the techniques for low-light-level time-frequency sensing developed during the project could be utilized in a diverse range of applications from spectroscopy to optical network diagnostics