Work performed during the project is organised into five strongly linked research work packages (WPs) and two administrative WPs. The first four WPs focus on developing a toolkit for quantum light pulses: Sources (WP1), Manipulation (WP2), Detection (WP3), and Underpinning Theory (WP4). This toolkit is utilised in WP5 Applications to demonstrate three key quantum information tasks.
WP1 Sources: Approaches to generating trains of ultrafast pulses with a variety of quantum states optimised for the target applications have been developed. These differ in wavelength and pulse durations, but all approaches are based upon nonlinear optical techniques. Main results include generation of narrow-bandwidth photon pairs for quantum memories, a telecommunications wavelength photon pair source with tuneable spectral-temporal entanglement, and squeezed light sources of targeted pulsed modes.
WP2 Manipulation: Techniques based upon dynamic phase modulation with electro-optic modulators, nonlinear optics, and quantum memories to coherently manipulate quantum light pulses have been developed. Key results include the demonstration of quantum-pulse-gating of single-photon and squeezed states of light, single-photon pulse-mode shaping by application of well-controlled dynamic phase, and demonstration of quantum-memory based temporal-mode manipulation.
WP3 Detection: Two general approaches to implement quantum pulse detectors have been developed in the project. The first method relies on interfering the quantum optical state of light with a known reference field and examining the interference pattern as the reference is scanned. The second method involves manipulation of the unknown pulse using either the quantum pulse gate or direct temporal phase modulation to perform known operations followed by direct detection. Key results are the capability to characterise squeezing in multimode quantum light, single- and two-photon pulse-mode state reconstruction.
WP4 Underpinning Theory: Work has established foundational theory to describe the state and measurement of complex quantum pulses containing more than one photon. Key results include developing methods to analyse non-classical properties of quantum systems such as entanglement, which is essential to the performance enhancement for quantum technologies. Theoretical methods for quantum-enhanced precision metrology and means to manipulate the quantum state of pulse modes of light by measurement induced back action have been developed. The analysis of different time lenses for quantum imaging has been performed.
WP5 Applications: To demonstrate the technical advances enabled by the quantum pulse toolkit, applications in three areas of quantum technologies have been demonstrated: quantum computation - entanglement distillation on pulsed modes and proof-of-principle operations on multimode pulsed entangled states for cluster-state quantum computation have been realised; quantum communications - the ability to perform quantum key distribution based upon time-frequency encoding has been established experimentally; quantum sensing - capability of quantum light pulses to enhance multi-parameter estimation has been shown.
WP6 Administration: Efforts have involved organisation of six consortium meetings, where continued monitoring of progress and feedback on potential risks took place. Work also involved establishing shared platforms for collaboration, production of technical and financial reports, assisting with technical management issues, communication with project officer, and maintaining project website.
WP7 Dissemination and Impact: Scientific dissemination involved over 80 publications of research results in scientific journals, numerous presentations at international conferences and invited seminars, and organisation of an international summer-school and conference. Broader dissemination activities include creation of project logo, website, and two explainer videos, as well as participation in a range of outreach activities. Exploitation of results from the project include three patents filed, new collaborations with industry, and a number of PhD students from the project moving to related industrial positions.
