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Quantum Controlled Ultrafast Multimode Entanglement and Measurement

Periodic Reporting for period 2 - QCUMbER (Quantum Controlled Ultrafast Multimode Entanglement and Measurement)

Reporting period: 2016-09-01 to 2018-08-31

The QCUMbER project explores novel foundations for radically new future technologies based upon the quantum behavior of ultrashort light pulses. Optical pulses with duration of picoseconds (one trillionth of a second) or less have enabled the study and control of system dynamics, such as electronic motion within atoms and molecules, while highly stable trains of pulses have provided a platform for extremely precise measurements. Similarly, exploitation of the quantum behavior of light has enabled experimental probing of fundamental physics and led to the creation of the fields of quantum communication and sensing. The QCUMbER project aims to establish the foundational scientific underpinnings for ultrashort quantum light pulses and demonstrate essential proofs-of-principle applications for optical quantum technologies.

Quantum technologies is a rapidly growing area of research and innovation, with numerous applications such as physically-secure communications, increased computational capabilities, and high-precision, minimally-invasive sensing. These technologies are at the foundation of an emerging quantum technologies industry, which promises increased economic growth. In addition, the superior performance of quantum devices over those constructed using non-quantum principles will provide society with a broad range of advances and capabilities not currently feasible.

The primary goal of QCUMbER is to develop the resources needed to address the quantum structure of the time-frequency degree of freedom of ultrashort light pulses and to demonstrate their utility for new types of quantum technologies, such as communications, dynamical sensors and computation. The two primary research objectives for the project are

Objective 1: Toolkit for quantum light pulses - Develop a suite of tools enabling controlled generation, manipulation and measurement of quantum light pulses.

Objective 2: Proof of concept applications - Demonstrate the technological capabilities enabled by quantum light pulses by realising four targeted quantum applications.
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 i
The QCUMbER project has made significant progress beyond the state of the art in the essential building blocks for optical quantum technologies based upon pulsed modes. During the project, a toolkit for quantum pulses was developed, which provides methods to create, manipulate and detect highly multimode spectral-temporal quantum states of light and established the underpinning theory needed to describe ultrashort quantum light pulses. Utilising this toolkit, proof of concept experiments in quantum computation, communications and sensing were realised.

Utilising time-frequency quantum states of light offers a game changing approach to optical quantum technologies, opening new avenues for exploitation and making direct impact on European photonics industries. QCUMbER has established a new paradigm of pulse-mode quantum photonics by harnessing multimode time-frequency quantum states of light for quantum technologies that will alter future research directions. Indeed, the project results are being taken up by other research groups around the globe and are likely to initiate future innovations in the emerging field optical quantum technologies.
Artistic interpretation of an ultrafast quantum pulse, the central focus of the research in QCUMbER
Photograph of a photon-pair source in one of QCUMbER's experiments