QuICHE: Quantum information and communication with high-dimensional encoding

High-dimensional (HD) photonic quantum information (QI) promises considerable advantages compared to the two-dimensional qubit paradigm, from increased quantum communication rates to increased robustness for entanglement distribution. This project aims to unlock the potential of HD QI by encoding information in the spectral-temporal (ST) degrees of freedom of light. We will develop matched experimental tools and theoretical architectures for manipulating and characterizing such states, and we will demonstrate their use in applications. Every light beam has a large capacity for information coding in its ST degrees of freedom, which, through broadband optical fiber communications, underpins the massive capacity of the internet. Quantum light beams inherit this capacity, which has been as-of-yet underexplored and underutilized. ST control of quantum states of light enables multiplexing of QI in a single spatial mode, ideally suited for guided-wave communications and integrated devices. QI encoding in HD states, going well beyond two-dimensional encoding, has been recognized as a promising way towards enhanced QI processing, communication, and sensing. Even with an increasing number of theoretical proposals, there are, however, few experimental demonstrations of this capability. What is needed is a unified theoretical approach to HD quantum states that is relevant to real experimental devices, accounting for real-world imperfections in order to unlock the full potential of ST-encoded HD QI processing. This project will deliver such a joint effort to bridge this gap. We will carry out connected theoretical and experimental research to achieve secure communication in bipartite and multipartite scenarios, enhance the performance of quantum networks, and develop efficient methods for dimension witnesses, entanglement certification, estimation of properties of quantum states and channels, and quantum metrology. Moreover, we will introduce and develop the new concept of HD quantum temporal imaging. Experimental implementation will be based on novel HD encodings in time and frequency based on ultrafast quantum optical approaches in nonlinear waveguide and electro-optic devices. Encodings using broadband field-orthogonal overlapping pulse modes as well as distinct, non-overlapping time and frequency bins will be explored and brought together to form an effective hybrid-encoded network. Key to experimentally accessing the HD potential of the ST encoding will be the noiseless manipulation of time scales using the concepts of quantum temporal imaging. Combined experimental and theoretical efforts will yield a unified platform for HD, integrated optical QI processing, communication, and sensing.

With QuICHE, we propose an ambitious research programme that will lay the foundations for novel, high-dimensional quantum technologies; hence we anticipate a significant impact on science, industry, and society. The interplay between theory and experiment will allow us to deliver targeted demonstrations of key technologies with immediate relevance to real-world applications. HD encodings in multi-partite quantum networks promise increased information capacity and robustness against environmental decoherence. In the following, we will detail the contributions of QuICHE to the target impacts identified in the Call Announcement.