Together with quantum metrology, quantum cryptography and quantum key-distribution are the subfields of quantum-information processing that have delivered the most significant impact on realised technologies. The incompatibility of non-commuting observables’ in quantum mechanics led to the introduction of quantum-based cryptography protocols, which, in theory, are fundamentally uncrackable. With the immense improvements that have happened to single-photon detectors and emitters, early prototypes of these protocols are now available on the market.

A major obstacle in the industrial development of quantum cryptography technologies is the monetary cost of producing accurate/precise photon detectors. The QI group has generated ground-breaking research in the area of low-photon-number detectors. The work has resulted in publications and a patent. The technology is currently employed by the Cambridge-based spin-off company Nu Quantum.

Over the last few decades, quantum mechanics has been shown to break classical bounds on information theory. The QI group has, in a series of articles, studied a phenomenon known as counterfactual communication. The group has played a pivotal role in establishing the quantum-mechanical process of transmitting information without the transmission of physical particles. A highlight of the group’s work was the 2019 publication of the first-ever experimental demonstration of the transmission of a human-readable picture message without physical particles, with an error less than 1%. The publication was the product of a collaboration where the Cavendish QI group provided theory and guiding simulations, MIT constructed nanophotonic processors, and the University of Vienna conducted single-photon experiments.