To date quantum key distribution (QKD) has been the prime example of experimental quantum information. QKD permits two authorised parties to generate a cryptographic key with a level of security verified by quantum mechanics, as opposed to the computational difficulty of inverting certain mathematical functions. An unauthorised eavesdropper intercepting the single‑photon element of the key generation process will perturb the quantum states of the single photons to an extent which can be quantified by the authorised parties. We have a track record in researching ground breaking QKD systems: for example, work in the field led to the first demonstration of a quantum key distribution system operating at a clock‑rate of a gigahertz (and above) over an optical fibre link and the development of a novel environmentally robust test‑bed capable of long‑term autonomous operation.
These skills have now been applied to a new approach to a different data security issue, digital signatures, which are needed to sign and authenticate a message. The group developed the world's first experimental demonstration of quantum digital signatures, where the security of the exchange and authentication of the signatures is guaranteed by the fundamental laws of quantum mechanics. Crucially, this system enables the transmission of the same signature from one sender to two receivers and the verification between those two receivers that they have received identical signatures. This is fundamentally different to QKD, which only allows the creation of a shared cryptographic key between one sender and a single receiver (even in a multi‑recipient system).
Over the years this system has been developed until it now operates over kilometre ranges in standard telecommunications optical fibre using hardware similar to that of QKD. This offers the prospect of commercial deployment of this technology in quantum secure networks.
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Quantum Digital Signatures
R.J. Donaldson, R.J. Collins, K. Kleczkowska, R. Amiri, P. Wallden, V. Dunjko, J. Jeffers, E. Andersson, and G.S. Buller, "Experimental demonstration of kilometer‑range quantum digital signatures", Physical Review A 93(1), Article Number 012329 (2016).
R.J. Collins, R.J. Donaldson, V. Dunjko, P. Wallden, E. Andersson, J. Jeffers, and G.S. Buller, "Realization of Quantum Digital Signatures without the requirement of quantum memory", Physical Review Letters 113, Article Number: 040502 (2014).
P.J. Clarke, R.J. Collins, V. Dunjko, E. Andersson, J. Jeffers and G.S. Buller, "Experimental demonstration of quantum digital signatures using phase‑encoded coherent states of light", Nature Communications, 3 Article number: 1174 (2012)
The Journal, "Light-fingered physicists in e‑crime breakthrough"