Metrology for industrial quantum communication technologies

Quantum communication technologies such as quantum key distribution (QKD) can improve the security of the ever-increasing amount of sensitive information that is stored, transferred and accessed over computer networks. The unique feature of QKD is that, when implemented correctly, the system guarantees that the encryption key has not been intercepted. In theory, it is extremely effective but there are no agreed methods to demonstrate that practical implementations are robust. The main challenge is the identification of the physical system parameters critical to QKD and the development of appropriate metrics and measurement techniques for their quantification, in particular the properties of quantum sources, channels and receivers.

This project developed:

• Techniques for traceable characterisation of photon sources with unknown quantum states including methods for measuring the mean photon number at communications wavelengths traceable to the SI, a novel photon-number-resolving (PNR) detector capable of measuring more than one photon in a pulse, a high-resolution, high-transmission fibre-coupled single-photon spectrometer suitable for spectral analysis of pulsed sources at communications wavelengths and an optimised single-photon source as a reference for quantum sources.
• Tools for traceable characterisation of quantum channels for optical fibre-based communication systems including development of ‘open system’ quantum random number generators – an essential tool in encryption and the development of a single-photon polarimeter for reconstructing the polarisation state of a single photon transmitted down an optical fibre – used to measure system noise using conventional light levels transmitted via a standard communication fibre optic link.
• Methods for traceable characterisation of single-photon detectors including characterisation methods for determining parameters and properties of commercially-available single-photon detectors and a calibrated attenuator to simplify detector characterisation and determine quantum efficiency with an uncertainty of less than 3 %.

The project put in place a series of measurement systems that characterise the properties of individual particles of light, as well as QKD technologies, and has laid the foundations for a European measurement infrastructure able to validate the performance of QKD systems to support the development of next-generation communication systems and quantum networks. The project provided important metrological expertise to support a real-world demonstration, led by industry, of well-characterised QKD over a single field-installed lit fibre. This work makes QKD a more attractive commercial proposition and will accelerate its commercial deployment. 

EMPIR project 14IND05 MIQC2 builds on this work.