Quantum Communication technology has the potential to send messages securely against any sort of hacker, no matter how powerful their computer is – even a quantum computer! The basic idea is simple. Heisenberg’s Uncertainty Principle implies that if you find out one property of a particle you necessarily create uncertainty in other properties. That is, quantum particles are disturbed by measurements. Because of this, an eavesdropper trying to read a secret message encoded in photons will leave unmistakable traces of this transgression on the message itself. These traces clearly reveal the attempt to eavesdrop, ensuring detection before any of your valuable information is compromised.

Quantum communication protocols were first developed in the 1980s. There are short-range systems in commercial operation in many countries, including an Australian one developed by CQC²T researchers. Recently ground-satellite quantum encryption links have also been demonstrated by scientists in USTC, China [Sheng-Kai Liao et al., ‘Satellite-to-ground quantum key distribution’, Nature, 2017, 549:43; Ji-Gang Ren et al., ‘Ground-to-satellite quantum teleportation, Nature, 2017, 549:70.) and MPL, Germany [K Günthner et al., ‘Quantum-limited measurements of optical signals from a geostationary satellite’, Optica, 2017, 4:611].

A grand challenge, which is being tackled worldwide, including at CQC²T, is to extend the range of secure communications into a global network. Because quantum messages cannot be copied, this requires using quantum repeaters to realise a large-scale quantum network. Analogous to the fibre repeater links in global fibre optics networks, quantum repeaters are special-purpose quantum devices that bridge a connection between a distant quantum source and receiver are critical infrastructure for a globally connected quantum network. Designing and making them – and showing their viability – is an active area of research.