Philip Sibson

Measurement-device-independent quantum key distribution (MDI-QKD) offers a method of distributing shared randomness for use in symmetric key cryptography, while integrated optics provides a promising platform for ubiquitous quantum communication. This work experimentally demonstrates the use of indium phosphide (InP) devices for MDI-QKD. We generate 100 ps pulses for 2 GHz clocked, time-bin encoded BB84 states with random phases through a novel gain switching technique. By interfering two independent InP devices, we achieve 50 bps at 100 km and pre-empt the availability of integrated receivers which will increase rates through inherent scalability.

We have come a long way since the first implementation of a quantum key distribution (QKD) system and various attacks have been demonstrated, such as the Trojan Horse Attack (THA). In this attack, the eavesdropper Eve gains information by analysing the back-reflections of light she shines into the QKD system. Almost all attacks have been demonstrated on devices based on fibre components. However, the first chip-scale QKD devices are being developed now, utilising the small size of integrated optics, the stability of the optical system and the ease at which it can be mass-produced, showing great commercial potential. Here we discuss a THA on chip-scale QKD. First, points of reflection in a QKD transmitter chip were found via a reflectometry. Based on this we give an experimental set-up to implement a THA which would give Eve access to 50% of the key. Full experimental results of this attack are expected in the next two to three months.

As computing becomes more mobile, cashless as well as cardless payment solutions are introduced and a need arises for incorporating QKD in a mobile device. Handheld devices present a particular challenge as the orientation and the phase of a qubit will depend on device motion. This problem is addressed by the reference frame independent (RFI) QKD scheme, providing a protocol to overcome issues with calibration and slow variations in reference frames between the two communicating parties. This indicates that the real world imperfections and the impracticality of calibrating mobile devices can be mitigated to allow the adoption of integrated quantum technologies in portable systems.