Measurement-Device-Independent Quantum Key Distribution (MDI QKD)

Lead Research Organisation: University of Cambridge
Department Name: Engineering


QKD is currently the most appealing approach for the secure exchange of a secret key. It removes the vulnerabilities of current classical key distribution methods by providing theoretical security based on the principles of quantum mechanics. However, in real-world implementations, QKD is susceptible to information stealing attacks due to the imperfect nature of the devices utilised. MDI QKD removes the need for a secure detection station which is believed to be the main vulnerability of QKD systems, by transforming it into a transmission station. It however requires the preparation of almost-perfect states and the use of high count rate single photon detection technologies. Previous work carried out within the Engineering Department and Toshiba CRL, has successfully reported methods, via proof-of-principle demonstrations, that satisfy the imposed limitations and produce high key rates. Such methods include the utilisation of gain switched seeded lasers as a way of creating weak coherent pulses that almost perfectly interfere and of self-differencing avalanche photo diodes and superconducting nanowire single photon detectors for high key rates and efficiency at room temperatures.
The project will be focused on the design and optimisation of an MDI QKD system based on previous research, for real life implementation. There is a vast amount of parameters that change in this concept. The aim of this project is to take account of the restrictions of MDI QKD in real situations to progress the current literature, while improving and characterising the optoelectronics used. One of the main issues that needs to be countered is the dramatic and inevitable increase of transmission distances for useful MDI QKD. This deteriorates the conditions under which the system operates and therefore necessitates the development of feedback loops with high stability. Additionally, the synchronisation of the sources and the receiver using a master clock is not viable and alternative methods need to be devised, for example utilising multiplexing. A crucial feature of an implemented MDI QKD is automaticity with real time data analysis and state modulation. Consequently, the development of a code that will drive the suitable optoelectrical components to function and recalibrate the instruments during the run period is mandatory. It is also very significant that true random number generators are used for the selection of bases, bits and any other parameters imposed by the protocols. These generators exploit physical phenomena, usually of quantum nature, that are known to be random and therefore guarantee that their output is completely uncorrelated and unpredictable. Research into true random number generation methods should be carried out to deduce the appropriate method that will optimise the key rates, cost, efficiency and size of the system. Finally, the proof-of-principle demonstrations do not include protection against possible attacks like the Trojan horse, rendering them unfit for commercialisation. Therefore the purpose of the research is not solely to optimise the system under field conditions but additionally to increase its security against hacking attempts.
There are various further ideas that could be researched, depending on the progress and outcomes of the work carried out. Such concepts include the photonic integration of the system or its development into a star shaped network of multiple sources. The collective aim of the project however, remains within the quantum optics and information research area.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510440/1 01/10/2016 30/09/2021
1773284 Studentship EP/P510440/1 01/10/2016 30/09/2020 Mariella Minder
Description My research on MDI QKD has focused on the special MDI protocol TF QKD. The objectives set changed with the publication of this protocol. What has been achieved up to this day is a completely development of a setup able to perform TF QKD (first one ever developed). A proof of principle demonstration of TF QKD has been published in which we have shown for the first time that a certain theoretical limit on the QKD secret key rate vs attenuation can be overcome by the implementation of this protocol. As a side project, during the development of the TF QKD experiment, the research funded through this grant has aided in an investigation of Sagnac interferometers used as intensity modulators in GHz quantum communication systems, showing high stability by operating/building the interferometer in a certain way.
Exploitation Route We have shown a setup that can be used to perform TF QKD that utilises certain methods which can be useful for others looking into developing quantum protocols. The data itself given in the paper can be used as a sort of reference to test different versions of th protocol and security analyses that keep coming up. More importantly we have shown a way in which QKD can distribute secret keys faster and for longer distances in fibre and other may use our approach to progress this even further with the ultimate goal of commercialising this technology in time for quantum supremacy.
Sectors Digital/Communication/Information Technologies (including Software)