PhD defence by Ronny Müller

Abstract

Privacy and secure communication are a cornerstone of our digital society. While for decades our messages and information have been kept secret using public-key cryptosystems, our communications are now in danger with the emergence of the “quantum threat.” With the development of increasingly more powerful quantum computers, our formerly secure communications are at risk of being decoded by malicious eavesdroppers in the not-so-distant future. A possible solution to the quantum threat is the use of Quantum Key Distribution (QKD) as a replacement for our classical communication systems. QKD exploits the properties of quantum mechanics to distribute a secret key between two parties with a guarantee of security against any eavesdropper, no matter how technologically advanced they are—assuming they are all-powerful but constrained by the laws of physics.

While the physical phase of QKD distributes keys between different parties, these keys can still have slight mismatches due to noise or eavesdropping attempts. A crucial step before the secret keys can be used to encrypt our data is therefore error correction, during which these mismatches are corrected. Importantly, the task of error correction is complicated by the requirements of secrecy; one must leak as little information about the secret keys as possible while trying to find and correct all errors. Our research investigated and developed new algorithms for this error correction stage in QKD, with a special focus on high-dimensional QKD, in which properties of high-dimensional quantum states are leveraged to increase performance.

Supervisors

• Principal supervisor: Professor Søren Forchhammer, Department of Electrical and Photonics Engineering, DTU, Denmark
• Co-supervisor: Associate Professor Davide Bacco, Department of Physics and Astronomy, University of Florence, Italy
• Co-supervisor: Professor Leif Oxenløwe, Department of Electrical and Photonics Engineering, DTU, Denmark

Evaluation Board

• Associate Professor Tobias Gehring, Department of Physics, DTU, Denmark
• Associate Professor David Elkouss, Okinawa Institute of Science and Technology, Japan
• Senior Researcher Marco Ferrari, CNR, Istituto di Elettronica e Ingegneria dell’Informazione e delle Telecomunicazioni, Italy

Master of the Ceremony

• Associate Professor Michael Galili, Department of Electrical and Photonics Engineering, DTU, Denmark