Doctoral Dissertations
Date of Award
5-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Physics
Major Professor
George Siopsis
Committee Members
Stefan Spanier , Gong Gu, Jaan Mannik
Abstract
Quantum Key Distribution (QKD) ensures security by relying on the laws of quantum physics rather than the mathematical intricacy of encryption algorithms. The transmission medium is a critical restricting factor for any quantum communication protocol. Fiber-based optical networks suffer great losses, making quantum communication impossible beyond metropolitan scales. Here free-space quantum communication can be a great alternative for long-distance communication. Even though modern Communications are mostly wireless the atmosphere poses a challenge for QKD. So QKD must be resistant to both atmospheric loss and variations in transmittance. In this thesis we conduct an experiment to strengthen the BB84 protocol's resistance to turbulence by tracking the channel's transmittance, identifying when the transmittance is low which leads to a high error rate, and discarding those data using Prefixed-Threshold Real-time Selection (P-RTS).
In the real world, QKD systems rely on practical imperfect devices that introduce security flaws, such as side-channel attacks, that can be exploited by a potential eavesdropper. Measurement Device Independent (MDI) QKD allows an untrusted third party to make measurements, thus eliminating all side-channel attacks. So far, MDI QKD implementations have been carried out in near symmetric channels, which are challenging to implement in real-world settings because of varying channel losses caused by geographic location. In a maritime environment or satellite-based communication, a QKD system can be highly asymmetric, with continuously changing losses in the different channels. In this work, we used an Acousto-Optic Modulator (AOM) to perform asymmetric MDI-QKD in a laboratory environment with simulated turbulence to investigate the performance of free-space quantum communication. Scattering and beam wandering fluctuate the intensity in turbulent conditions which lowers the signal-to-noise ratio. We demonstrated an improvement in the key rate under moderate turbulent conditions and a very lossy channel for finite-size decoy-state MDI QKD using Wang et al.'s 7-intensity optimization method combined with P-RTS. Furthermore, we demonstrated that P-RTS can produce significantly higher secure key rates across a broad spectrum of atmospheric channel parameters.
Recommended Citation
Reaz, Kazi MH, "Experimental Quantum Key Distribution in Turbulent Channels. " PhD diss., University of Tennessee, 2024.
https://trace.tennessee.edu/utk_graddiss/10075