Novel optical transceivers and signaling techniques for quantum communications

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Secure communication aims at allowing confidential communication between different parties such that an unauthorized party does not have access to the content of messages. The classical secure communication schemes can be broken if an eavesdropper has a substantial amount of computational power. In contrast, in quantum secure communication also known as quantum key distribution (QKD), the security of the key can in principle be guaranteed regardless of the computational power available to the eavesdropper. In classical communication, communicating parties are not aware that an eavesdropper is accessing private information. For example, if someone is tapping into a telephone line, the communication goes on unmodified. However, in quantum communication, the leakage of information to the eavesdropper is quantitatively related to the degradation of the communication between the communicating parties. This is because any action by which the eavesdropper extracts information out of the quantum channel is a form of measurement and according to quantum physics, measurement in general modifies the state of the measured system. In this proposal, we explore novel transceivers and signaling schemes to maximize the rate of secret key transmission. We consider two types of channels - fiber optic and free space optic. In our analysis and simulation, we include the distortions and noise introduced by the channels and we also introduce digital equalizers to mitigate the channel impairments. We estimate the bit error rate and mutual information between the communicating parties in the presence/absence of the eavesdropper. Once the parameters are optimized using our simulation tools, experiments will be carried out with the help of our international collaborator. The expected outcomes are (i) novel optical transceivers, and (ii) new modulation schemes that provide longer distances and/or higher security will be developed. The Canadian industries and defense organizations benefit from this research because a higher secret key rate could be useful in fighting against hackers and cyber fraud.