QUASAR weekly seminar talk.

• Date: Friday, November 7, 2025
• Time: 1:00 PM ET
• Location: Virtual
• Speaker: Amir Arqand
• Affiliation: University of Waterloo

Abstract

Quantum Key Distribution (QKD) aims to establish an information-theoretically secure key between two parties, Alice and Bob, by exploiting the fundamental principles of quantum mechanics. A central challenge in QKD is to provide finite-size security proofs against the most general class of attacks known as coherent attacks. One powerful approach for such proofs is based on the Entropy Accumulation Theorem (EAT). However, traditional EAT-based techniques face two major drawbacks: first, the resulting bounds on the secret key length are often suboptimal; and second, when applied to Prepare-and-Measure protocols, they introduce a practical limitation that restricts the signal-sending rate. In this presentation, I introduce a framework that extracts nearly optimal key rates from all EAT-based proof techniques, together with a new variant of the entropy accumulation theorem that addresses this limitation.

This talk is based on two papers: https://arxiv.org/abs/2502.02563 and https://arxiv.org/abs/2405.05912