Shlok Ashok Nahar

We provide a security proof for quantum key distribution (QKD) protocols using passive detection setups within the entropic uncertainty relation (EUR) framework. Passive detection avoids the need for active basis choice but introduces challenges due to beam splitters and imperfections in detectors. We show how to define and bound the phase-error rate in passive detection setups, even when detector imperfections are not precisely known but lie within known ranges. Our analysis applies in the finite-size regime against general coherent attacks.

The coherent one-way (COW) protocol is a promising commercial solution to practical quantum key distribution (QKD) due to its simple optical implementation. However, the non-IID structure of COW due to its inter-signal coherence makes standard security analysis inapplicable. Recently, it has been shown that a modified COW setup allows standard IID analysis, but at the cost of imposing extra limitations and increasing the number of pulses required for each bit. Here we propose a variant that possesses the IID structure and completely retains the optical setup of COW, but with a different data processing scheme that ignores inter-signal information. We obtain key rate lower bound close to analysis for the previously proposed IID variant, and achieves a higher number of key bits transmitted per second.