Single-photon Raman interaction for realizing the photon-number splitting attack

Photon-number splitting (PNS) attack poses a significant threat to the security of quantum key-distribution (QKD) systems that utilize weak coherent states (WCS). While this attack has been extensively explored in theory, its experimental realization remains elusive, raising questions about its practical implementation and impact. This study introduces a novel framework to experimentally demonstrate the PNS attack by leveraging single-photon Raman interaction (SPRINT), a well-developed technological capability. We analytically assess the feasibility and practical implications of this attack. Complementing our recently published analysis of the attack, ¹ in this work we calculate the detection statistics for phase-randomized WCS and analyze the purity of the quantum state post-attack. Our analysis reveals that indeed current technologies are sufficient to implement the PNS attack, but the eavesdropper's information gain deviates from theoretical ideals. Moreover, we show that the attack compromises the integrity of the quantum state, introducing a non-zero quantum bit-error rate (QBER). These findings challenge the conventional assumption of perfect information extraction by the attacker through PNS while underscoring the need for robust QKD protocols, such as the coherent one-way (COW) protocol, which are secure against PNS attacks. Beyond their implications for cryptographic security, the findings also offer new insights into fundamental quantum processes, such as single-photon subtraction and the informational changes caused by photon splitting.