Error performance of semi-classical quantum receivers for CPPM signals in KCQ key generation

Properties of the keyed communication in quantum noise (KCQ) key generation by coherent pulse position modulation (CPPM) are considered. We derive the error performance of an eavesdropper using the square-root measurement for 2-CPPM, the so-called 2-slot amplitude-shift-keying, with a very short initial key. We consider individual and collective semi-classical quantum receivers as the attacker's receivers.