arXiv subjects
Publications and source records attributed to Toshio Hasegawa.
Heralding of single photon at 1550 nm from pump pulsed non degenerate spontaneous parametric downconversion is demonstrated. P(1) and P(2) of our source are 0.1871 and 2.4 x 10 ^-3 respectively. Triggering of our source is 2.16 x 10^5 trigger.s^-1. This source may be used in QKD system.
New quantum cryptography, often called Y-00 protocol, has much higher performance than the conventional quantum cryptographies. It seems that the conventional quantum cryptographic attacks are inefficient at Y-00 protocol as its security is based on the different grounds from that of the conventional ones. We have, then, tried to cryptoanalyze Y-00 protocol in the view of cryptographic communication system. As a result, it turns out that the security of Y-00 protocol is equivalent to that of classical stream cipher.
Multiphoton state in quantum cryptography decreases its security. Key disclosing with universal quantum cloning machine (UQCM) is considered in explicit manner. Although UQCM cannot make perfect clones, there is some invariant quantity between the original photon and the imperfect clones. The invariant quantity, the direction of Stokes parameters, tells us the auxiliary information leading into key information. The attack, then, corresponds to some kind of quantum non-demolition measurement. Its application to recent high-performance quantum cryptography, Y-00 protocol, is also studied.
`Circular type' interferometric system for quantum key distribution is proposed. The system has naturally self-alignment and compensation of birefringence and also has enough efficiency against polarisation dependence. Moreover it is easily applicable to multi-party. Key creation with 0.1 photon per pulse at a rate of 1.2KHz with a 5.4% QBER over a 200m fiber was realized.