A quantum secret sharing (QSS) protocol based on a differential-phase-shift scheme is proposed, which quantum mechanically provides a full secret key to one party and partial keys to two other parties. A weak coherent pulse train is utilized instead of individual photons as in conventional schemes. Compared with previous QSS protocols, the present one features a simple setup, is suitable for fiber transmission, and offers the possibility for a high key creation rate. An experiment is also carried out to demonstrate the operation.
Since it was noted that quantum computers could break public key cryptosystems based on number theory, extensive studies have been undertaken on quantum cryptography, which offers unconditionally secure communication based on quantum mechanics. We investigate a quantum key distribution (QKD) scheme using macroscopic coherent light with optically pre-amplified direct differential detection. A transmitter “Alice” sends a series of two macroscopic nonorthogonal coherent states that partially overlap due to quantum noise. A receiver “Bob” amplifies and receives it with direct differential detection followed by a thresholding process. To avoid difficulties in detection, our scheme uses conventional direct differential photodetection, not single-photon detection or homodyne detection as in previous QKD protocols. System performance assuming some eavesdropping is evaluated, the results of which suggest that our scheme is usable for short or medium distance.
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