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Quantum Electronics and Laser Science Conference

Secret key distribution using differential-phase-shift keyed macroscopic coherent light

Kyo Inoue, Shusaku Hayashi

Published May 1, 2007• 2 citations
Publisher

Abstract

A quantum key distribution scheme utilizing quantum noise is proposed. It uses macroscopic coherent light that is phase-modulated by {-δ, δ} and direct differential detection. It has possibility for high data rate.
DOI
10.1109/qels.2007.4431647

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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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Quantum key distribution is used for secure communication between two parties for generation of secret key. Differential Phase Shift Quantum Key Distribution is a new and unique QKD protocol that is different from traditional ones, providing simplicity and practicality. This paper presents Delay Selected DPS-QKD scheme in which it uses a weak coherent pulse train, and features simple configuration and efficient use of the time domain. All detected photon participate to form a secure key bits and resulting in a higher key creation efficiency.
Differential phase shift quantum key distribution systems have a high potential for achieving high speed key generation. However, its unconditional security proof is still missing, even though it has been proposed for many years. Here, we prove its security against collective attacks with a weak coherent light source in the noiseless case (i.e., no bit error). The only assumptions are that quantum theory is correct, the devices are perfect and trusted and the key size is infinite. Our proof works on threshold detectors. We compute the lower bound of the secret key generation rate using the information-theoretical security proof method. Our final result shows that the lower bound of the secret key generation rate per pulse is linearly proportional to the channel transmission probability if Bob's detection counts obey the binomial distribution.