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Physical Review Letters

Differential Phase Shift Quantum Key Distribution

Kyo Inoue, Edo Waks A, Y. Yamamoto

Published Jun 27, 2002• 483 citations
Publisher

Abstract

A novel quantum cryptography scheme is proposed, in which a single photon is prepared in a linear superposition state of three basis kets. A photon split to three pulses is sent from Alice to Bob, where the phase difference between sequential two pulses carries bit information. Bob measures the phase difference by passive differential phase detection. This scheme is suitable for fiber transmission systems and offers a key creation efficiency higher than conventional fiber-based BB84.

DOI
10.1103/physrevlett.89.037902

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A novel quantum cryptography scheme is proposed, in which a single photon is prepared in a linear superposition state of three basis kets. A photon split to three pulses is sent from Alice to Bob, where the phase difference between sequential two pulses carries bit information. Bob measures the phase difference by passive differential phase detection. This scheme is suitable for fiber transmission systems and offers a key creation efficiency higher than conventional fiber-based BB84.
This paper presents novel quantum key distribution (QKD) schemes that use differential phases of sequential pulses as an information carrier. Alice sends a photon in a linear superposition state of three temporal slots, in which each amplitude is phase-modulated by {0,π}. Bob measures the phase difference of an asymmetric interferometer, and tells Alice time-instance at which the photon was counted. From this time information and her modulation data, Alice knows which detector counted the photon in Bob s site. Then, the two parties create a secret key. The scheme is suitable for fiber transmission systems and offers key creation efficiency higher than conventional phase-encoding QKD. The above scheme utilizes fully non-orthogonal four states. Differential phase shift QKD utilizing two non-orthogonal states is also presented. Alice sends a coherent pulse train with less than one photon per pulse, which is phase modulated by {0,π} for each pulse, and Bob measures the pulse train by a one-bit delay circuit. The system has a simple configuration such that Alice has no interferometer and sends no intense reference pulse, unlike to conventional QKD scheme using two non-orthogonal states, and also has an advantage of high key creation efficiency.
We propose a scheme for quantum key distribution, in which single photons are encoded with polarization states and then divided and delayed to encode phase differences between two sequential pulses. In an example, the BB84 and DPS (differential phase shift) protocols are combined to achieve single-photon two-qubit quantum key distribution. This scheme can increase the key generation efficiency up to 7/6, higher than that of the conventional single-photon one-qubit quantum key distribution scheme.
Differential-phase-shift quantum key distribution based on two nonorthogonal states is described. A weak coherent pulse train is sent from Alice to Bob, in which the phase of each pulse is randomly modulated by ${0,\ensuremath{\pi}}.$ Bob measures the differential phase by a one-bit delay circuit. The system has a simple configuration without the need for an interferometer and a bright reference pulse in Alice's site, unlike the conventional QKD system based on two nonorthogonal states, and has an advantage of improved communication efficiency. The principle of the operation is successfully demonstrated in experiments.
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.
We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors of 2 and 3, respectively. For N(≥3)-period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum-memory-based long-distance fiber communication systems.