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Physical Review A

Quantum key distribution with a single photon from a squeezed coherent state

Masahiro Matsuoka, Takuya Hirano

Published Apr 15, 2003• 20 citations
Publisher

Abstract

Squeezing of the coherent state by optical parametric amplifier is shown to efficiently produce single-photon states with reduced multiphoton probabilities compared with the weak coherent light. It can be a better source for a longer-distance quantum key distribution and also for other quantum optical experiments. The necessary condition for a secure quantum key distribution given by Brassard et al. is analyzed as functions of the coherent-state amplitude and squeeze parameter. Similarly, the rate of the gained secure bits G after error correction and privacy amplification given by L\"utkenhaus is calculated. Compared with the weak coherent light, it is found that G is about ten times larger and its high level continues on about two times longer distance. By improvement of the detector efficiency it is shown that the distance extends further. Measurement of the intensity correlation function and the relation to photon antibunching are discussed for the experimental verification of the single-photon generation.

DOI
10.1103/physreva.67.042307

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Squeezing of the coherent state by optical parametric amplifier is shown to efficiently produce single-photon states with reduced multiphoton probabilities compared with the weak coherent light. It can be a better source for a longer-distance quantum key distribution and also for other quantum optical experiments. The necessary condition for a secure quantum key distribution given by Brassard et al. is analyzed as functions of the coherent-state amplitude and squeeze parameter. Similarly, the rate of the gained secure bits G after error correction and privacy amplification given by L"utkenhaus is calculated. Compared with the weak coherent light, it is found that G is about ten times larger and its high level continues on about two times longer distance. By improvement of the detector efficiency it is shown that the distance extends further. Measurement of the intensity correlation function and the relation to photon antibunching are discussed for the experimental verification of the single-photon generation.
Generation and application of squeezed light source has been the interest in the field of quantum optical experiments, especially with regards to the field of quantum key distribution. In this paper, a method using phase-squeezed state as the input state of the single photon quantum key distribution protocol is introduced, and the rate of the gained secure key of the proposed method after the post-processing techniques is analyzed. Compared to the conventional quantum key distribution protocol using weak coherent light source as the single photon source, it is shown that in the proposed method there are significant improvements in both the transmittable distance and the gained secure key rate.
A highly attenuated laser pulse which gives a weak coherent state is widely used in quantum key distribution (QKD) experiments. A weak coherent state has multi-photon components, which opens up a security loophole to the sophisticated eavesdropper. With a small adjustment of the hardware, we prove that the decoy state method can close this loophole and substantially improve the QKD performance. We also propose a few practical decoy state protocols, study statistical fluctuations and perform experimental demonstrations. Moreover, we apply the methods from entanglement distillation protocols based on two-way classical communication to improve the decoy state QKD performance. Furthermore, we study the decoy state methods for other single photon sources, such as triggering parametric down-conversion (PDC) source. We propose a model and post-processing scheme for the entanglement-based QKD with a PDC source. Although the model is proposed to study the entanglement-based QKD, we emphasize that our generic model may also be useful for other non-QKD experiments involving a PDC source. By simulating a real PDC experiment, we show that the entanglement-based QKD can achieve longer maximal secure distance than the single-photon-based QKD schemes. We present a time-shift attack that exploits the efficiency mismatch of two single photon detectors in a QKD system. This eavesdropping strategy can be realized by current technology. We also discuss counter measures against the attack and study the security of a QKD system with efficiency mismatch detectors.
We propose a high security quantum key distribution (QKD) scheme utilizing one mode of spontaneous parametric downconversion gated by a photon number resolving detector. This photon number measurement is possible by using single-photon detectors operating at room temperature and optical fibers. By post selection, the multiphoton probability in this scheme can be reduced to lower than that of a scheme using an attenuated coherent light resulting in improvement of security. Furthermore, if distillation protocol (error correction and privacy amplification) is performed, the gain will be increased. Hence a QKD system with higher security and bit rate than the laser-based QKD system can be attained using present available technologies.
In this paper we investigate the security of continuous variable BB84 quantum key distribution protocol using single photon added then subtracted squeezed coherent state SPASSCS. It's found that the SPASSCS is a non-Gaussian and nonclassical state. Its non-Gaussianity and non-classicality are exhibited via the Wigner function. It's shown that the proposed state is generally robust against the eavesdropping strategies, such as intercept-resend attack and superior channel attack. Further, a comparative study has proved the strong efficiency of the proposed state over coherent state, squeezed coherent state and photon added then subtracted coherent state. Our analysis employs bit error rate, mutual information, and secure key gain.
Quantum key generation rate of decoy state quantum key distribution(QKD) with a heralded single-photon source(HSPS) is deduced.Relationship between quantum key generation rate and detection efficiency of sender is discussed.Optimal intensities and key generation rate of decoy state QKD with a weak coherent pulse(WCP) and an HSPS are analyzed.It shows that key generation rate increases with increase of detection efficiency of sender and its security distance is the same as with a perfect single photon source.Decoy state QKD increases security distance and key rate of QKD.Due to less dark counts QKD with HSPS works longer distance than WCP.
Since the single photon is easy to attenuate and be disturbed, its key generation rate and transmission distance in quantum communication systems are generally limited. In contrast, weak coherent pulse (WCP) and heralded single photon source (HSPS) exhibit higher feasibility than the single photon source in quantum key distributions (QKD). We compare the performances of QKD using these two kinds of photon sources and decoy state method, incorporating data-postprocessing methods including the Lütkenhaus scheme and Gottesman-Lo-Lütkenhaus- Preskill (GLLP) scheme. Simulation results indicate that QKD using HSPS can transmit longer distance than using WCP with lower overall quantum bit error rate (QBER) at the same transmission distance, albeit with relatively low key generation rate.