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arXiv:1109.2495 · Europhysics Letters (EPL)

Continuous variable quantum key distribution based on optical entangled states without signal modulation

Xiaolong Su, Wenzhe Wang, Yu Wang, Xiaojun Jia, Changde Xie, Kunchi Peng

Published Jul 1, 2009• 45 citations
arXivHTMLPDF

Abstract

In this paper, we present the first experimental demonstration on continuous variable quantum key distribution using determinant Einstein-Podolsky-Rosen entangled states of optical field. By means of the instantaneous measurements of the quantum fluctuations of optical modes, respectively, distributed at sender and receiver, the random bits of secret key are obtained without the need for signal modulation. The post-selection boundaries for the presented entanglement-based scheme against both Gaussian collective and individual attacks are theoretically concluded. The final secret key rates of 84 kbits/s and 3 kbits/s are completed under the collective attack for the transmission efficiency of 80% and 40%, respectively.

DOI
10.1209/0295-5075/87/20005

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In this paper, we present the first experimental demonstration on continuous variable quantum key distribution using determinant Einstein-Podolsky-Rosen entangled states of optical field. By means of the instantaneous measurements of the quantum fluctuations of optical modes, respectively, distributed at sender and receiver, the random bits of secret key are obtained without the need for signal modulation. The post-selection boundaries for the presented entanglement-based scheme against both Gaussian collective and individual attacks are theoretically concluded. The final secret key rates of 84 kbits/s and 3 kbits/s are completed under the collective attack for the transmission efficiency of 80% and 40%, respectively.
We proposed a scheme of continuous-variable quantum key distribution, in which the bright Einstein-Podolsky-Rosen entangled optical beams are utilized. The source of the entangled beams is placed inside the receiving station, where half of the entangled beams are transmitted with round trip and the other half are retained by the receiver. The amplitude and phase signals modulated on the signal beam by the sender are simultaneously extracted by the authorized receiver with the scheme of the dense-coding correlation measurement for continuous quantum variables, thus the channel capacity is significantly improved. Two kinds of possible eavesdropping are discussed. The mutual information and the secret key rates are calculated and compared with those of unidirectional transmission schemes.
We present and demonstrate a high-efficiency and compact scheme for generating Gaussian-modulated Einstein-Podolsky-Rosen (EPR) entangled optical fields by injecting a modulated signal field into a non-degenerate optical parametric amplifier (NOPA). We perform a quantum analysis of the scheme and derive the variance of the output signal (idler) mode and the quantum entanglement between the signal and idler modes from the NOPA. An experimental study is presented with different Gaussian modulation depths, showing that the modulation of the injected signal field successfully enlarges the distribution of the field quadratures of the EPR source in phase space and has a negligible effect on the entanglement quality. The experimental observations have good agreement with the theoretical analysis. Our scheme can be used readily in continuous variable quantum key distribution protocol.
We study a new quantum cryptography protocol with continuous variables for the construction of secret quantum keys. The protocol is based on pairs of Einstein-Podolsky-Rosen entangled quadratures of a two-mode electromagnetic field generated by non-degenerate parametric amplification. Instantaneous measurements of the quantum fluctuations provide the random bits of the secret key. The irreversible alteration of the quadrature entanglement due to unauthorized measurements immunizes the quantum key distribution against eavesdropping attacks. Based on two identical non-degenerate parametric amplifiers, the protocol circumvents the usual 50% bits rejection due to base incompatibility during the key generation process, and avoids the need for homodyne detection schemes which are highly sensitive to the mode matching problems.
We study a new quantum cryptography protocol with continuous variables for the construction of secret quantum keys. The protocol is based on pairs of Einstein-Podolsky-Rosen entangled quadratures of a two-mode electromagnetic field generated by non-degenerate parametric amplification. Instantaneous measurements of the quantum fluctuations provide the random bits of the secret key. The irreversible alteration of the quadrature entanglement due to unauthorized measurements immunizes the quantum key distribution against eavesdropping attacks. Based on two identical non-degenerate parametric amplifiers, the protocol circumvents the usual 50% bits rejection due to base incompatibility during the key generation process, and avoids the need for homodyne detection schemes which are highly sensitive to the mode matching problems.
We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of 46.846.846.8 kbits/s against collective attacks at an encoding rate of 101010 MHz for a 9090%90 channel loss when the modulation variance is optimal.
We experimentally demonstrate a complete, end-to-end, quantum key distribution system using a continuous wave laser and standard optical components. Our implementation encodes random bits as weak Gaussian modulations onto the phase and amplitude quadratures of the laser beam. We process data from the quantum channel using a post-selection procedure and subsequently apply information reconciliation and privacy amplification procedures to generate an absolutely secure secret key. The maximum information that an eavesdropper may have obtained about this secret key, from the quantum channel and classical communications, is bounded to below one bit. Under the assumption of individual Gaussian eavesdropping attacks, we achieve a secret key generation rate of 25 Mbits/s for a lossless channel and 1 kbit/s for 90% channel loss, per 17 MHz of detected bandwidth.