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Journal of Lightwave Technology

Quantum key distribution by a free-space MIMO system

Motti Gabay, Shlomi Arnon

Published Aug 1, 2006• 44 citations
Publisher

Abstract

Quantum key distribution (QKD) systems for use in future free-space optical communication links restrict communication to a low bit rate. In this paper, increasing the QKD bit rate using a communication system that includes a multiple-input-multiple-output quantum key distribution (MQKD) is proposed. Such a system can enable a number of receivers to communicate simultaneously with a number of transmitter elements, which consequently increases the overall QKD bit rate. However, due to scattering and turbulence in the atmospheric channel, this method may introduce interference effects when a photon transmitted from one transmitter element reaches the wrong detector element in the receiver. These interference effects reduce the system bit rate and increase the quantum bit error rate. A novel mathematical model for analyzing the effect of crosstalk and interference on the MQKD system performance is derived. The results of the analysis indicate that atmospheric effects impair performance. In order to mitigate the atmospheric effect, using several wavelengths simultaneously is suggested. Criteria to define the number of wavelengths that are required to achieve a given performance are also provided.

DOI
10.1109/jlt.2006.878043

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Quantum key distribution (QKD) systems for use in future free-space optical communication links restrict communication to a low bit rate. In this paper, increasing the QKD bit rate using a communication system that includes a multiple-input-multiple-output quantum key distribution (MQKD) is proposed. Such a system can enable a number of receivers to communicate simultaneously with a number of transmitter elements, which consequently increases the overall QKD bit rate. However, due to scattering and turbulence in the atmospheric channel, this method may introduce interference effects when a photon transmitted from one transmitter element reaches the wrong detector element in the receiver. These interference effects reduce the system bit rate and increase the quantum bit error rate. A novel mathematical model for analyzing the effect of crosstalk and interference on the MQKD system performance is derived. The results of the analysis indicate that atmospheric effects impair performance. In order to mitigate the atmospheric effect, using several wavelengths simultaneously is suggested. Criteria to define the number of wavelengths that are required to achieve a given performance are also provided.
Quantum key distribution (QKD) systems are being developed for possible use in future free space optical communication links to provide high security transmissions. However, these systems restrict the communication to a low bit-rate. To increase the QKD bit rate we suggest implementing a communication system which includes both optical detector and transmitter arrays. The mathematical description of this scheme involves a multi-input multi-output (MIMO) model. The optical detector and transmitter arrays enable the receiver to communicate simultaneously with a number of transmitter elements, which consequently increases the QKD bit rate. However, this method may introduce interference effects when a photon transmitted from one transmitter element reaches the wrong detector element in the receiver, due to scattering and turbulence in the atmospheric channel. This crosstalk and interference reduce the overall system bit rate and increase the quantum bit error rate (QBER). Analyzing the effect of crosstalk and interference on the system performance is accomplished by using the optical transfer function (OTF) theory.
Multiphoton Quantum Key Distribution (QKD) has recently been proposed to exchange the secret keys using the rotational of polarization over a multi-stage protocol. It has the ability to outperform the weaknesses of a single photon QKD by improving the generation of key rate and distance range. This paper investigates the theoretical aspects of multiphoton QKD protocol’s performance over free space optic (FSO) networks. The most common setup for quantum communication is the single-beam approach. However, the single-beam setup has limitations in terms of high geometrical loss. In this paper, the symmetry multiple-beam for quantum communication which is called as Multiphoton Quantum Communication-Multiple Beam (MQC-MB) is proposed to transmit the multiphoton from the sender to the receiver in order to minimize the impact of geometrical loss that is faced by the single-beam setup. The analysis was carried out through mathematical analysis by establishing the FSO quantum model with the effects of atmospheric and geometrical loss as well as considering atmospheric turbulence modeled by log-normal distribution. The design criteria of FSO, such as the transmitter, receiver, beam divergence, and diameter of apertures, are analytically investigated. The numerical results demonstrate that the MQC-MB outperforms the single-beam in terms of reducing channel loss by about 8 dB and works well under strong turbulence channel. Furthermore, the MQC-MB reduces the quantum bit error rate (QBER) and improves the secret key rate (SKR) as compared to the single-beam system even though the distance between the sender and receiver increases.
In this paper, a free-space quantum key distribution (QKD) system based on BB84 protocol is studied assuming that the transmitted quantum bits are multiplexed spatially based on orthogonal orbital angular momentum (OAM) carrying beams. The performance of such a system is estimated in terms of quantum bit error rate, outage capacity, and effective data rate taking into account the impact of error correction and privacy amplification. Based on the simulation of OAM-carrying beam propagating through atmospheric channels impaired by turbulence, the crosstalk among the multiplexed channels are investigated and its effect on the performance of the QKD system is evaluated. The presented results provide insight into the efficient design of such multiplexed QKD systems particularly in terms of the choice of the optimal average photon number per pulse and the multiplexing mode set.
We devoted to analyzing information transfer in quantum channels in terms of the performance of quantum key distribution (QKD) free-space optical (FSO) communication systems through Bennett and Brassard 84 (BB84) protocol by taking into account the combined effect of attenuation, turbulence, pointing error, and angle of arrival (AOA) fluctuations. Path loss is modeled by Beer-Lambert law, and the turbulent channel is assumed to be Fisher-Snedecor F distributed. The pointing error and AOA fluctuations are modeled by Hoyt and Rayleigh distributions, respectively. The error and sift probabilities, quantum bit error rate, and secret key rate of a QKD FSO system are obtained in analytical form, and results are presented depending on various parameters. It is shown that increased beam waist, beam deviation, AOA fluctuations, and propagation distance cause performance degradation and less secure information transmission. However, an increase in the ratio of horizontal and vertical beam misalignments, field of view, average photon number per pulse, visibility of the atmospheric environment, and optical beam wavelength impact the performance of QKD FSO systems positively. The effect of the turbulence structure constant is observed to be modest on the performance of the QKD FSO system.
Quantum safety communications is a process of quantum key distribution （QKD）. Current QKD technology restricts transmission to a low bit rate. To improve the QKD bit rate and develope high rate and large capacity, we propose a multiple-input-multiple-output（MIMO） quantum key distribution system. The Wigner operator of multi-photon entangled states in MIMO quantum key distribution channel is presented. As a result, the Wigner function of multi-photon double-model squeezed entangled sates and MIMO quantum key distribution channel capacity are also obtained, which will provide theoretical support and technical basis for developing robust space-time processing algorithm of MIMO quantum safety communications and designing optimum high performance system of MIMO quantum key distribution.
Quantum communication is a process of quantum key distribution （QKD）. Current QKD technology restricts communication to a low bit rate. To improve the QKD bit rate and develop high rate and capacity, we propose a multiple-input-multiple-output quantum key distribution system. However, quantum field itself inevitably involves quantum noise （which is determined by the quantum mechanics ）, which restrains the increase of capacity, and limits space resource utilization, that is, the problem of spatial degrees of freedom arises. The quantumization of the photon field and the electromagnetic wave equation satisfying the Schrdinger equation condition are adopted to investigate the upper bound of the spatial degrees of freedom for MIMO quantum channels, which will provide theoretical support and technical basis for developing robust space time processing algorithm for MIMO quantum communication and designing high performance systems.