CM – A quantum secure direct communication network with 15 users

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September 23, 2021

from the Chinese Academy of Sciences

Quantum Secure Direct Communication (QSDC) based on entanglement can transmit confidential information directly. Scientists in China researched a QSDC network based on time-energy entanglement and sum-frequency generation. The results show that if any two users perform QSDC over 40 kilometers of fiber, the information transfer rate can be kept at 1 Kbp / s. Our result lays the foundation for the future realization of satellite-based remote and global QSDC.

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Quantum communication has represented a revolutionary step in secure communication because of its high security of quantum information, and many communication protocols have been proposed, such as Quantum Secure Direct Communication Protocol (QSDC). QSDC based on entanglement can transmit confidential information directly. Every attack by QSDC only results in a random number and cannot obtain any useful information from it. Therefore, QSDC has simple communication steps and reduces potential security gaps and offers high security guarantees that guarantee the security and value proposition of quantum communication in general. However, the inability to simultaneously distinguish the four sets of encoded orthogonal entangled states in entanglement-based QSDC protocols limits their practical application. In addition, it is important to build a quantum network in order to enable broad applications of quantum secure direct communication. An experimental demonstration of QSDC is urgently needed.

In a new article published in Light Science & Application, a team of scientists led by Professor Xianfeng Chen of the State Key Laboratory of Advanced Optical Communication Systems and Networks , School of Physics and Astronomy, Shanghai Jiao Tong University, China, and Professor Yuanhua Li from Department of Physics, Jiangxi Normal University, China, examined a QSDC network that deals with time-energy entanglement and sum-frequency generation ( SFG) is based. You present a fully connected entanglement based QSDC network with five subnets and 15 users. Using the frequency correlations of the fifteen photon pairs over time division multiplex and density wavelength division multiplexing (DWDM), they run a 40 kilometer fiber optic QSDC experiment by implying a two-stage transmission between each user. The network processor divides the spectrum of the single photon source into 30 channels of the International Telecommunication Union (ITU). With these channels there is a coincidence event between each user by taking a Bell State measurement based on the SFG. This allows the four sets of coded entangled states to be identified simultaneously without post-selection.

It is known that the security and reliability of information transmission for QSDC is an essential part of the quantum network. Therefore, they implemented block transfer and incremental transfer methods in QSDC with the estimation of the secrecy capacity of the quantum channel. After confirming the security of the quantum channel, the legitimate user reliably performs encoding or decoding operations within these schemes.

“The results show that if any two users perform QSDC over 40 kilometers of fiber, the fidelity of the one they shared entangled state is still over 95% and the information transfer rate can be kept at 1 Kbp / s. Our result shows the feasibility of a proposed QSDC network and thus lays the foundation for the future implementation of satellite-based remote and global QSDC.

« With this scheme, each user connects to each other through shared pairs of entangled photons of different wavelengths. In addition, it is possible to improve the information transfer rate in the case of high-performance detectors to more than 100 Kbp / s as high-speed control used in the modulator, « they added.

 » It is worth noting that the present work is a point- long-distance QSDC connectivity, combined with QSDC’s recently proposed secure repeater quantum network, which provides secure end-to-end communications throughout the quantum Internet. will enable the establishment of a secure quantum network with today’s technology and exploit the great potential of QSDC in future communication, « predict the scientists.

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