A quantum secure direct communication network of 15 users

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(a) The quantum lattice is fully connected by five subnets (A, B, C, D and E are represented by red, orange, green, blue and black respectively). The dotted lines between the sub-arrays (10 links with different colors) are the correlated time-energy photon pairs between the sub-arrays. (b) Each subnet (such as subnet A) is equipped with a 1 × 3 beam splitter and delay control module, which splits a pair of entangled photons correlated with frequency (signs red and blue) and sends them to three random users. Credits: Zhantong Qi, Yuanhua Li, Yiwen Huang, Juan Feng, Yuanlin Zheng and Xianfeng Chen

Entanglement-based Quantum Secure Direct Communication (QSDC) can directly transmit confidential information. A Chinese scientist explored a QSDC network based on time-energy entanglement and sum-frequency generation. The results show that when two users perform QSDC over 40 kilometers of optical fiber, the information transmission rate can be maintained at 1 Kbp / s. Our result lays the foundation for achieving a global and long-range satellite QSDC in the future.

Quantum communication has presented a revolutionary step in secure communication due to its high security of quantum information, and many communication protocols have been proposed, such as Quantum Secure Direct Communication Protocol (QSDC). The entanglement-based QSDC can directly transmit confidential information. Any QSDC attack only results in a random number, and cannot derive any useful information from it. Therefore, QSDC has simple communication steps and reduces potential security breaches, and offers high security guarantees, which ensures the security and value propositions of quantum communications in general. However, the inability to simultaneously distinguish the four sets of orthogonal entangled states encoded in entanglement-based QSDC protocols limits its practical application. In addition, it is important to build a quantum network in order to make large applications of quantum secure direct communication. The experimental demonstration of QSDC is absolutely necessary.

In a new article published in Light science and 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 of the Department of Physics, Jiangxi Normal University, China explored a QSDC network based on time-energy entanglement and sum-frequency generation (SFG). They present a fully connected entanglement-based QSDC network comprising five subnets, with 15 users. Using the frequency correlations of the fifteen photon pairs via time division multiplexing and dense wavelength division multiplexing (DWDM), they perform a 40 kilometer fiber QSDC experiment involving two-way transmission. steps between each user. In this process, the network processor divides the spectrum of the single photon source into 30 International Telecommunication Union (ITU) channels. With these channels, there will be a coincidence event between each user performing a Bell Status measurement based on the SFG. This allows the four sets of encoded entangled states to be identified simultaneously without post-selection.

It is well known that the security and reliability of information transmission for QSDC is an essential element in the quantum network. Therefore, they implemented block transmission and step-by-step transmission methods in QSDC with estimation of the privacy capacity of the quantum channel. After confirming the security of the quantum channel, the legitimate user performs encoding or decoding operations within these patterns reliably.

A quantum secure direct communication network of 15 users

(a) The physical structure of the quantum network. The spectrum is divided into 30 ITU grid channels via a 100 GHz DWDM. CH17 to CH31 are numbered 1 to 15 respectively, and opposite sign numbers denote channels CH33-CH47. The wavelength allocation architecture is omitted in small trapezoidal multiplex blocks. Each small block with colored number symbols builds a group of wavelengths distributed by the network processor. (b) Each pair of signal photon and free photon is indicated by the same color bars with and without opposite numeric sign. (c) Illustration of SFG progress. Photons generated in pairs by a spontaneous parametric down-conversion process are multiplexed in the SFG experiment to achieve quantum encoding and communication. Credits: Zhantong Qi, Yuanhua Li, Yiwen Huang, Juan Feng, Yuanlin Zheng and Xianfeng Chen

These scientists summarize the results of their network diagram experiment:

“The results show that when two users perform a QSDC over 40 kilometers of optical fiber, the fidelity of the entangled state they share is always above 95%, and the information transmission rate can be maintained at 1 Kbp / s. Our result demonstrates the feasibility of a proposed QSDC network and therefore lays the foundation for achieving a global and long-haul satellite QSDC in the future. “

“With this scheme, each user interconnects with any other via shared pairs of entangled photons of different wavelength. In addition, it is possible to improve the information transmission rate above 100 Kbp. / s in the case of high performance detectors, as well as as a high speed control in the modulator used, “they added.

“Of note is the present work, which provides a long-distance point-to-point QSDC connection, combined with QSDC’s recently proposed secure repeater quantum network, which provides secure end-to-end communication across the entire quantum Internet. , will allow the construction of a secure quantum network using current technology, thus realizing the great potential of QSDC in future communications. ”the scientists predict.


Physicists Use Quantum Memory to Demonstrate Secure Quantum Direct Communication


More information:
Zhantong Qi et al, A 15-user quantum secure direct communication network, Light: science and applications (2021). DOI: 10.1038 / s41377-021-00634-2

Provided by Chinese Academy of Sciences

Quote: A 15-user quantum secure direct communication network (2021, September 23) retrieved on September 23, 2021 from https://phys.org/news/2021-09-user-quantum-network.html

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