This article is from WeChat official account:Fyvoice (ID: fyvoice) , author: Yuanlan Feng, editor: Chen Xin Yue, the original title: “4600 kilometers across, the world’s leading quantum communication China, Europe and how long to catch up? | Yuan Lanfeng”, title picture from: Visual China
Recently, many media reported that in the early morning of January 7, 2021, the University of Science and Technology of China announced the establishment of a “space-to-earth integrated quantum communication network spanning 4,600 kilometers.”
The University of Science and Technology of China announced in the early morning that my country has built the world’s first satellite-to-earth quantum communication network https://cm163.com/news/a/FVNP5ELC04079BLH.html p>
When most people see this news, their first reaction may be: Why did you announce it in the early morning? What is so urgent? The second reaction may be: What does it mean to connect such a long string of tall words?
Actually, this is not an emergency at all. The so-called early morning announcement was only because the paper was published in the top international journal Nature in the early morning of January 7.
Report on the homepage of the University of Science and Technology of China: The University of Science and Technology of China has successfully verified the feasibility of building an integrated world-to-earth quantum communication network (http://news.ustc.edu.cn/ info/1055/73813.htm)
“Nature” is a British journal. It has a time difference with China, so it will be online in the early morning.
“Nature” thesis “A quantum communication network spanning 4600 kilometers” (https://www.nature.com/articles/s41586-020 -03093-8)
The really interesting thing is this paper. I have interpreted many scientific papers, most of which are the latest research results and need to be released in time. But this is not, it is a summary of the work of the past few years. A result that doesn’t need to rush for time, is promoted by the media as if one hundred thousand rushes, it is really very entertaining.
Get back to business. In terms of science and engineering, this achievement is very important, and it is equivalent to a final word: The conditions for wide-area quantum secure communication technology in practical applications have initially matured, laying the foundation for science and technology for a quantum secure communication network covering the world in the future basis. In this field, China is far ahead of other countries.
Most people may not understand what quantum secure communication is. Let me introduce it briefly.
Since ancient times, people have proposed many cryptosystems. But none of them could guarantee security in principle until the advent of quantum secure communication.
This is because traditional passwords always require a messenger to send the password book. “Red Lantern”, “Latent” and other spy warfare film agents are doing this, the professional name of the codebookIt is called a key. If the messenger is caught or defected, the loss will be huge.
“Red Lantern”
Later, cryptographers invented a clever method that does not require people to send the key, but uses mathematical puzzles to encrypt. Stealing secrets has become a kind of math challenge. If you can solve this math puzzle, you can steal secrets. But cryptographers believe that this problem is very difficult, and you can’t solve it in normal time, so it can be kept secret.
Public key cryptosystems (such as RSA) use mathematical problems (such as factorization) as the basis for confidentiality
However, the disadvantages of this method are also obvious. How do you know that the enemy cannot crack it? If he cracks it, will he tell you?
In fact, many passwords considered unbreakable in history have been cracked. A classic example is the story of the Allied forces cracking the German cryptographic system (Enigma) during World War II.
Guderian, the founder of Blitzkrieg, is on the command vehicle, and the Enigma cryptographic machine is on the lower left.
The father of computer science and the famous mathematician Alan Turing(Alan Mathison Turing, 1912~1954) participated in this Work played an important role. The British government estimates that solving the mystery has advanced the end of World War II by two years. In order to keep the Germans in the dark, the Allies sometimes even deliberately sent some troops to death. So until the defeat, Germany did not find that its password was cracked.
Alan Turing
Therefore, the previous passwords are always in such a dilemma, either the messenger may be caught, or the math may be cracked. Quantum secure communication is a unique approach, and proposes a secure method that neither requires messenger nor depends on mathematical problems.
Due to space limitations, I cannot introduce the specific process of quantum secure communication here. I can only tell everyone that this is a very high-tech approach, and you must understand quantum mechanics if you want to understand it.
Some people hope to describe it in some kind of brain teaser, and invent all kinds of simple terms. I can only say that these statements are all wrong, and this is by no means a brain teaser to describe. To understand how quantum secure communication is done, you have to read professional textbooks, or read my articles to understand it.(“You can fully understand quantum information (14) | Yuan Lanfeng”).
The professional name of quantum secure communication: Quantum Key Distribution
However, I can tell you the principles and effects of quantum secure communication.
First of all, there is a basic physics theory called quantum mechanics(“Let the central group learn What is the quantum technology of China? I have done this science popularization for five years (1) What is quantum | Yuan Lanfeng”). It is one of the two pillars of physics today, and the other is the theory of relativity. Quantum mechanics is the essential description of the microscopic world.
Next, there are some features in quantum mechanics that can be used by information science. There are three main points: superposition, measurement and entanglement. I call them the “three great meanings” ( “What is the quantum technology that allows the central What? I have done this science popularization for five years (2) The Three Profound Meanings of Quantum Mechanics | Yuan Lanfeng”).
The method of quantum secure communication is to use these characteristics of quantum mechanics to allow the sender and receiver of information to directly establish contact. The two sides passed a seriesList the operations of quantum mechanics(In practice, it is to transmit and receive a series of single photons, and randomly select “basic set” and other professional content) , And at the same time obtained a random string, like 011011100011.
The most important thing is that the random strings in both hands are exactly the same, which is guaranteed by the principles of quantum mechanics. Moreover, the enemy cannot steal secrets. Once someone is eavesdropping, both parties will find out immediately. This is also guaranteed by the principles of quantum mechanics.
In this way, both parties can use the random string in their hands as the key. Use this key to encrypt the information, and the subsequent transmission is completely traditional communication. For example, you can use optical fiber, you can use the phone, you can use e-mail, or even ordinary mail.
This is because after the key is securely obtained, the ciphertext can be guaranteed not to be mathematically cracked. Therefore, the technical difficulty of quantum secure communication lies in the generation of the key, and this step requires a quantum channel. The latter ciphertext transmission is very simple, this step can be any traditional channel.
You may want to ask: Why not directly use quantum channels to transmit information? The answer is that this set of quantum mechanics operations can only generate random strings, and cannot represent information as you wish. But a random string is just right as a key, so it can’t be used as a method to directly transmit information, but it has become the safest way to encrypt information.
The principle of quantum secure communication was proposed by scientists in Canada and the United States in 1984. But since the 21st century, at the experimental level, China has come from behind.
In 2016, China launched the world’s first quantum science experimental satellite “Mozi”.
On August 16, 2016, the “Mozi” quantum satellite was launched
In 2017, China opened the world’s first quantum secure communication trunk line “Beijing-Shanghai trunk line”(“Interpretation of the Beijing-Shanghai trunk line of quantum communication, including your understanding | Yuan Lanfeng”).
At the press conference for the opening of the Beijing-Shanghai trunk line on September 29, 2017, Bai Chunli, President of the Chinese Academy of Sciences (on the right side of the electronic screen) passed on the spot The “Micius” quantum science experimental satellite, conducted the world’s first intercontinental quantum secure communication video call with the Dean of the Austrian Academy of Sciences Anton Salinger (on the left of the electronic screen)
The Micius has realized the quantum secret communication between the satellite and the ground station. The transmission medium is vacuum and atmosphere, which is called free space transmission. The Beijing-Shanghai trunk line realizes 2,000 kilometers of quantum secure communication between Beijing and Shanghai, and the transmission medium is optical fiber. The two methods have their own advantages and can be used complementary.
32 nodes of the Beijing-Shanghai trunk line
This recent article by Pan Jianwei and others introduced the results of the operation of the Mozi and Beijing-Shanghai trunk line so far. The Beijing-Shanghai trunk line has 32 nodes,There are also two ground stations that can be connected to the Beijing-Shanghai trunk line through the Mozi, one in Xinglong, Hebei and the other in Nanshan, Xinjiang. Therefore, the total span reached 4,600 kilometers.
“Nature” paper picture 1: Schematic diagram of the world-earth integrated quantum communication network
Whether it is in terms of the number of connections, the rate of key generation, the ability to resist physical attacks, or the stability, etc., this 4,600-kilometer world-earth integrated quantum secure communication network has The outstanding performance initially met the practical requirements. The paper gives a lot of data, everyone is welcome to read it.
“Nature” Paper Table 1: The backbone network of the world-earth integrated quantum communication network, four metropolitan area networks (Beijing, Jinan, Hefei, Shanghai), Two ground stations (Xinglong, Nanshan) and various indicators of the Mozi satellite (number of relays, number of nodes, number of users, number of connections, average length, loss rate, bit rate)
In the future, based on the world-earth integrated quantum communication network, China will further promote the wide application of quantum communication in the fields of finance, government affairs, national defense, and information. An example is the national ground-based timing network using quantum precision measurement methods, which will become the world’s largest and most accurate optical fiber timing system.
In terms of basic research, the world-earth integrated quantum communication network will also become an importantInfrastructure. For example, experiments on ultra-large-scale quantum interference can explore the fusion of quantum mechanics and general relativity, which is the most basic problem of today’s physics.
Finally, let’s introduce the situation in other countries. It is often said that quantum communication is fake because other countries do not engage in it. This statement is logically wrong, because the standard for judging true or false should not be something that other countries cannot do. And at the factual level, this statement is also wrong.
Europe and the United States have a lot of plans and research in quantum communication. They all want to do what China does, but they have not done it yet.
For example, Germany and Japan have plans to launch quantum communication satellites. Germany has not yet released it. Japan released a satellite called “Socrates” in 2017, which claims to have achieved quantum communication. But if you look at their papers, you will find that they are only testing quantum communication-related technologies and have not yet implemented quantum communication(“Has Japan really successfully conducted experiments on ultra-small satellite quantum communications? | Yuan Lanfeng”). Because their technical level is not enough, they need to send 100 million photons at a time to receive them, but quantum communication must send only one photon at a time, so Japan is far from reaching the standard.
Japan’s miniature communication satellite “Socrates” (from the homepage of the Japan Institute of Information and Communication Research)
In 2020, the “Quantum Network Strategic Vision” released by the United States proposed: “In the next five years, the United States will demonstrate the basic science and key technologies for realizing quantum networks, from quantum interconnections, quantum repeaters, quantum memories to High-throughput quantum channels, and intercontinental space-based entanglement distribution.”
In 2020, the EU’s Quantum Flagship Program “War”Strategic Research Agenda” puts forward: “The 3-year vision is to use the QKD protocol and a network with trusted relay nodes to achieve global secure key distribution, and the 6-10 year vision is to use quantum repeaters to achieve more than 800 kilometers on optical fibers. Quantum communication.”
Compared with these plans, we can see how advanced China is. China leads the European Union by 3 to 5 years and the United States by 5 to 8 years.
About the author: Yuan Lanfeng, Ph.D. in Chemistry, University of Science and Technology of China, Associate Researcher, Hefei National Research Center for Microscale Material Science, University of Science and Technology of China, Society of Science and Technology and Strategy Chairman, speaker of the program “Science and Technology Yuanren”, standing committee member of Anhui Science and Technology Association, standing committee member of China Youth New Media Association, committee member of China Science Writers Association, selected as one of the top ten science communication figures of “Dianzan·2018 Popular Science China”, Wei Bo@中科大胡不归, know almost @袁岚峰.
This article is from WeChat official account:Fyvoice (ID: fyvoice), author: Yuanlan Feng, editor: Chen Xin Yue