Why should we go to heaven to develop quantum communication? Low Earth Orbit | Satellite | Quantum

Intern journalist Li Zhaoyu

From the power struggles of wise rulers and famous officials in ancient times, to the intricate interplay between great powers in modern times, leakage of information has always been a widely concerned issue in the process of information transmission.

If a communication method can achieve speed, stability, and no loss, then Pompeii will not lose Fazarus, Ma Su will not lose Jieting, and countless events caused by information transmission errors in history will be avoided.

The ancients were unfortunate, but today people are fortunate. The possible means to successfully solve the problem are neither the transmission of information by geese nor the transmission of knowledge by fish, but rather a seemingly mysterious concept - quantum communication.

From June 25 to 27, the Nishan Dialogue on Digital Civilization of the World Internet Conference was held in Shandong. At the achievement exhibition, the "Jinan 1" quantum micro nano satellite launched in 2022 attracted a lot of attention. As quantum communication goes further and further in the field of applications, we cannot help but begin to imagine: what future will quantum communication lead humanity towards? What role does quantum satellites play in it?

Difficulty in eavesdropping on quantum communication

As one of the fundamental concepts of quantum communication, quantum has a high appearance rate in various science fiction works in recent years, but it is not easy to accurately define it.

Liao Shengkai, professor level senior engineer of the Institute of Quantum Information and Quantum Technology Innovation of the Chinese Academy of Sciences, introduced that quantum is an important concept of modern physics, that is, if there is a minimum indivisible basic unit of a physical quantity, it is quantized, and the smallest unit is called quantum.

"The concept of quantum was proposed by German physicist Planck and was first used to explain the energy phenomenon of blackbody radiation." Liao Shengkai said, "Subsequent experiments have shown that other physical quantities such as angular momentum, charge, energy, etc. also exhibit discontinuous quantization phenomena, leading to the emergence of quantum mechanics beyond the framework of Newton's classical mechanics theory."

Liao Shengkai introduced that compared to Newtonian classical mechanics, quantum mechanics has the following characteristics: uncertainty, measurement collapse, and non cloning. These three major characteristics have also become the theoretical basis for the realization of quantum communication.

One of the research topics in quantum communication is quantum key distribution. "Traditional encryption techniques based on computational complexity have the possibility of being cracked in principle, and the difficulty of cracking depends only on the strength of computing power. With the continuous improvement of mathematics and computing power, the possibility of classical passwords being cracked is increasing day by day." Liao Shengkai said, "Unlike classical communication, the security of quantum key distribution is based on basic principles of physics and is independent of computational complexity. Through the transmission of quantum states, users in distant two places share a secure key, and use this key to strictly encrypt information one by one. This is currently the only known communication method that is non eavesdropping and non decipherable, which is unconditionally secure."

Another important aspect of quantum communication is quantum teleportation. Quantum teleportation utilizes quantum entanglement to accurately teleport the unknown quantum state of a particle to a distant location, without the need to teleport the particle itself. Quantum teleportation is a fundamental element in building distributed quantum information processing networks and quantum computers.

Using satellite to transmit information

To do a good job, one must first sharpen their tools. Traditional communication methods such as radio communication require support from relevant equipment such as base stations. Quantum communication, as an advanced means of communication, naturally cannot do without many advanced devices. Since quantum communication typically uses single photons as the physical carrier for information transmission, people cannot help but wonder whether directly connecting a fiber optic is sufficient to meet the needs of long-distance quantum communication?

The answer is obviously negative. The issue of loss has become the crux of the infeasibility of fiber optic methods. "Quantum has the principle of non cloning, so single photon quantum information cannot be amplified like classical communication. Once the transmission distance is far, the problem of loss becomes extremely serious." Liao Shengkai pointed out, "According to data calculations, even with a single photon source and a perfect detector with an emissivity of billions per second, it would take millions of years to transmit a single bit of key through 1200 kilometers of optical fiber, which is clearly unrealistic."

A 1200 kilometer fiber optic cable may still be manufactured, but a single photon source with an emissivity of billions per second and a perfect detector are not within the reach of current technology and other practical conditions, let alone people who cannot wait for millions of years to transmit information. Scientists are forced to search for other directions to solve the problem.

Since the ground is impassable, heaven has become a possible choice. "By utilizing the characteristics of almost vacuum in outer space and very low optical signal loss, the distance of quantum communication can be greatly extended with the assistance of satellites." Liao Shengkai said, "In addition, due to the unique advantage of satellites' convenient coverage of the entire Earth, using satellites for quantum communication is one of the most promising ways to achieve practical quantum communication at ultra long distances on a global scale."

Liao Shengkai introduced that quantum satellites can be divided into three types based on the height of their orbits: low orbit satellites, medium orbit satellites, and high orbit satellites. "These satellites are equipped with some quantum communication devices that can complete certain tasks of quantum communication, so they are called quantum satellites," said Liao Shengkai.

Quantum satellites can also be divided by weight into small satellites, microsatellites, nanosatellites, picoseats, and flying satellites. "Generally speaking, the smaller the satellite, the lower the launch cost, and the higher the cost-effectiveness," said Liao Shengkai.

Liao Shengkai pointed out that an important role of quantum satellites is to serve as relays to extend the distance of quantum communication, thereby achieving long-distance and high difficulty communication. "The ground base station used for quantum communication usually requires several tens of kilometers to be deployed, which is costly and difficult to maintain. If satellite transmission is used to transmit information, all problems will be easily solved," said Liao Shengkai.

A bright future to look forward to

Although quantum satellites are very powerful, relying solely on one quantum satellite is clearly not enough to truly support wide area quantum communication. More quantum satellites need to unite and collaborate to form a satellite network.

Liao Shengkai introduced that generally speaking, there are two types of solutions to achieve satellite networking. One type relies on a large number of low orbit satellites to form a real-time coverage network. The Iridium program, Star Chain program, and others all belong to this category. "The communication time for low orbit satellites to pass through ground stations is often only a few minutes, so it requires hundreds or even tens of thousands of satellites," said Liao Shengkai.

The other type mainly relies on medium to high orbit satellites, such as geostationary orbit satellites that are relatively stationary on the ground. "The geostationary orbit is approximately 36000 kilometers high, which is the current orbit of broadcasting and television satellites and conventional communication satellites." Liao Shengkai said, "Generally speaking, three geostationary orbit satellites can achieve global coverage."

Liao Shengkai introduced that generally speaking, low orbit satellites have low orbits, strong signals, and high transmission rates, but their transit time is short and the amount of information transmitted is small; High orbit satellites have high orbits, weak signals, and low transmission rates, but they have long transmission times and can work almost all day, transmitting a large amount of information; Medium orbit satellites are located between high orbit satellites and low orbit satellites, with both characteristics.

"The specific form of satellite should be chosen according to the needs. In a quantum network established using satellites, it is often necessary to comprehensively utilize three types of satellites," said Liao Shengkai. With the support of quantum satellites, quantum communication has made great progress. But in Liao Shengkai's view, in order to truly achieve large-scale applications, it is necessary to continue efforts in both policy and technology.

From a technical perspective, quantum communication should also develop towards increasing bit rate, increasing distance, and reducing costs. "At present, the coding rate of mature quantum communication products is still relatively low, usually only reaching the level of thousands of bits per second. It needs to be combined with symmetric cryptographic algorithms to achieve big data rate encryption protection. On the other hand, the cost of mature products is high, which is not conducive to large-scale promotion and application." Liao Shengkai introduced.

From a policy perspective, as a way of key distribution or key negotiation in cryptography, quantum communication needs to meet the compliance of cryptographic applications and establish industry standards before it can be widely applied and promoted. "Although some standards have been initially formed and released domestically and internationally through nearly a decade of efforts, more support is needed to form a complete system and improve evaluation and certification capabilities in order to support large-scale applications," said Liao Shengkai.

Despite facing some challenges, the future that quantum communication can bring is undoubtedly extremely desirable. "Imagine that in the future, everyone's privacy can be effectively protected, and it will be easy to transmit messages without damage for millions of miles." Liao Shengkai said, "I always believe that quantum communication will lead humanity towards a better future!"

Intern journalist Li Zhaoyu

From the power struggles of wise rulers and famous officials in ancient times, to the intricate interplay between great powers in modern times, leakage of information has always been a widely concerned issue in the process of information transmission.

If a communication method can achieve speed, stability, and no loss, then Pompeii will not lose Fazarus, Ma Su will not lose Jieting, and countless events caused by information transmission errors in history will be avoided.

The ancients were unfortunate, but today people are fortunate. The possible means to successfully solve the problem are neither the transmission of information by geese nor the transmission of knowledge by fish, but rather a seemingly mysterious concept - quantum communication.

From June 25 to 27, the Nishan Dialogue on Digital Civilization of the World Internet Conference was held in Shandong. At the achievement exhibition, the "Jinan 1" quantum micro nano satellite launched in 2022 attracted a lot of attention. As quantum communication goes further and further in the field of applications, we cannot help but begin to imagine: what future will quantum communication lead humanity towards? What role does quantum satellites play in it?

Difficulty in eavesdropping on quantum communication

As one of the fundamental concepts of quantum communication, quantum has a high appearance rate in various science fiction works in recent years, but it is not easy to accurately define it.

Liao Shengkai, professor level senior engineer of the Institute of Quantum Information and Quantum Technology Innovation of the Chinese Academy of Sciences, introduced that quantum is an important concept of modern physics, that is, if there is a minimum indivisible basic unit of a physical quantity, it is quantized, and the smallest unit is called quantum.

"The concept of quantum was proposed by German physicist Planck and was first used to explain the energy phenomenon of blackbody radiation." Liao Shengkai said, "Subsequent experiments have shown that other physical quantities such as angular momentum, charge, energy, etc. also exhibit discontinuous quantization phenomena, leading to the emergence of quantum mechanics beyond the framework of Newton's classical mechanics theory."

Liao Shengkai introduced that compared to Newtonian classical mechanics, quantum mechanics has the following characteristics: uncertainty, measurement collapse, and non cloning. These three major characteristics have also become the theoretical basis for the realization of quantum communication.

One of the research topics in quantum communication is quantum key distribution. "Traditional encryption techniques based on computational complexity have the possibility of being cracked in principle, and the difficulty of cracking depends only on the strength of computing power. With the continuous improvement of mathematics and computing power, the possibility of classical passwords being cracked is increasing day by day." Liao Shengkai said, "Unlike classical communication, the security of quantum key distribution is based on basic principles of physics and is independent of computational complexity. Through the transmission of quantum states, users in distant two places share a secure key, and use this key to strictly encrypt information one by one. This is currently the only known communication method that is non eavesdropping and non decipherable, which is unconditionally secure."

Another important aspect of quantum communication is quantum teleportation. Quantum teleportation utilizes quantum entanglement to accurately teleport the unknown quantum state of a particle to a distant location, without the need to teleport the particle itself. Quantum teleportation is a fundamental element in building distributed quantum information processing networks and quantum computers.

Using satellite to transmit information

To do a good job, one must first sharpen their tools. Traditional communication methods such as radio communication require support from relevant equipment such as base stations. Quantum communication, as an advanced means of communication, naturally cannot do without many advanced devices. Since quantum communication typically uses single photons as the physical carrier for information transmission, people cannot help but wonder whether directly connecting a fiber optic is sufficient to meet the needs of long-distance quantum communication?

The answer is obviously negative. The issue of loss has become the crux of the infeasibility of fiber optic methods. "Quantum has the principle of non cloning, so single photon quantum information cannot be amplified like classical communication. Once the transmission distance is far, the problem of loss becomes extremely serious." Liao Shengkai pointed out, "According to data calculations, even with a single photon source and a perfect detector with an emissivity of billions per second, it would take millions of years to transmit a single bit of key through 1200 kilometers of optical fiber, which is clearly unrealistic."

A 1200 kilometer fiber optic cable may still be manufactured, but a single photon source with an emissivity of billions per second and a perfect detector are not within the reach of current technology and other practical conditions, let alone people who cannot wait for millions of years to transmit information. Scientists are forced to search for other directions to solve the problem.

Since the ground is impassable, heaven has become a possible choice. "By utilizing the characteristics of almost vacuum in outer space and very low optical signal loss, the distance of quantum communication can be greatly extended with the assistance of satellites." Liao Shengkai said, "In addition, due to the unique advantage of satellites' convenient coverage of the entire Earth, using satellites for quantum communication is one of the most promising ways to achieve practical quantum communication at ultra long distances on a global scale."

Liao Shengkai introduced that quantum satellites can be divided into three types based on the height of their orbits: low orbit satellites, medium orbit satellites, and high orbit satellites. "These satellites are equipped with some quantum communication devices that can complete certain tasks of quantum communication, so they are called quantum satellites," said Liao Shengkai.

Quantum satellites can also be divided by weight into small satellites, microsatellites, nanosatellites, picoseats, and flying satellites. "Generally speaking, the smaller the satellite, the lower the launch cost, and the higher the cost-effectiveness," said Liao Shengkai.

Liao Shengkai pointed out that an important role of quantum satellites is to serve as relays to extend the distance of quantum communication, thereby achieving long-distance and high difficulty communication. "The ground base station used for quantum communication usually requires several tens of kilometers to be deployed, which is costly and difficult to maintain. If satellite transmission is used to transmit information, all problems will be easily solved," said Liao Shengkai.

A bright future to look forward to

Although quantum satellites are very powerful, relying solely on one quantum satellite is clearly not enough to truly support wide area quantum communication. More quantum satellites need to unite and collaborate to form a satellite network.

Liao Shengkai introduced that generally speaking, there are two types of solutions to achieve satellite networking. One type relies on a large number of low orbit satellites to form a real-time coverage network. The Iridium program, Star Chain program, and others all belong to this category. "The communication time for low orbit satellites to pass through ground stations is often only a few minutes, so it requires hundreds or even tens of thousands of satellites," said Liao Shengkai.

The other type mainly relies on medium to high orbit satellites, such as geostationary orbit satellites that are relatively stationary on the ground. "The geostationary orbit is approximately 36000 kilometers high, which is the current orbit of broadcasting and television satellites and conventional communication satellites." Liao Shengkai said, "Generally speaking, three geostationary orbit satellites can achieve global coverage."

Liao Shengkai introduced that generally speaking, low orbit satellites have low orbits, strong signals, and high transmission rates, but their transit time is short and the amount of information transmitted is small; High orbit satellites have high orbits, weak signals, and low transmission rates, but they have long transmission times and can work almost all day, transmitting a large amount of information; Medium orbit satellites are located between high orbit satellites and low orbit satellites, with both characteristics.

"The specific form of satellite should be chosen according to the needs. In a quantum network established using satellites, it is often necessary to comprehensively utilize three types of satellites," said Liao Shengkai. With the support of quantum satellites, quantum communication has made great progress. But in Liao Shengkai's view, in order to truly achieve large-scale applications, it is necessary to continue efforts in both policy and technology.

From a technical perspective, quantum communication should also develop towards increasing bit rate, increasing distance, and reducing costs. "At present, the coding rate of mature quantum communication products is still relatively low, usually only reaching the level of thousands of bits per second. It needs to be combined with symmetric cryptographic algorithms to achieve big data rate encryption protection. On the other hand, the cost of mature products is high, which is not conducive to large-scale promotion and application." Liao Shengkai introduced.

From a policy perspective, as a way of key distribution or key negotiation in cryptography, quantum communication needs to meet the compliance of cryptographic applications and establish industry standards before it can be widely applied and promoted. "Although some standards have been initially formed and released domestically and internationally through nearly a decade of efforts, more support is needed to form a complete system and improve evaluation and certification capabilities in order to support large-scale applications," said Liao Shengkai.

Despite facing some challenges, the future that quantum communication can bring is undoubtedly extremely desirable. "Imagine that in the future, everyone's privacy can be effectively protected, and it will be easy to transmit messages without damage for millions of miles." Liao Shengkai said, "I always believe that quantum communication will lead humanity towards a better future!"