Quantum networks: prospects and difficulties of implementation
According to estimates of German researchers from the Max Planck Society , the global quantum network will be able to be implemented in the next few years. We will tell you what difficulties there are.
/ Flickr / mike seyfang / cc
A quantum network is a data transmission system that operates according to the laws of quantum mechanics. In such networks, data is exchanged using qubits. These are polarized photons transmitted through the optical communication channel. In order to deploy global quantum networks covering the entire planet, like the Internet, developers and researchers have to solve a number of difficulties. For example, a certain complexity causes the transfer of photons over long distances due to their "fragility." In more detail about this and other problems we will tell further, but first we will talk about why in general to create quantum networks.
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The phenomenon of quantum entanglement binds quantum particles in such a way that when measuring the characteristics of one of them, we automatically recognize the characteristics of the second. Moreover, this connection is maintained even at large distances.
If you establish a connection between two points, you can generate a sequence of random numbers at its two ends. In cryptography, this feature is used to generate encryption keys.
Another advantage of quantum networks is the inability to read broadcast photons twice. The laws of quantum mechanics prohibit the "cloning" of the state of particles of light. When intercepting a qubit, it changes its value. It turns out that when trying to “overhear” the data transmission channel, the attackers will not be able to extract any valuable information. At the exit, they get a random set of numbers.
Thus, quantum networks are almost absolute cryptographic protection. Almost absolute, as scientists from Sweden have proven that it is still possible to “overhear” such a network. To do this, simulate a quantum cipher. Photon detectors ignore unpolarized particles of light, called zeros. If you simulate these zeros at a certain point in time and send them to the receiver, then it will consider the signal to be quantum (although this is not so).
You can solve the problem, but you have to change the principles of the receivers. One of the options is to add a signal strength indicator (since it will change with external intervention). But this will lead to an increase in the cost of developing quantum networks.
The “fragility” of qubits, which makes quantum communication reliable, also brings disadvantages. Single photons change their states or are simply absorbed by the medium due to interference. For this reason, it is difficult to transmit a quantum over a fiber optic cable over a distance of over 100 km.
/ Flickr / Alexandre Delbos / CC
Now fiber optic quantum networks are built using repeaters. They decode the information, encode it again and transmit to other nodes in a chain. However, in this way intermediaries also recognize the content of the message, which can lead to a leak if one of them is compromised. Here a problem arises with the cost - such repeaters use expensive magnets and rare minerals .
It is important to consider the environment in which these networks will be deployed. There is a significant difference between laboratory and “combat” conditions. In the city, temperature changes affect fiber optic cables. This can lead to phase shifts of the photon and cause errors in data transmission.
Quantum teleportation will solve the problem of transmission over long distances. Researchers can optionally introduce two qubits into a state of quantum entanglement. Such a project is being carried out by a group from the Delft Technical University in the Netherlands. Researchers are building a ten-kilometer quantum network between the city of Delft and the Hague.
Such technologies are still in the early stages of development. The fact is that it is difficult to maintain “connectedness” for a long time because of the destructive effect (called decoherence ) that the external environment has on quanta. It is possible to retain the state of quantum entanglement for a fraction of a second.
As we have said, quantum networks are highly resistant to wiretapping. Therefore, they allow you to build reliable distribution systems of cryptographic keys. Such technologies already exist. For example, at the beginning of the year, China launched a cryptographic key distribution system in which data is transmitted via satellites and laser beams. A similar system was proposed by German researchers.
Quantum networks must also integrate quantum computers. It is expected that clusters of quantum machines will accelerate the conduct of physical and chemical simulations, for example, when developing new medical products.
There are use cases outside of science, for example voting. This project was implemented in Switzerland - a few years ago, CERN helped organize a quantum network for elections. According to experts from the Harvard-Smithsonian Center for Astrophysics, in addition to reliability, quantum networks make it possible to implement new strategic voting schemes that are not available today. For example, people will have the opportunity to choose not one candidate, but two at once (the second option).
The development of quantum networks involved in many institutions and organizations. Therefore, more and more similar projects appear lately. About foreign and Russian developments in this area, we will tell in our following materials on Habré.
PS What else do we write in the corporate blog VAS Experts:
PPS Several new articles from our blog on Habré:
/ Flickr / mike seyfang / cc
What are quantum networks?
A quantum network is a data transmission system that operates according to the laws of quantum mechanics. In such networks, data is exchanged using qubits. These are polarized photons transmitted through the optical communication channel. In order to deploy global quantum networks covering the entire planet, like the Internet, developers and researchers have to solve a number of difficulties. For example, a certain complexity causes the transfer of photons over long distances due to their "fragility." In more detail about this and other problems we will tell further, but first we will talk about why in general to create quantum networks.
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How can they be helpful?
The phenomenon of quantum entanglement binds quantum particles in such a way that when measuring the characteristics of one of them, we automatically recognize the characteristics of the second. Moreover, this connection is maintained even at large distances.
If you establish a connection between two points, you can generate a sequence of random numbers at its two ends. In cryptography, this feature is used to generate encryption keys.
Another advantage of quantum networks is the inability to read broadcast photons twice. The laws of quantum mechanics prohibit the "cloning" of the state of particles of light. When intercepting a qubit, it changes its value. It turns out that when trying to “overhear” the data transmission channel, the attackers will not be able to extract any valuable information. At the exit, they get a random set of numbers.
Thus, quantum networks are almost absolute cryptographic protection. Almost absolute, as scientists from Sweden have proven that it is still possible to “overhear” such a network. To do this, simulate a quantum cipher. Photon detectors ignore unpolarized particles of light, called zeros. If you simulate these zeros at a certain point in time and send them to the receiver, then it will consider the signal to be quantum (although this is not so).
You can solve the problem, but you have to change the principles of the receivers. One of the options is to add a signal strength indicator (since it will change with external intervention). But this will lead to an increase in the cost of developing quantum networks.
Why is it difficult
The “fragility” of qubits, which makes quantum communication reliable, also brings disadvantages. Single photons change their states or are simply absorbed by the medium due to interference. For this reason, it is difficult to transmit a quantum over a fiber optic cable over a distance of over 100 km.
/ Flickr / Alexandre Delbos / CC
Now fiber optic quantum networks are built using repeaters. They decode the information, encode it again and transmit to other nodes in a chain. However, in this way intermediaries also recognize the content of the message, which can lead to a leak if one of them is compromised. Here a problem arises with the cost - such repeaters use expensive magnets and rare minerals .
It is important to consider the environment in which these networks will be deployed. There is a significant difference between laboratory and “combat” conditions. In the city, temperature changes affect fiber optic cables. This can lead to phase shifts of the photon and cause errors in data transmission.
Quantum teleportation will solve the problem of transmission over long distances. Researchers can optionally introduce two qubits into a state of quantum entanglement. Such a project is being carried out by a group from the Delft Technical University in the Netherlands. Researchers are building a ten-kilometer quantum network between the city of Delft and the Hague.
Such technologies are still in the early stages of development. The fact is that it is difficult to maintain “connectedness” for a long time because of the destructive effect (called decoherence ) that the external environment has on quanta. It is possible to retain the state of quantum entanglement for a fraction of a second.
Where it will be possible to use quantum networks
As we have said, quantum networks are highly resistant to wiretapping. Therefore, they allow you to build reliable distribution systems of cryptographic keys. Such technologies already exist. For example, at the beginning of the year, China launched a cryptographic key distribution system in which data is transmitted via satellites and laser beams. A similar system was proposed by German researchers.
Quantum networks must also integrate quantum computers. It is expected that clusters of quantum machines will accelerate the conduct of physical and chemical simulations, for example, when developing new medical products.
There are use cases outside of science, for example voting. This project was implemented in Switzerland - a few years ago, CERN helped organize a quantum network for elections. According to experts from the Harvard-Smithsonian Center for Astrophysics, in addition to reliability, quantum networks make it possible to implement new strategic voting schemes that are not available today. For example, people will have the opportunity to choose not one candidate, but two at once (the second option).
The development of quantum networks involved in many institutions and organizations. Therefore, more and more similar projects appear lately. About foreign and Russian developments in this area, we will tell in our following materials on Habré.
PS What else do we write in the corporate blog VAS Experts:
PPS Several new articles from our blog on Habré:
Source: https://habr.com/ru/post/428740/
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