Rebirth 1999: Opening the Age of Black Technology

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Quantum communication literally means the application of quantum science in communication.

This topic is very complicated. It takes a semester to talk about quantum and communication separately. It can only be explained simply with an inaccurate metaphor, because an accurate explanation requires deduction of mathematical publicity. The popular science that can be seen now is all comparative. Accurate science is just popular science and cannot be regarded as a standard.

Quantum communication is divided into two types according to whether the information transmitted is classical or quantum.

The former is used for the transmission of quantum keys, which has not yet left the scope of optical fibers.

The latter is used in the distribution of quantum teleportation and quantum entanglement.

Teleportation is the highest pursuit of quantum science. Simply put, it is to copy a thing (information) 100% and then send it to the receiving place. Exactly the same copy, but this is absolutely impossible, because quantum mechanics has uncertainty and does not allow accurate copying of information.

This feature that cannot be completely replicated is called "God really casts dice", and Bohr beat Einstein on this point, absolutely fierce.

If it is a written expression, it is generally described by Bell's inequality and the uncertainty principle.

Then based on this feature, quantum communication came into being. At present, the most important thing is to greatly improve the security. As for the teleportation based on quantum entanglement, it is also planned!

So why is quantum communication so secure?

We have to start from the beginning. Matter is composed of atoms, and the energy of atoms does not change continuously. It is done piece by piece, and the smallest bit is called a quantum.

When we use quantum communication satellites to send codes, we must first send polarized photons, representing a bit 1 or 0.

Since light is an electromagnetic wave, it has wave-particle duality, so that light can be subdivided into photons, and at the same time it is very unstable and can be polarized in an unspecified direction. At this time, we have to specify the polarization angle in advance, such as towards zero angle The polarized one represents 0, and the one polarized towards 90 degrees represents a bit 1.

Then the receiving device can only allow polarized photons with zero angle and 90 degrees to pass through, and even the receiving device must set a fixed angle in advance, such as 45 degrees, so that the correct bit can be received smoothly, and polarized photons with other angles are wrong. is filtered.

But what if the photon with zero angle wants to pass through the 0-bit hole and the 1-bit hole?

Then you have to roll the dice. This is the so-called "God rolls the dice".

In this way, when the photons sent by the communication satellite and the receiver are placed in the same direction, the received bits are correct. Interestingly, the receiver's placement angle is also random. Every time we have to discuss the issue of placement angle

If both are random, a lot of unsuccessfully transmitted bits will be generated, the unsuccessful bits will be deleted, and the rest will be the random password sent this time.

Since only one photon is sent at a time, if someone eavesdrops, it means that the information is intercepted and read, and the receiver will definitely know it, because it has been said before.

It is impossible to have the concept of complete duplication in quantum, and it is impossible to give the same photon information after stopping it. This is the "quantum non-cloning theorem" and the uncertainty principle at work, and it truly achieves one-time encryption. .

It is randomly generated, cannot be eavesdropped, and cannot be cracked, so the security of quantum communication is naturally high. The current method of transmitting passwords in quantum communication is called the BB84 protocol.

At present, the quantum distribution on hand of human beings does not communicate, but only distributes keys! Only assign keys!

Quantum key distribution cannot actively protect against eavesdropping, but can only passively detect whether others eavesdrop on themselves.

The detection of eavesdropping is still based on the principles of uncertainty and non-cloning, which is the current status of human beings.

The current quantum key still relies on conventional communication and cannot exceed the speed of light. The quantum entanglement that exceeds the speed of light is just an illusion. It is impossible to know whether the cat is dead or alive without opening the box! Quantum teleportation is too magical, and perfect quantum entanglement applications should be unattainable.

At present, quantum keys are still commercialized. The longest distance of quantum key distribution in the laboratory state is 260 to 300 kilometers. The realization of long-distance quantum communication depends on relay stations. Relays are divided into quantum relays and trusted relays. The latter has been industrialized at present, and the principle is that A transmits information to B, and B then transmits it to C, and the key is landed halfway, which has certain risks.

The quantum relay is not grounded. The quantum entanglement distribution technology is used to establish shared entangled pairs between adjacent sites, and the quantum storage technology is used to store the entangled pairs, and then the long-distance free space transmission technology is used to realize the quantum entanglement conversion. The fidelity is extremely high. high.

The longest distance of the best quantum teleportation principle experiment at present is 143 kilometers, provided that the environment in the Canary Islands of Spain is good. It looks much better than the 16 kilometers in the capital of the Xia Kingdom and the 97 kilometers in the atmosphere of the QH province.

However, there are too many doubts in Spain's experiment. No matter how you look at it, it looks like a scam to break Xia Guo's record in a fit of anger.

If you want to reach a longer distance, you have to avoid atmospheric interference with the fragile quantum state of photons, and you have to use satellites to distribute photons. The conversion of thousands of kilometers in space to the ground is only about 8 kilometers. It is imperative to go into space.

Xia Guo’s achievements are the strongest, but only achieved the realization of six-photon entanglement, eight-photon entanglement and ten-bit super-entanglement. Even if the transmission of 100 kilometers on the ground is achieved, it is only theoretically possible to transmit 1,000 kilometers in space. It's still far away.

The system has given guidelines, but the current manufacturing level is still lacking, and the improvement cannot be achieved in one step.

Chen Xiao is not greedy at all, he decided to start with the relay station first, turn the trusted relay into a quantum relay, and then slowly turn the quantum key into quantum state teleportation, although it will definitely not reach 100%, but The reliability of this thing is really strong, as long as it is close to perfect quantum entanglement, many things can be omitted.

The idea is not without, it is only necessary to divide the original information into two parts, classical information and quantum information, and transmit them to the receiver through their respective channels.

After receiving it, it can be copied. It is worth noting that the classical information is obtained by the sender through some measurement of the original matter, and the quantum information is the rest of the information that the sender did not extract during the measurement.

What is transmitted in this process is only the quantum state of the original matter, not the original matter itself.

The sender may not even know anything about this quantum state, while the receiver puts other particles in the quantum state of the original matter.

In this scheme, the nonlocality of entangled states plays an extremely important role.

Chen Xiao didn't want to transfer items directly in one step, but just communicated. It didn't need to be so perfect, so the difficulty was naturally reduced a lot.

At that time, communication based on quantum entanglement will be quantum communication in the true sense. Now it can only be called quantum encryption communication, which is not a concept at all.

If the construction of quantum communication is really completed, there is no need to worry about the signal problem. The equipment is equipped with a quantum communication chip. You only need to use the principle of quantum entanglement to see the quantum state here, and you can understand the information transmitted by the other party.

The experiment was handed over to Changtian Academy of Natural Sciences to design and host, and it has been involved in it before.

To be on the safe side, Chen Xiao still invited relevant bigwigs from Xiaguo Academy of Sciences to discuss, including Pan Wei and Lu Yang, two top experts.

To be honest, their team is very strong, and it is their credit that Xia Guo is ahead of the world. When they were first invited, they didn't pay much attention to it. How could Changtian Technology be involved in this aspect?

But after thinking about it, it may not be impossible for Changtian Technology to even produce creatures with controllable nuclear fusion and automatic evolution, so there are still some small expectations.

When the symposium started, Pan Wei and Lu Yang knew they were wrong, and the progress of Changtian Technology was similar to that of Xia Guo Academy of Sciences.

"The distance between you has exceeded two hundred kilometers?"

"Has the quantum random generator reached 20Gbps? This is already a little ahead of us! It's a pity that it still can't be truly random."

"You also have a 6-photon spin-orbit angular momentum experimental platform? Can the spin and orbital angular momentum be transmitted at the same time? You have also done experiments with 8-photon, 10-bit super-entanglement,"

"You also use the cold atom quantum storage technology to surpass the quantum exchange of storage and reading functions! You can play the length of 350 meters of optical fiber! This is the quantum repeater that is urgently needed for long-distance quantum communication clocks, but This distance is still too short."

Pan Wei and Lu Yang no longer underestimated them. Changtian Technology has already achieved this step without saying a word. Doesn't Changtian Technology have any blind spots in scientific research? Any cutting-edge field has been involved and has made great achievements.

A few years ago, when Changtian Technology completed the 4G communication layout, it was experimenting with quantum technology, but there was no publicity because it had no application.

"We were greatly moved by your candid announcement. To be honest, we don't have any outstanding results here. I'm ashamed!" Pan Wei told the truth.

Guo Can is the person in charge of the Changtian Science and Technology Quantum Project.

This person is about the same age as Pan Wei, and they are both young and promising people. He said humbly: "Academician Pan has won the award. If you have results that can be announced, it means that there are more things that have not been revealed."

"Those are all speculations, they are all experiments, and they haven't succeeded yet..."

"Don't be too self-effacing. At this point, conjectures are often more valuable than actual achievements. Maybe a conjecture is confirmed, and the previous achievements are not worth mentioning. We invite you to come here to show our Ideas, discuss with everyone, inspire each other, and achieve theoretical breakthroughs earlier." Guo Can waved his hand.

"Well, if you have any ideas, let's see if it works." Lu Yang is much more straightforward. He himself came here for research, and worldly wisdom is not important at all.

"..."

Guo Can was stunned for a moment, and then distributed the research idea. If Pan Wei and Lu Yang can't understand it, no one on this planet can understand it.

When Guo Can got the information given by Chen Xiao, he was completely stunned. He seemed to understand these things, but where did the boss get them?

If you don't fully understand it yourself, how can you transform it into a newer result?

So he was full of anticipation for the arrival of Pan Wei and Lu Yang, just like a person who is not sure about a problem, but two people with similar levels happened to come, so they have to show them whether they are good or bad.

After a while, Pan Wei and Lu Yang frowned and didn't say a word for a long time.

"How is it? Tell me something. Are the principles and experimental schemes all right?" Guo Can was worried.

"I don't fully understand it." Academician Lu Yang replied very bachelorly.

Academician Pan Wei also shook his head: "I see it in a cloud, and I always feel that the designed experiment is okay. If it were me, I would design it like this. The most critical question is, where do the principles and ideas come from? Span It's a bit big, but it seems to make sense."

Hearing this, Guo Can's heart fell to the ground. It turned out that it wasn't that he was unsure, but everyone was unsure! Since you are not sure, what are you afraid of when you start an experiment? No one has a standard answer, so find the answer yourself.

"The principle and idea came to me by accident. This is based on intuition, so I asked two academicians to come over for reference." Guo Can did not say that it was the information given by Chen Xiao. The sources of these things are basically kept secret. Chen Xiao Don't want to draw too much attention.

"It's a trick, anyway, we don't have any ideas." Lu Yang is very frank, researching to the most advanced level means building a new way by himself, without the predecessors as a reference.

Pan Wei also meant the same thing. Although the research subdivisions of the two are different~www.readwn.com~ but the foundation is the application of quantum, if Lu Yang has problems, he will naturally have problems.

The experiment was carried out very quickly, and it was really a race against time.

The specific experimental idea of ​​Changtian Technology is to use a super-strong laser as a light source, which has the advantage of being more stable than a weakly correlated light source, and the quantum state is not easy to change.

The disadvantage is that once the laser is fired, the photons do not collapse one by one. In this case, the problem of carrying information on the photons has to be solved.

The security of quantum communication is that one photon is equal to one code. If such a bunch of photons all contain information, they are theoretically easy to be intercepted and then cracked.

In this way, it is necessary to ensure that a single photon is sufficiently powerful. What Changtian Technology has to do is to capture specific photons, as for other photons in the beam, they are equivalent to the fuel when the rocket is launched, and play a role in propulsion.

A beam of light captures specific photons for encryption. After receiving the laser light, the receiving device will perform multi-slit interference on the beam to separate the photons, and then pass through the polarization equipment to obtain specific photons. The process is complicated, but it is all done at the speed of light. The difficulty can be imagined.

"The quantum state generator is stable and continuously enhanced. Turn on the ultra-high voltage power supply device to ensure that the laser is powerful enough!"

"In the construction of the quantum channel, it has been relatively stable, but the distance is too short."

"Nonsense, if the distance is not short, we would have achieved quantum communication a long time ago!"

"Where's the quantum testing device? Is it on?"

"opened!"

"What about the device that records specific photon information? This is the password!"

"opened!"

"Then let's get started!"

Everyone is very nervous. Although many experiments are needed to change the frequency and polarization angle, whether the idea can be realized or not, everyone hopes that it can be done once.

(end of this chapter)

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