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Main text Chapter 1005 Heavy technology upgrade

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    Chapter 1005 Heavy technology upgrade

    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 transmitted information 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 for 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, generally use Bell's inequality, uncertainty principle, etc. to describe.

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

    So why is quantum communication so safe?

    Things have to be said from the beginning. Matter is composed of atoms, and the energy of atoms does not change continuously. It is done one by one, and the smallest amount is called a quantum.

    ? When we use a quantum communication satellite to send a password, we must first send a polarized photon, representing a bit 1 or

    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  Polarized represents 0, and polarized towards 90 degrees represents bits

    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 emitted 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, there will be a lot of unsuccessfully transmitted bits, delete the unsuccessful bits, and the rest is the random password sent this time.

    Since only one photon is sent at a time, if it is eavesdropped, 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.  .

    Generated randomly, cannot be eavesdropped, and cannot be cracked, the security of quantum communication is naturally high. The current routine of quantum communication transmission code is called 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 are eavesdropping 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. That kind of quantum entanglement at 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 entanglement 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.

    ?These are all speculations, they are all experimenting, 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 sophistication 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 confused. He seemed to understand these things, but where did the boss get them?

    If you don't fully understand it yourself, how can it be transformed 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 solving a problem, but two people with similar levels happened to come, and he had to show them whether they were 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 very anxious.

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

    Academician Pan Wei also shook his head: "I am confused, and I always feel that the designed experiment is okay. If it were me, I would also design it like this. The most critical question is, where did the principle and idea 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 was not that he was not sure, but everyone was not sure!  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.

    "There is something to do, we don't have any ideas anyway." Lu Yang is very frank, researching to the most advanced level means building a new way by himself, without the reference of his predecessors.

    Pan Wei also meant the same thing. Although the research subdivisions of the two are different, they are based on 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 super-strong laser as the light source, which has the advantage of being more stable than weakly correlated light sources, 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 lies in the fact that one photon is equal to one password. If such a bunch of photons all contain information, it is theoretically easy to be intercepted and then cracked.

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

    Capture specific photons in a beam of light 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 is the quantum test 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 required to change the frequency and polarization angle, whether the idea can be realized or not, everyone hopes that it can be done once.
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