What is the use of quantum communication that cannot directly transmit information? The most basic logic is that no matter how far apart they are, measuring one of them can instantly determine the other. Logically speaking, we can take a pair of entangled photons and show upward polarization and downward polarization. Correspondingly converted to "0" and "1"
and a large string of characters composed of "0" and "1" can represent any information. Doesn't this allow super long distances, can be transmitted at super-light speed Got the information? For example, two entangled photons are very far apart, but if the polarization measured from one side is upward, for example, it represents "0", then you know that the polarization on the other side is downward, which represents "1". can also be understood as ultra-long distance. Send a message to the other side at the speed of light "1"
➡️ The process of "error correction" in quantum communication
But the key problem is that "quantum superposition state" is completely random, and fundamentally it is impossible to decide what to send to the other side. What is sent is "0" or "1". If "0011" is sent, it represents a message, and the result is randomly displayed, for example, 010011...
, which is equivalent to the other side receiving a bunch of garbled codes, no To represent any information, I can only tell the other side to pick out , 4, 6, 7 based on the observed random results.
Then as soon as the other side is adjusted, clear and accurate information is displayed, However, this error correction process still requires traditional information channels to communicate whether it is making a phone call or sending an email, so the whole process still cannot exceed the speed of light.
➡️ Quantum communication cannot directly transmit information or cannot be separated from traditional information channels, so is this unnecessary?
It is better to just call and tell the other side what the information is. Quantum communication cannot directly transmit information, so what is its use? This may be a misunderstanding of quantum communication itself.
Quantum communication does not directly transmit information through quantum. , but use some basic principles of " quantum state " to do other things
For example, encrypting information cannot be cracked in theory. A very important confidential document requires a password to open, and this password , whether you are making a phone call or sending an email, it may be intercepted midway, and quantum communication is definitely more secure.
For example, pass a large string of "1010011010011" to the other party, and then call them to tell them to pick out the passwords such as , 3, 5, 7, 9, and it doesn't matter even if the phone is bugged, because the phone is bugged. The reader has no way of knowing what , 3, 5, 7, 9 corresponds to, and it doesn’t matter even if the photon originally intended to be sent to the other side is intercepted midway, it means that the other side did not receive this string of characters. There will be no subsequent phone calls to tell you the password.
Unless the interceptor sent some "fake photons" to the other side, this side did send it and the other side did receive it, but it doesn't matter. If it is true, it should be entangled with this side. If it is false, It's just that we are entangled with others. We first randomly select some and verify them using Bell's inequality to know whether they are true or false.
➡️Can quantum communication be cracked?
Quantum communication cannot be eavesdropped and is very safe, so just find a way to crack it. For example, During World War II , Germany designed the Enigma machine. I originally thought that this kind of code was unbreakable, but it was cracked by Turing . This It even directly affected the outcome of the war.
or the RSA encryption system, which is relatively safe now. The online transactions we use basically use this encryption method, but in theory, as long as the computing power of the computer is strong enough, such as quantum computer can also be used Cracked, If you want to ensure that information is sufficiently secure, you may need a completely random one-time password, and this uses quantum communication.
simply means that we each receive a large string of "0" and "1" , and then first verify whether it has been eavesdropped, and then randomly select some of the characters for encryption, and the other party also uses this Method to decrypt, and it will not be used next time and then re-sent and re-verified by random selection, so quantum communication is safe in all aspects, logically and theoretically, it cannot be eavesdropped or cracked.
➡️ The current status of the application of quantum communication
At present, quantum communication is the most direct field that can be directly applied in practice. However, the current quantum key distribution rarely uses real quantum entanglement , but only when Photon laser communication uses the principle of "BB84 protocol " made in 1984. It is achieved by measuring the horizontal, polarized and vertical polarization of photons by changing several different angles.
Our country’s Mozi satellite is mainly used for quantum communication experiments. It is currently at a very advanced level in the world. Although at present, there are few areas where quantum communication can be applied immediately, but who will be there in the future? You know, maybe it will have very broad applications in the future in a field that is completely unexpected now. I believe that our country also has the strength and ability to light up different technology trees and possess some of the world's leading technologies.
