If you are full of food, you should do something.

In order to control the last link of the mission chain, there is still a basket of things waiting for him to complete.

However, just as he was about to get up from his desk, there was a sudden knock on the door outside the office.

Thinking of the appointment on the phone yesterday, Lu Zhou probably guessed who it was, and threw the paper towel into the packing box, and then put the plastic bag tightly on the side, clearing the throat and saying.

"Please come in."

The office door was pushed open, and I saw that the familiar and unsatisfactory face of Director Li appeared at the door. He saw the packing box resting on the table, and he was preparing to smile and say hello. His face could not help but reveal. Surprised expression.

"...you eat this at noon?"

Lu Zhou gave him a strange look.

"Two things, one question, is there a problem?"

"Oh, no..."

"I don't have to say anything right. At three o'clock in the afternoon, I have to go back to the Institute of Higher Education to open a meeting on the work of the Lunar Track Construction Committee." When I looked at the time on the watch, Lu Zhou looked at Director Li. Continue to say, "What exactly did you tell me on the phone yesterday?"

Director Li did not speak and looked at Wang Peng.

Wang Peng nodded and took the box and took it out of the office, and took it to the door.

There are only two people left in the office.

Seeing that there were no other people, Director Li said this.

"It's about the quantum encryption algorithm."

As soon as I heard this, Lu Zhou’s eyebrows suddenly asked with interest.

"is it useful?"

"It's easy to use! It's just too good to use." Director Li shot and said, "Have you don't know. After seeing the deputy director of the Institute of Information Engineering of the Chinese Academy of Sciences, I almost surprised." The chin is lying on the ground..."

Seeing this guy's eyebrows and dancing, Lu Zhou always has a bad feeling.

Every time the old man and his courtesy, he is not going to introduce him to the object, that is, there is something to trouble him.

"... Since it is easy to use, what are you doing for me?"

Director Li said with a smile.

"You didn't say that some time ago, after your carbon-based topological quantum processor chip came out, how long would quantum computers break through 1000 qubits?"

Lu Zhou thought for a while and nodded.

"I really want to say it."

"It’s this thing!" He took a hand, and Director Li continued. "The meeting was held a few days ago and it was devoted to this issue. But we really lack experts in this area. We can’t discuss it for a long time. So why..."

"Stop, don't explain the cause and effect to me," Lu Zhou raised his hand and stopped the words of Director Li. He sighed and said, "...you tell me directly what troubles are good."

"It's not a troublesome thing, mainly because I want to consult your opinion," Director Li smiled embarrassedly and asked, "...when is this 2000-qubit computer, when will it come out?"

Upon hearing the words of Director Li, Lu Zhou immediately understood what he was thinking. He had been worried about the timeliness of technology for a long time.

However, it is inevitable that individuals will generally have this concern.

If the bottleneck from 80 to 500 is so easy to break through, it is hard to say how long the technical barriers from 500 to 1000 and from 1000 to 2000 can last.

The replacement of encryption algorithms is not a trivial matter of changing the penguin password. This involves reforms in the entire communications field. The hidden social costs that need to be paid are difficult to measure by money alone.

If you can, the relevant department naturally wants to replace the encryption algorithm once, which can be managed for a little longer.

Don't update the encryption algorithm in three or five years. Even if the financial industry, the communications industry, and the Internet industry in China are so tenacious, they can't stand so toss...

"Your worry is not without reason," the index finger tapped on the table. After Lu Zhou thought for a moment, he said, "But this is really hard to say. I can only tell you that the 1000 qubit bottleneck is Can break through in a short time, but 2000 qubits... At least I have to wait until the 1000 qubits break through and I can give you an accurate estimate."

Director Li is not saying: "Is it impossible to estimate it?"

"It's not an issue that doesn't work, but it doesn't make sense at all," Lu Zhou sighed. "If you just want to make a psychological comfort, you might as well find a fortune-telling question. From a probabilistic point of view, it is all five or five." ......"

After a pause, Lu Zhou continued.

"The quantum encryption algorithm is always only a moment, n qubits correspond to 2^n states, not 2 times n. In theory, if it is only the difficulty of a linear stacking proposition, one day our encryption means will Can't catch up with the speed of our information technology development."

The office was silent.

Repeatedly chewing on the words of Lu Zhou, Director Li pondered for a long time. After a while, he asked seriously.

"What do you think we should do?"

"Only this problem can be solved fundamentally," Lu Zhou said after thinking for a while, "that is, the possibility of eliminating the leak from the means of communication!"

"What do you mean... quantum communication?"

Lu Zhou applauded and nodded.

"Exactly."

Director Li’s expression was a little dignified.

"...but I heard that quantum communication technology is not simple. Our country is still in front of this one, and there are many achievements, but I have never seen the technology mature."

“It’s normal to not see this phenomenon,” Lu Zhou said. “Because the breakthroughs in this field are mainly focused on achieving photon entanglement and enhancing signal strength, the key to realizing quantum communication lies in quantum repeaters. on."

Further subdividing, the quantum repeater can also be subdivided into two propositions of "quantum memory" and "optimization of efficiency and storage time of quantum state writing and reading".

These two technical difficulties, as mentioned in the dlcz scheme, use quantum memory and single-photon channel combination to suppress attenuation to achieve long-distance quantum communication.

However, due to the fact that quantum memory is basically no significant progress, quantum communication can only be achieved within a distance of 100 kilometers, and the requirements of the transmission environment are extremely demanding. This also loses the value of practicality, and even once it is suspected that it is impossible to achieve.

"Quantum repeater?"

"Well," looked at the thoughtful director Li, Lu Zhou nodded. "This piece is not making little progress, but there is no progress at all. This is the same for the whole world..."

The reason why quantum communication can be kept secret is because of the special characteristics of the wave function. Once the photons that transmit information are intercepted, any observation behavior will lead to the collapse of the entangled state.

To put it plainly, call between a and b, if there is a third party c standing in the middle of eavesdropping. Regardless of the means taken by c, using a bug or sticking your ear to the wall, as long as a word is heard by c, a and b will immediately know that the communication is being eavesdropped, and the entire piece of information will lose its meaning.

Including asymmetric encryption algorithms, all encryption algorithms are aimed at traditional communication methods. In the face of quantum communication technology, encryption is simply superfluous.

This is also called "unconditional security"!

It took about five minutes for Lu Zhou to briefly explain the technical difficulties of quantum communication and its advantages over traditional means of communication.

Although they are all things that are often talked about, Mr. Li has heard many people and he have said similar things before, but this time, after all, it is said from the mouth of the Lu Yuanshi, the instantaneous meaning is different.

After listening to Lu Zhou’s explanation, his heart suddenly burst into flames and quickly asked.

"Is this 'unconditional security' quantum communication very difficult?"

Lu Zhou looked at the position seriously.

"To tell the truth, it's not just hard! It's quite difficult!"

"Aside from what I said you can't understand, you just need to know that this stuff is basically the core bottleneck that limits the commercialization of quantum communication technology."

The office was quiet again.

This quiet time is a bit long.

Lu Zhou took a sip of the cup on the table, moistened the mulberry, prepared to comfort the old friend and told him not to be too anxious. That set of encryption algorithms can be used first, and wait until the 2000 qubit computer comes out. There is no new progress in the research of quantum repeaters.

The birth of any new technology takes time to precipitate. Although the quantum encryption algorithm he developed is not particularly clever in his own opinion, it will be no problem for a while.

However, just as he was about to speak, Director Li was able to take a step forward and asked him with a hurry.

"...that, the quantum repeater, can you fix it?"

Lu Zhou: "....................."