When you're full of food and drink, it's time to do something.

In order for Earth Moon to control the last link of the task chain, there are 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 knock on the door outside the office.

Thinking of the appointment on the phone yesterday, Lu Zhou probably guessed who it was, casually threw the tissue into the packing box, then tied the plastic bag tightly and put it aside, cleared his throat and said.

"Please come in."

The door of the office was pushed open, and Director Li's familiar and unsurprised face appeared at the door, and he couldn't help but show a surprised expression on his face when he saw the packing box resting next to the table, and was about to say hello with a smile.

“…… You eat this at noon? ”

Lu Zhou gave him a strange look.

"Two meat and one vegetarian, is there a problem?"

"Uh, no ......"

"Let's get down to business, I'm going back to the Institute for Advanced Study for a meeting at three o'clock in the afternoon, about the work of the Lunar Orbit Construction Committee," Glancing at the time on his watch, Lu Zhou looked at Director Li and continued, "What exactly did you tell me on the phone yesterday?" ”

Director Li didn't speak, and glanced at Wang Peng.

Wang Peng nodded, picked up the packing box and left the office with understanding, and closed the door with him.

There were only two people left in the office.

Seeing that there was no one else, Director Li spoke.

"It's about that quantum encryption algorithm."

As soon as he heard that it was this, Lu Zhou's eyebrows suddenly raised with interest and asked.

"Is it easy to use?"

"Easy to use! It's just so easy to use. Director Li clapped his hands and said with a smile, "You don't know, the deputy director of our Institute of Information Engineering of the Chinese Academy of Sciences was so surprised that he almost didn't knock his chin on the ground after seeing it......

Seeing this guy's eyebrows fluttering, Lu Zhou always had a bad premonition.

Every time the old man was courteous to him, he either intended to introduce him to someone, or he had something to trouble him.

“…… If it's easy to use, why are you still coming to me? ”

Director Li said with a smile.

"Didn't you say some time ago that after your carbon-based topology quantum processor chip comes out, it won't be long before the quantum computer can break through 1000 qubits?"

Lu Zhou thought for a while and nodded.

"I think I did."

"That's for it!" Patting his palms, Director Li continued, "A few days ago, the ministry held a meeting to discuss this issue, but we really lack experts in this area, and we can't discuss the reason for it for a long time......

"Stop, you don't need to explain the cause and effect to me," Lu Zhou raised his hand, stopped Director Li's words, and said with a sigh, "...... You just tell me what's going on. ”

"It's not a hassle, the main thing is that I want to consult your opinion," Director Li smiled embarrassedly and asked, "...... When will this 2000-qubit computer come out? ”

As soon as he heard Director Li's words, Lu Zhou immediately understood what he was thinking, and he was worried about the timeliness of technology for a long time.

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

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

Changing the encryption algorithm is not a trivial matter such as changing the penguin password, which involves the reform of the entire communication field, and the hidden social costs that need to be paid are difficult to measure purely in money.

If it can, the relevant departments naturally hope to change the encryption algorithm once, so that it can be managed for a little longer.

Don't update the encryption algorithm every three or five years, no matter how tenacious the financial, communications, and Internet industries in China are, they can't withstand such a toss......

"Your worries are not unreasonable," Lu Zhou said after a moment of thought with his index finger on the table, "but this thing is really hard to say." I can only tell you that the bottleneck of 1000 qubits can be broken in a short time, but 2000 qubits ...... At least I'll have to wait until 1000 qubits break through before I can give you an accurate estimate. ”

Director Li was puzzled: "Isn't it okay to estimate it?" ”

"It's not a question of whether it will work or not, but it doesn't make sense at all," Lu Zhou sighed, "If you just want to get psychological comfort, it's better to find a fortune teller to ask, from the perspective of probability, it's all five or five anyway." And ......"

After a pause, Lu Zhou continued.

"Quantum encryption algorithms are always temporary, and n qubits correspond to 2^n states, not 2 times n. Theoretically, if it is only a linear stack of propositions, one day our encryption methods will not be able to catch up with the speed of our information technology development. ”

There was silence in the office.

Chewing on Lu Zhou's words repeatedly, Director Li pondered for a long time, and after a long while, he asked seriously.

"What do you think we should do?"

"We can only solve this problem fundamentally," Lu Zhou said after thinking for a while, "that is to say, the possibility of leaking secrets can be eliminated from the means of communication!" ”

"What do you mean...... Quantum communication? ”

Lu Zhou nodded approvingly.

"Exactly."

Director Li's expression was a little solemn.

“…… But I've heard that quantum communication technology is not simple, right? Our country is still relatively ahead in this area, and there are a lot of achievements, but I have never seen the signs of this technology maturing. ”

"It's normal not to see this sign," Lu Zhou said, "because the breakthroughs in this field are mainly focused on realizing photon entanglement and enhancing signal strength, but if you want to truly realize quantum communication, the key lies in quantum repeaters." ”

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

These two technical difficulties are mentioned in the DLCZ scheme, which uses the combination of quantum memory and single-photon channel to suppress attenuation to achieve long-distance quantum communication.

However, due to the fact that there is basically no major progress in the field of quantum memory, quantum communication can only be realized at a distance of less than 100 kilometers, and the requirements for the transmission environment are extremely demanding. And this has lost the value of practicality, and it was even suspected that it was impossible to achieve it.

"Quantum repeaters?"

"Well," looking at the thoughtful Director Li, Lu Zhou nodded, "It's not that there is no progress in this area, but that there is no progress at all." This is the same all over the world......"

The reason why quantum communication can be absolutely secret is because of the special characteristics of the wave function, once the photon transmitting information is intercepted, any observation behavior will lead to the collapse of the entangled state.

To put it in layman's terms, if there is a third party C standing in the middle of the phone call, C is eavesdropping. Regardless of C's means, whether he uses a bug or sticks his ear to the wall, as soon as C hears a word, A and B will immediately know that the communication has been tapped, and the entire message will be meaningless.

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

This is also known as "unconditional security"!

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

Although they are all clichés, and Director Li has heard many people talk about similar things to him before, but this time after all, it came out of Academician Lu's mouth, and the meaning was different in an instant.

After listening to Lu Zhou's explanation, his heart suddenly became hot, and he hurriedly asked.

"Is this 'unconditionally secure' quantum communication very difficult?"

Lu Zhou nodded seriously.

"Honestly, it's not just hard! It's quite difficult! ”

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

The office was quiet again.

This time the silence lasted a little longer.

Lu Zhou picked up the water cup on the table and took a sip, moistened the mulberry, and prepared to comfort the old friend and tell him not to be too anxious. That encryption algorithm can be used first, and when the 2000-qubit computer comes out, maybe there will be new progress in the research of quantum repeaters.

The birth of any new technology takes time to precipitate, and 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 couldn't help but take the lead, and asked anxiously with a monkey on his face.

“…… So, that quantum repeater, can you handle it? ”

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