After eating and drinking, it was time to do some work.In order to complete the last Control of Earth and Moon mission, he had a dozen hurdles to jump over first.

However, just as he was about to get up from his desk, he heard a knock on his office door.

Lu Zhou remembered the appointment he made on the phone yesterday. He threw away his napkins, put away his food container box, and said, “Come in.”

His office door was opened. Director Li appeared at his door. When Director Li saw a food container lying beside the table, he couldn’t help but look surprised.

“… That’s what you ate for lunch?”

Lu Zhou gave him a strange look.

“Yeah, some meat and vegetables, why?”

“Uh, nothing…”

“Let’s just talk about business then. I’m going back to the research institute for a meeting at 3 pm; it’s about the Lunar Orbit Committee.” Lu Zhou looked at the time on his watch and said, “What exactly did you want to tell me on the phone yesterday?”

Director Li didn’t say anything. He just looked at Wang Peng.

Wang Peng nodded. He picked up the food container bag and left the room.

Only two people were left in the office.

Director Li spoke.

“It’s about the quantum encryption algorithm.”

Lu Zhou was intrigued. He raised his eyebrows and asked, “Is it good?”

“It’s great! It’s amazing.” Director Li clapped and said, “You have no idea! After the deputy director of the Institute of Information Engineering saw the algorithm, his jaw was on the floor…”

For some reason, Lu Zhou had a bad feeling about this.

Every time Director Li was nice to him, the old man either wanted something from him or wanted to introduce him to a girl.

“If it’s so good, why are you here?”

Director Li smiled mischievously.

“A while ago, didn’t you say that after the carbon-based topological quantum processor chip comes out, it won’t be long before we can achieve a 1,000 qubit quantum computer?”

Lu Zhou thought for a second and nodded.

“I think I did say that.”

“That’s why I’m here!” Director Li said, “The state held a meeting a few days ago to discuss this issue, but we really need experts in this area. We couldn’t find a solution after discussing for a long time, so…”

“Pause, you don’t need to explain the reason.” Lu Zhou raised his hand and said with a sigh, “You can just tell me what’s wrong.”

“It’s not a big problem, we mainly just want to consult your opinion.” Director Li smiled embarrassedly and asked, “When will a 2,000-qubit computer come out?”

After hearing Director Li’s words, Lu Zhou immediately understood what he was thinking. Director Li was worried about how long the algorithm would stay secure.

After all, this was an understandable concern.

If it was easy to break the bottleneck from 80 to 500, how difficult could it be to go from 500 to 1,000, then 1,000 to 2,000?

Changing an encryption algorithm wasn’t as easy as changing a password. It required a reform from the entire communication field. The hidden social costs couldn’t be measured with money alone.

The state obviously wanted to change the encryption algorithm as few times as possible.

If they had to update the encryption algorithm every three to five years, it would cause huge trouble to China’s financial industry, communications industry, and Internet industry.

“Your worries are not unreasonable,” Lu Zhou said as he tapped his finger on the table. After thinking for a moment, he said, “But this is really hard to say. I can only tell you that the bottleneck of 1,000 qubits will be broken soon. But 2,000 qubits… I have to wait until we achieve 1,000 qubits before I can give you an accurate estimate.”

Director Li said, “Can’t you make a rough estimate?”

“I can, but it’s meaningless.” Lu Zhou sighed and said, “If you just want to feel less anxious, you might as well ask a fortune teller. Also…”

Lu Zhou paused for a second before he continued, “Quantum encryption algorithms are always just temporary. N qubits correspond to 2 to the power of n states, not just 2 times n. In theory, one day, our encryption method won’t be able to keep up with the speed of our technology development.”

The office went silent.

Director Li pondered for a long time. After a while, he asked in a serious way.

“Then, what do you think we should do?”

“We have to solve this problem fundamentally,” Lu Zhou said after thinking for a while. He said, “Which means we have to find another means of communication?”

“So you’re saying… quantum communication?”

Lu Zhou nodded with approval.

“Correct.”

Director Li spoke solemnly.

“But I heard that quantum communication technology is not simple, right? Our country’s research is relatively advanced in this area, yet there aren’t many results. I can’t see this technology maturing anytime soon.”

“That’s not a problem.” Lu Zhou said, “The breakthroughs in this field are mainly focused on achieving quantum entanglement and enhancing the signal strength. The real key to achieving quantum communication is in quantum repeaters.”

Quantum repeaters can also be subdivided into two problems—the problem of “quantum memory” and the problem of “optimizing the quantum read and write efficiency and storage time”.

These two major technical problems were mentioned in the DLCZ protocol, which used a combination of quantum memory and single-photon channel to suppress attenuation and achieve long-distance quantum communication.

However, due to the little progress in quantum memory, quantum communication could only be achieved within a distance of 100 kilometers. The transmission environment was also extremely harsh. This made it impractical to use; some people even suspected it was impossible to popularize this technology.

“Quantum repeater?”

“Yeah.” Lu Zhou looked at Director Li and nodded. He said, “There hasn’t been any progress at all in this area…”

The reason why quantum communication was confidential was because of the special characteristics of the wave function. Once the photon that transmitted the information was intercepted, any observed behavior would cause the collapse of the entangled state, thus destroying the information.

Simply put, if there were a third party C, standing between a phone call among party A and B, no matter what party C did, whether they were using a wiretap or sticking their ear against the wall, the second party C tried to hear something, the entire communication channel would stop.

Asymmetric encryption algorithms and other encryption algorithms were aimed toward traditional communication methods. When it came to quantum communication, encryption was simply unnecessary.

This was the so-called “unbreakable security”!

Lu Zhou spent five minutes briefly explaining the technical difficulties of quantum communication and its advantages over traditional communication methods to Director Li.

Even though Director Li had heard people talk about this idea before, hearing it personally from Academician Lu was different.

After he heard Lu Zhou’s explanation, he quickly asked, “Is this unbreakable quantum communication difficult?”

Lu Zhou nodded seriously.

“Honestly, it’s not just difficult, it’s extremely difficult!

“You just need to know that this bottleneck is completely stopping the commercialization of quantum communication technology.”

The office went silent again.

This silence lasted quite a long time.

Lu Zhou took a sip of water from the cup on the table. He was about to comfort his old friend and tell him not to worry too much. They could use the new set of encryption algorithms for now, and when a 2,000-qubit computer came out, there might be new progress in the research of quantum repeaters.

Any new technology had to take a long time to develop. Even though the quantum encryption algorithm he developed was not particularly brilliant in his own opinion, it was fine for now.

However, when he was about to speak, Director Li spoke first.

“The… The quantum repeater, can you solve it?”

Lu Zhou: “…”