Siheyuan (traditional courtyard house): Starting with the Korean War, returning home to take charge

"Forty percent?"

He Yuzhu didn't slam his hand on the table. He gently placed the report on it, which only made Huang Shichang more uneasy. The red curve on the paper plummeted from 100% to 60%, like a wound cut off by a knife.

Huang Shichang swallowed hard. "Dean He, we simulated the space environment in a vacuum tank."

"Simulation?" He Yuzhu looked up. "What did you say at the project review meeting last month? 'Miniaturization does not affect performance,' those were your exact words. Page seventeen of the review minutes, do you want me to turn to it for you?"

Behind Huang Shichang, three young researchers lowered their heads even further. Someone stole a glance at He Yuzhu before quickly averting their gaze. Huang Shichang's knuckles were white as he gripped the report. "The temperature rose from minus fifty degrees to eighty degrees Celsius, causing drift in the light source's frequency-locking mechanism. This wasn't covered during the ground test."

"Not covered?" He Yuzhu stood up, the chair leg scraping the ground with a jarring sound. "The Kunlun spacecraft orbits the Earth sixteen times a day, experiencing sunrise and sunset every ninety minutes. The temperature shocks it experiences are twice as severe as your test. And you're telling me it wasn't covered?"

The radiators in the conference room hissed, and the sound from the hot water pipes was like a sigh. Huang Shichang didn't dare to respond. The young researcher behind him, wearing glasses, moved his lips slightly, then closed them again.

He Yuzhu stared at Huang Shichang for three seconds. "A solution."

"Add an automatic frequency locking circuit." Huang Shichang pulled a palm-sized circuit board from his briefcase. His hand trembled slightly, and the edge of the board tapped against the edge of the table with a crisp sound. He pushed the board over. "It monitors the wavelength of the light source in real time and dynamically compensates for it. It can keep the signal attenuation within 15%. But it will increase the weight by eight kilograms and the power consumption by 15 watts."

He Yuzhu picked up the circuit board and examined it from all angles. The board was covered with solder joints, and a few solder beads hadn't been cleaned properly, reflecting light under the fluorescent lamp. He put the board back on the table without saying a word.

Huang Shichang thought he was about to get angry, so he quickly added, "There's also the issue of polarization drift. In long-distance fiber optic transmission, the signal attenuates by 30% every 50 kilometers, requiring repeaters to restore the quantum state."

How big is the repeater?

Huang Shichang took out a silver-white metal box from another bag. It was about the size of a palm and had two fiber optic ports on the side. He placed the box on the table and pushed it over. "About three kilograms. One can be deployed every eighty to one hundred kilometers."

He Yuzhu picked up the metal box and weighed it in his hand. It was heavy, and the aluminum alloy casing felt cold to the touch. "One for every 100 kilometers. Four for 400 kilometers in near-Earth orbit. Three lines: primary, backup, and emergency, with twelve repeaters. Adding the three main units, the total weight exceeds one hundred kilograms."

He gently placed the metal box back on the table. The bottom of the box made a dull thud when it hit the table.

Huang Shichang's face flushed red. He opened his mouth, then closed it again, then opened it again. "Dean He, that's just the physical characteristic of quantum communication. Without a repeater, the signal can't travel more than 100 kilometers. This isn't an engineering problem—"

"I know it's not an engineering problem," He Yuzhu interrupted him. "You need to fix the thermal stability and polarization drift of the main unit first. In three months, I want to see a prototype that can run continuously for 1,000 hours in a space environment."

"A thousand hours?" Huang Shih-chang was stunned. "The Kunlun's maiden flight was only seven days ago—"

"Seven days is your responsibility. A thousand hours is to tell you not to work within seven days, but to leave enough room for flexibility."

Huang Shih-chang took off his glasses and wiped the lenses. His hands were trembling, and the lenses almost fell to the ground. After putting his glasses back on, he took a deep breath. "There's also the detector issue. The dark count of the single-photon detector is too high, especially in high-temperature environments. The dark count rate of the silicon avalanche diode increases fivefold at 80 degrees Celsius, and the bit error rate soars from 1.2% to 6%."

He Yuzhu turned to Qian Zhiyuan, who was leaning against the doorframe. "Director Qian, can carbon nanotubes solve the heat dissipation problem?"

Qian Zhiyuan straightened up and walked over, picked up the detector test report, read two pages, and shook his head. "Cooling down is only a temporary solution. Silicon avalanche diodes are inherently unsuitable for high-temperature environments. Change the material—indium gallium arsenide. It has higher detection efficiency in the near-infrared band than silicon, a dark count that is an order of magnitude lower, and an operating temperature that can reach 120 degrees Celsius."

"Who's doing this?"

Huang Shichang raised his hand. "The Shanghai Institute of Technical Physics, Chinese Academy of Sciences. They made infrared detectors for the Fengyun satellite, using indium gallium arsenide. But they haven't done single-photon detection for imaging."

He Yuzhu wrote down the names of the Shanghai Institute of Technical Physics in his notebook, the pen tip pressing down so hard it dented the paper. "Go find them and upgrade it to the single-photon level. Tell me how much it will cost and how long it will take."

Huang Shichang jotted down some notes in his crumpled notebook, hesitated for a moment, and then spoke. "The detector has been replaced, so we can reduce the number of repeaters we need. But we can't avoid the inherent losses in the fiber optic cable."

He Yuzhu stood up and walked to the window. The snow in the yard was piled up on both sides, and a snowplow had just driven over it, leaving a wet tire track. He stared at the track for a few seconds, then turned away.

"Director Huang, since the Kunlun spacecraft has traveled so far, the relay needs to be deployed to lunar orbit."

The pencil slipped from Huang Shichang's hand, bounced twice on the ground, and rolled to the corner. He didn't pick it up, but looked up at He Yuzhu, his lips moving slightly. "Lunar orbit?"

"Low Earth orbit is just the first step. In the future, we'll go to the moon and Mars." He Yuzhu's voice wasn't loud, but every word was weighty. "Right now, you're making repeaters the size of a lunchbox; in the future, you'll be making them the size of matchboxes, deploying hundreds or thousands of them, laying them all the way from Earth to the moon. Are you going to start now, or wait until later to catch up?"

Huang Shichang bent down to pick up the pencil and gripped it tightly in his hand. His knuckles turned white from the pressure, and the pencil trembled slightly between his fingers. The three researchers behind him exchanged glances, and the young man with glasses opened and closed his mouth.

"Dean He, replace the detector with indium gallium arsenide, extend the single-hop distance to 100 kilometers, and make the repeater the size of a matchbox." Huang Shichang's throat was dry and his voice was hoarse. "Give me two years."

"I'll give you a year and a half. By next June, I want to see the first engineering prototype that can run continuously for two thousand hours in a vacuum."

Huang Shichang took a deep breath and extended his hand. He Yuzhu shook his hand. Huang Shichang's palms were sweaty, but his grip was tight.

"You're forcing me to make history."

"History is often forced into existence." He Yuzhu released his grip, walked back to the table, picked up the test report, and signed the last page. The pen tip pierced the paper, leaving a small black dot in the ink. "Your liaison with the Shanghai Institute of Technical Physics will be handled by Lao Sun. The funding will go through the Chengshan Research Institute's account."