Chasing the Quantum Satellite
wechat_bg

2017-09-19 10:22:01

XINJIANG, Northwest China — As the sun sets behind the Tianshan Mountains, a researcher pulls a lever attached to the dome above, and the Milky Way unfurls overhead. Peering out in the direction of the North Pole on the observation deck of Nanshan Station, he spots Merak, the lowest star in the Big Dipper, roughly where he expects quantum communications satellite Micius to appear in the night sky.

The world’s first quantum satellite, Micius — named after the ancient Chinese philosopher — was launched from the Jiuquan Satellite Launch Center in northern China’s Inner Mongolia Autonomous Region in August last year. This year, on Micius’ 359th day in orbit, the team behind the groundbreaking experiment announced that the satellite had successfully completed its three major goals: quantum entanglement, quantum key distribution, and quantum teleportation.

From mobile phones, to computers, to bank transactions, communications networks have permeated every aspect of modern life. As the security and privacy of such networks can no longer be guaranteed, scientists are looking to quantum technology for impenetrable communications.

The three experiments conducted by Micius are part of a vital foundation for the future of quantum communications technology, according to Pan Jianwei, one of the physicists who spearheaded the project. Pan hopes that by 2030, China will be able to take the lead in creating a global quantum communications network.

The green trail of the satellite Micius is seen in Urumqi, Xinjiang Uyghur Autonomous Region, 2017. Courtesy of Nanshan Station

The green trail of the satellite Micius is seen in Urumqi, Xinjiang Uyghur Autonomous Region, 2017. Courtesy of Nanshan Station

The night Micius was sent into space, top Chinese scientists involved in the project gazed up at the night sky. They were spread across the country, from the vast expanse of the Gobi Desert where the launch took place, to an observatory in southwestern China’s Tibet Autonomous Region. But no matter where they were, their eyes were chasing after the quantum satellite.

A Cipher From the Stars

At 2:32 a.m. on July 25, 2017, Micius made a scheduled pass over Nanshan Station in northwestern China’s Xinjiang Uyghur Autonomous Region.

The satellite operates by transmitting quantum signals called “keys” from its position in space to stations on Earth. These keys consist of strings of photons — the smallest particles that make up a beam of light — emitted in pairs by a light-altering crystal aboard the satellite. Like snow crystals, the keys created with these photons are unique. And any attempt to monitor quantum communications disturbs the paired photons, signaling the presence of an eavesdropper. This makes quantum keys hack-proof — theoretically, at least.

Like all good science, this theory must be proved in experiments such as the one Li Haibing has been conducting at Nanshan. He works on and off throughout the year, but usually, his day begins at dusk. In the summer, brambles prick at his clothes as he makes his way through waist-high grass to reach the Nanshan ground receiving station. In the winter, he trudges through 20 centimeters of snow.

Li must be at his sharpest late at night: Micius doesn’t cross the skies over Nanshan until 2 or 3 a.m., at which point he can receive quantum signals from the satellite. By the time he finishes collecting and organizing his data, it’s usually past 4 in the morning.

A view of Nanshan Station in Urumqi, Xinjiang Uyghur Autonomous Region, July 20, 2017. Jiang Chenyue/Sixth Tone

A view of Nanshan Station in Urumqi, Xinjiang Uyghur Autonomous Region, July 20, 2017. Jiang Chenyue/Sixth Tone

Nights at the station are so quiet that it’s easy to feel cut off from the wider world. Li can tell you how fast the weeds grow there. He and a dog that barks at the beam of his flashlight are the only ones to ever break the silence.

Among the greatest challenges to realizing quantum satellite-based communications is calibrating the beam of photons so that it remains trained on the ground stations receiving the signals. Micius cuts through space at speeds of about 8 kilometers per second. Establishing a stable link between satellite and station is like trying to drop a spinning coin into a piggy bank from a moving plane 10,000 meters above the ground. Every night, Li’s greatest fear is that he won’t be able to “keep up” with Micius.

Birth of the World’s First Quantum Satellite

In 2003, a plan for quantum satellites began to take shape in physicist Pan’s mind. Before the advent of such technology, researchers used traditional fibers for quantum communications, which degraded the photons and limited the potential distance across which data could be shared. A satellite capable of transmitting signals around the globe through the vacuum-like medium of space promised to resolve the issues of scale and data loss.

To demonstrate the project’s viability, Pan’s team first needed to perform ground-based tests. They pored over maps of China searching for a suitable site, finally settling on a tiny island in the middle of northwestern China’s Qinghai Lake — the country’s largest lake, spanning more than 100 kilometers from its northern to southern shores.

Once you send a satellite packed with precision instruments into space, if something breaks, there’s no one up there to fix it.

From 2010 to 2012, the research team lived and worked on Qinghai Lake. Their makeshift lab, little more than a tent atop a mountain, was the only structure on the island aside from a Buddhist convent. During inclement weather, the researchers would each grab one of the poles supporting the tent and hold it in place until the storm passed. In the winter, to prevent the tent’s roof from caving in under the weight of accumulated snow, someone would be sent at regular intervals to sweep it clean.

Designing a satellite able to withstand the harsh conditions of outer space was “like wrestling with monsters,” said Liao Shengkai, a 34-year-old satellite payload director and designer. “The biggest problem,” he said, “is that once you send a satellite packed with precision instruments into space, if something breaks, there’s no one up there to fix it.”

Satellites must be able to navigate violent collisions and vibrations, as well as endure fluctuating temperatures that can heat components to almost 100 degrees Celsius before plunging below zero. Engineers subjected the satellite to a series of tests simulating these conditions. Whenever their equipment suffered damage, Liao and his team would spend all night troubleshooting the problem. Coworkers seeking out Liao in the early hours of the morning knew they could always find him bent over his work at the testing ground.

It took years to complete Micius. This summer, around the one-year anniversary of its launch, the satellite distributed quantum keys to ground stations more than 1,200 kilometers away, shattering the previous world record for quantum-encoded information transfer.

Spooky Action

The observatory in Tibet’s Ngari Prefecture sits at an altitude of 5,100 meters and exists in perpetual winter. Researcher Ren Jigang, 35, first climbed onto the observation platform in 2013 while searching for potential ground-based stations to receive quantum signals from the satellite. He recalls staring into the starry skies, the landscape “untouched by human civilization.” It was then, he said, that he understood why our ancestors were so struck by the heavens, and why they would devote their whole lives to charting patterns in the sky.

Twenty years ago, Ren came across an essay on quantum computing while leafing through a practice book for the gaokao, China’s college entrance exam — a chance encounter that set the path for his future. He went on to study physics at Beijing’s prestigious Tsinghua University. Eight years later, he joined the Micius team, which was tasked with laying the groundwork for quantum teleportation.

Ren Jigang (second from right) poses for a photo beneath the green trail of the satellite Micius in Ngari Prefecture, Tibet Autonomous Region, Oct. 4, 2014. Courtesy of Ren Jigang

Ren Jigang (second from right) poses for a photo beneath the green trail of the satellite Micius in Ngari Prefecture, Tibet Autonomous Region, Oct. 4, 2014. Courtesy of Ren Jigang

From TV shows like “Star Trek,” most of us are familiar with the concept of teleportation: Take a person, break them down into atoms, send these particles elsewhere in the universe, and reassemble them. Theoretically, teleportation would allow people to traverse galaxies in an instant.

While the reality is far humbler, Ren helped verify a nonetheless remarkable phenomenon known as “entanglement,” in which particles can share certain quantum states and affect one another even when separated by enormous physical distance. Albert Einstein, nonplussed at the idea of entanglement, once referred to it as “spooky action at a distance.” But Ren’s team confirmed that entanglement of photon pairs was possible — even with one on Earth and the other more than a thousand kilometers away in space.

During his research, Ren climbed 800 meters from the small town where he lived up to his lab in Ngari each day. The area suffers from electricity shortages; to make sure their equipment functioned properly, Ren and his coworkers had no choice but to keep the heater in the operations room switched off. When they had to remove their gloves to adjust their equipment, Ren said they felt like their skin might freeze to the metal. For a year, he lived in temperatures 20 or 30 degrees below zero, bundling up in thick padded army jackets and cotton blankets. “As long as it’s survivable,” Ren said, “I can manage.”

A New Era

At the start of the rainy season in June, Ren finished a series of experiments in Ngari and returned to Shanghai. To improve his stamina for future fieldwork, he took up aerobic boxing and kickboxing. He calls himself the “Undisputed Champion of Ngari.” Come September, he will head back to the remote area.

A view of the starry night sky over Nanshan Station in Urumqi, Xinjiang Uyghur Autonomous Region, July 23, 2017. Wang Yingxia/Sixth Tone

A view of the starry night sky over Nanshan Station in Urumqi, Xinjiang Uyghur Autonomous Region, July 23, 2017. Wang Yingxia/Sixth Tone

Shortly after Liao tamed the monster that was Micius, he found himself face to face with his next foe. Micius is, after all, just a research and experimental satellite that can only transmit photons on clear nights. Adapting quantum communications to the daytime — and scaling the massive infrastructure necessary to receive transmissions for commercial use — is a very different beast.

With a year left in the satellite’s projected shelf life, the quantum communications team still has plenty of tests to run. Much like Sputnik heralded the beginning of the space age, Ren hopes the Micius project will be remembered as the dawn of a new era for quantum communications — one that could revolutionize the way we transfer information.

Translator: Kilian O’Donnell; editors: Cai Yiwen, Henry Knight, and Denise Hruby.

(Header image: A view of the astronomical telescope at Nanshan Station in Urumqi, Xinjiang Uyghur Autonomous Region, July 25, 2017. Wang Yingxia/Sixth Tone)