Who Is Youlin Chen? Chinese-Born US Nuclear Expert Detained In China Over Espionage Case

US President Donald Trump is expected to ask Chinese President Xi Jinping to release Youlin Chen, a Chinese-born American seismologist who has been detained in China since November 2024 and charged with espionage. Chen worked on US-funded research involving the detection of North Korea's underground nuclear tests.

Chen, 54, was arrested by Chinese state security officers at Beijing International Airport on November 5, 2024, as he prepared to return to the US after visiting family and lecturing at two universities. He was charged with espionage on May 1, 2025, and has not gone on trial.

His wife, Yufang Rong, said the White House assured her that Trump would ask Xi to release Chen when the two leaders meet in Washington this week. Trump had already raised Chen's case with Xi during a visit to Beijing in May, but Rong said that discussion did not lead to his release.

Chen is one of two US citizens whom Washington has designated as “wrongfully detained” in China. The other is Min Zin, a US scholar of Myanmar politics who was detained in June. Reuters reported on September 23 that Trump is expected to press Xi to release both men, although it is unclear whether wider human rights issues will receive the same attention during the summit.

The case centres on the nature of Chen's work. His wife says his research was publicly available and never classified. Chinese authorities say he is suspected of activities that endanger China's national security and violate Chinese law.

Who is Youlin Chen?

Chen was born in China and became a US citizen in 2011. He settled in the Boston area and is a seismologist with a US government contractor, according to Reuters.

His work has included studying seismic signals that can help identify underground nuclear explosions. Such explosions produce shockwaves that can be recorded by monitoring stations. Scientists can analyse those signals to distinguish an explosion from an earthquake and assess factors including its location and size.

His research included analysis of the seismic signatures of North Korea's six known nuclear tests.

Reuters reported that Chen's research was funded by the US State Department and the US Air Force Research Laboratory. His work was openly published, used publicly available data and was carried out in collaboration with Chinese scientists.

Chen had not held a US security clearance, Reuters reported. His family disputes the espionage allegations and says he was conducting scientific research using information available to the public.

China has given a different account. Chinese Foreign Ministry spokesperson Guo Jiakun said the “relevant US person” was suspected of engaging in activities that endangered China's national security and violated Chinese law.

“China is a country with rule of law, and there is no such thing as wrongful detention,” Guo said, without providing further details about the allegations against Chen.

Why was Chen detained in China?

Chen was arrested as he was preparing to fly home after visiting family in China. Rong said he had also lectured at two universities during the trip.

Reuters first revealed his detention in July, months after his arrest. His family and US advocates have since sought greater pressure from Washington for his release.

Rong said Chen has been interrogated more than 100 times about his research. She has also described difficult conditions during his detention and raised concerns about his health and treatment.

US embassy officials have visited Chen for about 30 minutes once a month, but Chinese officials have been present during the meetings, Rong said. She said they read letters she had written to Chen and he dictated his replies. His Chinese lawyer was not allowed to meet him until more than 13 months after his detention, Reuters reported.

Those accounts come from Chen's wife and family and have not been independently established in full. Chinese authorities have not publicly disclosed detailed evidence supporting the espionage charge.

What was Chen's North Korea nuclear research?

Chen's research examined the seismic signatures of North Korea's six known nuclear tests. Reuters reported that the work was funded by the US State Department and Air Force Research Laboratory, used publicly available data and was carried out with Chinese scientists.

Rong believes Chinese authorities may have been interested in Chen's expertise because it could help China detect or conceal underground nuclear tests. She has pointed to “decoupling”, in which a nuclear device is detonated inside a large underground chamber to reduce the seismic signal detected outside. The US has accused China of using the technique to conceal a low-yield nuclear test on June 22, 2020, a claim Beijing denies. There is no public evidence linking that alleged test to Chen's detention, and Chinese authorities have not publicly said that his research on North Korean nuclear tests was the reason for his arrest.

Why is Trump raising Chen's case with Xi?

Chen's detention is now part of the agenda surrounding Xi's visit to Washington.

Rong said she was assured during a meeting at the White House with State Department and National Security Council officials that Trump would ask Xi to release Chen. She said officials also told her that Trump would press Xi over the detention of Min Zin.

Reuters reported that Trump had already raised Chen's case during his May meeting with Xi in Beijing. According to Rong, however, Chen remained detained after that intervention.

Min Zin, a US scholar of Myanmar politics affiliated with the University of California, Berkeley and the think tank ISP-Myanmar, travelled to China in June for an academic workshop and was detained by Chinese state security, according to the Associated Press. His wife has also appealed to Trump to raise his case with Xi.

Reuters reported that the White House has not said whether Trump will raise broader human rights concerns, including issues involving Tibet, Uyghurs and Hong Kong, with Xi.

For Chen's family, the immediate concern is narrower: securing his release.

Trump raised Chen's case with Xi in May. Rong said that did not lead to his release. With Trump expected to raise the case again in Washington, Chen's detention is once more being placed directly before China's leader.