A new atom-by-atom crystal-building method could finally make long-distance quantum communication possible. Credit: Shutterstock
Creating the same crystal through an alternative method could dramatically extend the reach of quantum networks, increasing their range from only a few kilometers to as much as 2,000 km. This advance brings the prospect of a quantum internet significantly closer to reality.
Quantum computers are extremely fast and capable, yet they remain very challenging to link over long distances.
Until recently, the farthest two quantum computers could communicate through a fiber cable was only a few kilometers. In practical terms, even if a fiber line connected them directly, a quantum computer on the University of Chicago’s South Side campus would still be unable to exchange information with one located in the Willis Tower downtown.
New research published November 6, 2025, in Nature Communications by University of Chicago Pritzker School of Molecular Engineering (UChicago PME) Asst. Prof. Tian Zhong shows that this distance could expand dramatically to 2,000 km (1,243 miles).
Using Zhong’s method, the same UChicago quantum computer that once could not reach the Willis Tower could now, in theory, communicate with a quantum computer situated outside Salt Lake City, Utah.
“For the first time, the technology for building a global-scale quantum internet is within reach,” said Zhong, who recently received the prestigious Sturge Prize for this work.
New research from University of Chicago Pritzker School of Molecular Engineering (UChicago PME) Asst. Prof. Tian Zhong could make it possible for quantum computers to connect at distances up to 2,000 kilometers (1,243 miles), shattering previous records and bringing a quantum internet closer than ever. Credit: UChicago Pritzker School of Molecular Engineering / Jason Smith
Extending coherence times to expand communication distance
Building quantum networks requires linking quantum computers by creating entanglement between atoms sent through a fiber cable. The key factor is how long those entangled atoms can hold their quantum coherence, because longer coherence times make it possible for computers to connect over greater distances.
In their new study, Zhong and his team at UChicago PME increased the coherence time of individual erbium atoms from 0.1 milliseconds to more than 10 milliseconds. In one case, they achieved 24 milliseconds, a level that could theoretically support a connection spanning 4,000 km, which is roughly the distance from UChicago PME to Ocaña, Colombia.
By making rare-earth doped crystals using a technique called molecular-beam epitaxy (MBE) rather than the traditional Czochralski method, the UChicago PME team built components atom by atom with remarkably long-lived quantum coherence. Credit: UChicago Pritzker School of Molecular Engineering / Jason Smith
How a new fabrication method changes performance
The innovation was not in using new or different materials, but from building the same materials a different way. They created the rare-earth-doped crystals necessary to create the quantum entanglement using a technique called molecular-beam epitaxy (MBE) rather than the traditional Czochralski method.
“The traditional way of making this material is by essentially a melting pot,” Zhong said of the Czochralski method. “You throw in the right ratio of ingredients and then melt everything. It goes above 2,000 degrees Celsius and is slowly cooled down to form a material crystal.”
To turn the crystal into a computer component, researchers then chemically “carve” it into the needed form. It’s similar to how a sculptor might select a slab of marble and chip away everything that isn’t the statue.
MBE, however, is more akin to 3D printing. It sprays thin layer after thin layer, building the needed crystal into its exact final form.
The next step for Zhong’s team is to test whether the improved quantum coherence time will translate into quantum computers connecting over greater distances. Credit: UChicago Pritzker School of Molecular Engineering / Jason Smith
“We start with nothing and then assemble this device atom by atom,” Zhong said. “The quality or purity of this material is so high that the quantum coherence properties of these atoms become superb.”
While MBE is a known technique, it has never been used to build this form of rare-earth-doped material. Zhong and his team worked with materials synthesis expert UChicago PME Asst. Prof. Shuolong Yang to adapt MBE for this purpose.
“The approach demonstrated in this paper is highly innovative,” said Institute of Photonic Sciences Prof. Dr. Hugues de Riedmatten, a world leader in the field who was not involved in the research. “It shows that a bottom-up, well-controlled nanofabrication approach can lead to the realization of single rare-earth ion qubits with excellent optical and spin coherence properties, leading to a long-lived spin photon interface with emission at telecom wavelength, all in a fiber-compatible device architecture. This is a significant advance that offers an interesting scalable avenue for the production of many networkable qubits in a controlled fashion.”
Testing long-distance quantum links in the lab
Zhong and his team will next test whether the increased coherence time enables quantum computers to connect to each other over long distances.
“Before we actually deploy fiber from, let’s say, Chicago to New York, we’re going to test it just within my lab,” Zhong said.
This involves linking two qubits in separate dilution refrigerators (“fridges”), both in Zhong’s lab at UChicago PME, through 1,000 kilometers of spooled cable. It’s the subsequent step, but far from the final one.
“We’re now building the third fridge in my lab. When it’s all together, that will form a local network, and we will first do experiments locally in my lab to simulate what a future long-distance network will look like,” Zhong said. “This is all part of the grand goal of creating a true quantum internet, and we’re achieving one more milestone towards that.”
Reference: “Dual epitaxial telecom spin-photon interfaces with long-lived coherence” by Shobhit Gupta, Yizhong Huang, Shihan Liu, Yuxiang Pei, Qiang Gao, Shuolong Yang, Natasha Tomm, Richard J. Warburton and Tian Zhong, 6 November 2025, Nature Communications.
DOI: 10.1038/s41467-025-64780-6
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