Scientific cell with clamp forming objective lenses. Credit: Covey Lab.
Quantum networks, that is, systems made up of connected quantum computers, quantum sensors or other quantum devices, have the potential to enable faster and more secure communications. The establishment of these networks relies on a quantum phenomenon called entanglement, which involves a link between particles or systems, the quantum state of one influencing the other even when they are far away.
The atomic qubits used so far to establish quantum networks operate at a visible or ultraviolet wavelength, which is not ideal for transmitting signals over long distances via optical fibers. However, converting these signals to telecommunications band wavelengths can reduce communication efficiency and introduce unwanted signals that can disrupt the connection between qubits.
A research team at the University of Illinois at Urbana-Champaign, led by Professor Jacob P. Covey, recently realized a wavelength quantum network in the telecommunications band using an array of ytterbium-171 atoms. Their article, published in Natural physicsintroduces a promising approach to achieve high-fidelity entanglement between atoms and optical photons generated directly in the telecommunications band.
“Networks of quantum devices with shared entanglement present new opportunities in quantum information science,” Xiye Hu, co-author of the paper, told Phys.org.
“Ytterbium-171, classically used in optical atomic clocks due to its long-lived metastable state, has emerged as an ingenious candidate in the atom lattice community with new applications in quantum computing and metrology.”
Laser preparation table. Credit: Covey Lab.
To achieve their quantum network, Hu and his colleagues exploited the unique properties of 171Arrays of Yb atoms, known to hold promise for long-range communications. Their network marks an important step toward realizing a network of quantum processors that can support distributed computing or a quantum network of atomic clocks for precise timing and sensing applications.
“From the metastable state in 171Yb exists a moderately broad transition at 1,389 nm, which we used to achieve time-encoded entanglement between a single atom and a single photon in the telecommunications band with high fidelity,” Hu explained.
“By imaging our one-dimensional array of atoms on a commercial fiber network, we showed that the collection of single photons and subsequent generation of entanglement can be parallelized across the network.”
Overview of the team platform. a, An imaging system with a high numerical aperture objective maps an array of atoms in an optical tweezer to an array of single-mode optical fibers. The team nominally uses a set of 20 tweezers spaced about 4.7 μm apart, but a set of five tweezers spaced about 20 μm apart is used for an optimal match to the MFD of the fiber array. The inset shows the image of a typical V-groove fiber array with ten aligned fibers. b, Researchers’ vision for parallelized networking with atom array processors using fiber, detector, and BS arrays. c, They use time coding to entangle the metastable nuclear spin of ytterbium-171 atoms (blue pulses) with individual photons with a wavelength of 1,389 nm (red pulses). d, After sending the photons through a 40 m fiber, they use TDI and SNSPD to characterize the atom-photon Bell state. Credit: Covey Lab.
Hu and his colleagues demonstrated the feasibility of their parallelized quantum network approach in a series of tests and found that it produced uniformly high entanglement fidelity and negligible crosstalk at different sites in the network. They then also designed an “intermediate networking protocol,” a tool that helps preserve the consistency of data qubits during networking attempts.
“We have studied in detail the physical and technical factors that limit the fidelity of time-encoded atom-photon entanglement, and provided concrete solutions to improve them,” Hu said.
“We showed that 99% fidelity is easily achievable through technical upgrades. Second, we confirmed that the fiber network does not introduce additional sources of error that could hamper entanglement fidelity.”
A key feature of the 171The network of Yb atoms used by the researchers lies in its geometric resemblance to a network of fibers. Hu and his colleagues believe that their network could thus be useful for tackling generalized parallelization tasks (that is, tasks that can be divided into smaller subtasks and executed simultaneously by different qubits or devices in a network).
The design strategies and intermediate networking protocol developed by these researchers could soon be used by other research teams to achieve parallelized quantum networks. The protocol has shown great promise for scheduling network tasks, while maintaining consistency of computation or storage on a single quantum processor within a larger network.
“One of the most substantial improvements we can make in our future work is to move from using an objective lens to using a cavity for collecting single photons,” Hu said. “Among other things, the cavity significantly improves collection efficiency, which significantly improves the networking rate.”
Covey Lab researchers are currently designing a new second-generation ytterbium experiment aimed at achieving high-speed, long-distance communication within a quantum network. In this experiment, the team plans to place their array of atoms inside a macroscopic confocal cavity covered for the 1,389 nm transition.
“The time-encoded atom-photon entanglement demonstrated in our recent work will also eventually be extended to achieve remote atom-atom entanglement, either between two atoms in a single device or between two atoms in two different devices,” Hu added.
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More information:
Lintao Li et al, Quantum telecommunications network parallelized with a lattice of ytterbium-171 atoms, Natural physics (2025). DOI: 10.1038/s41567-025-03022-4. On arXiv: DOI: 10.48550/arxiv.2502.17406
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