Cesium atoms and quantum dots generate indistinguishable photons for modular quantum networks
Large-scale quantum communication networks require both reliable quantum memories and coherent single-photon sources that can exchange quantum information efficiently. A coherent source of single photons ...
Large-scale quantum communication networks require both reliable quantum memories and coherent single-photon sources that can exchange quantum information efficiently. A coherent source of single photons with narrow linewidth, high brightness, spectral uniformity and compatibility with quantum memories is necessary. While a variety of single-photon sources, such as quantum dots (QDs) and atoms in warm vapor cells, have been developed in recent years, each has inherent limitations, making a scalable and functional quantum network challenging to achieve.
Hybrid quantum architectures that combine different quantum light sources can address these challenges. For example, QDs, which suffer from spectral randomness and are not well suited for photon storage, can be paired with atomic systems that provide reliable frequency standards and quantum memories. In such architectures, QDs can serve as bright, high-rate photon sources, while atomic systems handle photon storage and synchronization.
However, a key challenge in realizing such hybrid quantum architectures is interfacing different quantum light sources. Single photons emitted from different sources exhibit distinct spatial and temporal properties, necessitating modifications and synchronization that introduce losses and increase resource needs.
Indistinguishable photons from unlike sources
In a breakthrough study, a research team led by Professor Han Seb Moon from the Department of Physics at Pusan National University and Professor Je-Hyung Kim from Ulsan National Institute of Science and Technology in the Republic of Korea successfully achieved the generation of indistinguishable photons from two distinct quantum systems. "For the first time, we experimentally demonstrated direct two-photon interference between single photons from two completely independent, physically dissimilar quantum light sources: a warm cesium atomic ensemble and a semiconductor quantum dot (QD)," explains Moon.
Their study was published in the journal Light: Science & Applications on July 15, 2026.
Matching cesium and quantum dots
The researchers used warm cesium vapor cells and self-assembled indium arsenide/gallium arsenide (InAs/GaAs) QDs as independent single-photon sources. Using continuous-wave lasers to excite the cesium atoms, they generated heralded photon pairs consisting of a signal photon at a well-defined wavelength of 917 nm and an idler photon at 852.35 nm.
To match the atomic photon wavelength, the researchers spectrally tuned the QDs by cooling them to 12.4 K (-437°F), producing single-photon emission at 917.48 nm. This resulted in high spectral overlap of 0.88 between the two sources, enabling high-visibility two-photon interference (TPI).
The team then experimentally demonstrated TPI, specifically the Hong–Ou–Mandel effect, between single photons emitted by the QD and heralded signal photons from the warm cesium ensemble under continuous excitation. Hong–Ou–Mandel TPI occurs when two indistinguishable photons enter a beam splitter through different input ports and are detected together in the same output mode. To quantify the TPI, the researchers measured its visibility, the relative contrast between the TPI of indistinguishable and distinguishable photons.
After correcting for the finite time resolution of the detection system, the researchers achieved a high interference visibility of 0.65 ± 0.14, providing direct evidence of sources of indistinguishable single photons. Notably, this was achieved without any spectral or temporal modifications between the two sources.
A route to modular networks
"Our hybrid quantum network bridges the gap between photon generation and storage and provides a global frequency standard for remote quantum emitters," remarks Moon. "In the future, it can become the foundation for modular quantum networks spanning multiple institutions, paving the way for a working quantum internet. Such quantum communication networks could include distributed networks of atomic quantum sensors for navigation or sensing and practical building blocks for scalable quantum computers."
Overall, this innovative hybrid quantum architecture represents an important step toward future quantum network architectures.
Publication details
Kyu-Young Kim et al, Two-photon interference between independent atomic and quantum dot single-photon sources for hybrid quantum network, Light: Science & Applications (2026). DOI: 10.1038/s41377-026-02399-y
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Citation: Cesium atoms and quantum dots generate indistinguishable photons for modular quantum networks (2026, July 30) retrieved 30 July 2026 from https://phys.org/news/2026-07-cesium-atoms-quantum-dots-generate.html
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