Toward reliable quantum devices: Realizing robust strong coupling at room temperature

Cavity quantum electrodynamics (cQED), which focuses on the strong coupling between single quantum emitters and optical cavities, has emerged as a core foundation for developing next-generation quantum photonic devices. However, while conventional dielectric microcavities feature high quality factors, they suffer from excessively large mode volumes, making it difficult to achieve ultra-strong light–matter interactions at room temperature. Plasmonic nanocavities can overcome the optical diffraction limit and tightly confine electromagnetic fields into deep-subwavelength volumes, thus enabling strong coupling even at the single-emitter level. Nonetheless, the highly inhomogeneous near-field distribution in conventional plasmonic nanocavities causes the coupling strength to be extremely sensitive to the spatial position of individual quantum emitters, severely limiting the reproducibility and stability of strongly coupled systems.

In a study published in Fundamental Research, a team of researchers from Peking University, led by Professor Xiulai Xu, proposed a hybrid cavity strategy. It integrates a bowtie-structured plasmonic nanocavity with a one-dimensional photonic crystal (1DPC) substrate.

"This composite structure reshapes the electric field distribution inside the nanogap, simultaneously delivering stronger field intensity and improved spatial uniformity," shares Xu. 

Using single CdSe/ZnS quantum dots as emitters, the researchers experimentally realized robust room-temperature strong coupling with a vacuum Rabi splitting of up to approximately 170 meV.

"The hybrid cavity not only enhances the coupling strength but also significantly reduces its dependence on the quantum dot position, leading to greatly improved device-to-device consistency," adds Xu.

Time-resolved photoluminescence measurements revealed that the emission lifetime of the quantum dot is reduced by about five times, reflecting the enhanced Purcell effect in the tailored local optical environment.

"Our results provide a reliable and scalable route for constructing solid‑state strong‑coupling cQED systems at room temperature," says Xu. "The robust, uniform, and ultra-strong light-matter interaction demonstrated here holds promise for practical applications including room‑temperature single‑photon sources, single‑photon transistors, and integrated quantum photonic chips."

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Contact the author: Xiulai Xu, Peking University, Beijing 100871, China, xlxu@pku.edu.cn

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