Observation of Subnatural-Linewidth Biphotons in a Two-Level Atomic Ensemble
JyunKai Lin1, TzuHsiang Chien1, ChinTe Wu1*, Ravikumar Chinnarasu1, Shengwang Du2,3,4,5, Ite A. Yu1, Chih-Sung Chuu1
1Department of Physics and Center for Quantum Science and Technology, National Tsing Hua University, Hsinchu 30013, Taiwan
2Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
3Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
4Purdue Quantum Science and Engineering Institute, Purdue University, West Lafayette, Indiana 47907, USA
5Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, USA
* Presenter:ChinTe Wu, email:zqes5207@gmail.com
The generation of narrowband biphotons with subnatural linewidths is essential for realizing efficient light–matter interfaces in quantum networks and quantum memories. In this work, we report the observation of subnatural-linewidth biphotons produced from a simple two-level atomic ensemble driven by a single pump laser. Unlike conventional schemes relying on multi-level configurations or electromagnetically induced transparency (EIT), our approach demonstrates that quantum interference in a minimal two-level system can yield biphotons with an ultranarrow linewidth of 0.36 MHz and high brightness. Moreover, the generated biphotons exhibit a time-symmetric waveform and strong quantum correlations, allowing for heralded single photons with long coherence. This work not only simplifies the generation of narrowband quantum light sources but also opens a promising path toward miniaturized, chip-integrable biphoton sources for scalable quantum communication and photonic quantum information processing (see Lin et al., 2025).

References:
Observation of subnatural-linewidth biphotons in a two-level atomic ensemble, J.-K. Lin, T.-H. Chien, C.-T. Wu, R. Chinnarasu, S. Du, I. A. Yu, and C.-S. Chuu, Phys. Rev. Lett. 134, 043602 (2025).
https://doi.org/10.1103/PhysRevLett.134.043602


Keywords: Atom-Molecular Optical Physics, Quantum Optics, Nonlinear Optics, Biphoton