A collaboration between researchers at the Technical University of Munich, Universidad Autónoma de Madrid, and ICMM-CSIC has demonstrated a groundbreaking way to turn a single-photon emitter into a controlled multiphoton source. The work, published in Science Advances (Kim et al., 2025), reveals how subtle control over a quantum emitter’s mean electromagnetic field can unlock new regimes of light emission once thought inaccessible. Traditionally, single-photon sources are engineered to avoid simultaneous emission of multiple photons — a cornerstone for quantum communication and computing. However, the study shows that in coherently driven systems, multiphoton processes are not accidental but intrinsic to the underlying quantum dynamics. By using a finely tuned homodyne setup, the team introduced an external coherent field to interfere with the emitter’s own mean field. This “mean-field engineering” allowed them to switch between single-, two-, and even three-photon emission with remarkable precision. “Our results show that even in the simplest quantum system — a two-level emitter — multiphoton correlations can be revealed and controlled,” explains the leading author Elena del Valle (UAM). “It’s a striking reminder that quantum fluctuations play a key role, even when they seem negligible.” This discovery opens new avenues for photonic quantum technologies, including deterministic generation of multiphoton states, photon sorting, and precision control in quantum networks. [Full Article]
