New entangled quantum light: photonic dimer laser*

Laser has been widely utilized in various domains, including the excitation of molecules in fluorescence microscopy and the encoding of information in laser communication. Nonetheless, laser light consists of linear superpositions of Fock states of independent photons, which represents only one of the simplest forms of possible quantum photonic states. As many nonlinear optical processes are very inefficient, if photon-photon correlations could be created, nonlinear process efficiency can be improved by orders of magnitude. I will discuss a new type of coherent quantum light source that, instead of independent photons, outputs a coherent state of the photonic dimers. Photonic dimer is a pair of temporally and spatially entangled photons that exhibit a strong bunching correlation, which has been shown to improve the performance of two-photon excitation microscopy and optical quantum computing. 

We show that a specially designed optical cavity can shape the optical spectrum of the spontaneous parametric down-conversion (SPDC) photon pairs to create coherent states of photonic dimers. We provide a comprehensive discussion of correlation functions. At the weak-pumping limit, our predictions and the experimental results are in excellent agreement. The strong inter-photon correlations also make it possible to transform many nonlinear processes into linear ones, opening up new possibilities in quantum imaging, and advancing our understanding of the collective behaviors of many-photon systems.