Few‐Photon Fluorescence From Ultracold Bosons in an Optical Cavity

ABSTRACT Within a cavity quantum electrodynamics framework, we analyse the fluorescent spectrum of ultracold bosons in resonant and second‐harmonic generation (SHG) regimes. Two settings are considered: (i) (few) bosons in an optical lattice and (ii) a trapped two‐component dilute Bose–Einstein condensate (2BEC) within the Bogoliubov scheme. Atom–photon dynamics are treated exactly via time‐dependent configuration interaction, while cavity leakage is modelled via classical oscillator baths. For optical lattices, bosons in short Bose–Hubbard chains with two levels per site show spectral intensity that increases with atom number at weak interactions but decreases and redshifts at strong interactions once atoms outnumber sites. In the 2BEC case, spectra largely scale with particle number when 2BEC–cavity and inter‐particle couplings are rescaled, while strong correlations induce SHG redshifts. These results reveal some generic features of fluorescence in ultracold bosons in optical cavities, and hint at possible experiments and further theoretical developments.