Metacavity Quantum Electrodynamics.

Cavity quantum electrodynamics (cQED) harnesses light-matter interactions to produce nonclassical light states. However, a fundamental challenge lies in simultaneously achieving Purcell enhancement and tailored wave front control within a single cavity, due to conflicting resonator requirements. Here, we overcome this limitation by demonstrating triggered single-photon emission with customizable wave fronts from semiconductor quantum dots embedded in geometric-phase metacavities. These monolithic devices-only 200 nm thick-deliver Purcell-enhanced emission alongside spin-momentum-locked radiation, vortex beams, and holographic patterns depending on the design. The meta-atom lattice provides high-Q optical confinement, while spatially modulated orientations of the elliptical holes enable efficient outcoupling of photons with designed states. This Letter establishes a new paradigm for intrinsically multiplexing metasurface-based wave front shaping with cQED, enabling high-performance quantum light sources from subwavelength-scale monolithic platforms.