Bright Chiral Single-Photon Emission Underpinned by Independent Tailoring of Q and V.

The construction of cavity quantum electrodynamic systems is pivotal for advancing the development of quantum emitters, yet it is fundamentally constrained by the trade-off between a cavity's quality factor (Q) and its mode volume (V) in conventional cavities. This causes a bottleneck for single-photon sources when improving the key performance metrics of brightness, purity, and indistinguishability. Here, we overcome this limitation by invoking nonradiative states in the plasmonic metasurface that decouples Q and V. Quasibound states in the continuum regulate electromagnetic field confinement in time (Q) while anapole states enable strong electromagnetic field confinement in space (V). This independent manipulation over Q and V allows us to separately control Purcell factor and cavity linewidth, leading to concurrent improvements of brightness and indistinguishability. Working at room temperature, single-photon emission from two-dimensional hexagonal boron nitride integrated with the plasmonic metasurface is raised by about 3 orders of magnitude. Furthermore, maximal chiral emission is also demonstrated via coordinated spatiotemporal regulation. Our findings pave the way for practical application of compact quantum emitters, and provide new insights into light-matter interaction.