Fig. 1: Active tuning mechanisms and control of ultrafast radiative loss through selective pumping.

a, Illustration of an initial resonant mode before excitation using 1 − t(ω). As indicated, the mode is defined by three parameters: ω₀, γ_int and γ_rad. b–d, Active tuning approaches for ω₀ (b), γ_int (c) and γ_rad (d). The grey curves are the initial resonances, and the blue curves are the tuned resonances. b, Tuning ω₀ results in a shifted resonance profile although the amplitude and spectral width remain unchanged. c, Tuning γ_int quenches the amplitude of the resonance without fully eliminating it. d, Tuning γ_rad allows the mode to be created as γ_rad increases from zero and fully annihilated as γ_rad decreases to zero. e, Illustration of the temporal symmetry-breaking metasurface, selectively pumped with a 200-fs pulse resonant with a Mie mode in only one of two rods per unit cell indicated by the glowing areas. f, The metasurface initially exhibits an RSP-BIC. The dipole moments of both rods, which have refractive indices n_rod1 = n_rod2, are of equal strength, resulting in an almost perfect antisymmetric mode profile with γ_rad approaching zero. g, After resonant absorption of the pump pulse, the refractive index in rod 1 decreases (n_rod1 < n_rod2), resulting in asymmetric dipole moments and the emergence of the quasi-SP-BIC mode (γ_rad ≠ 0).