Perovskites—compounds with the CaTiO₃-type crystal structure—show outstanding performance in photovoltaics and multiparameter optical emitters due to their large oscillator strength, strong solar absorption, and excellent charge-transport properties. However, the ability to realize and control many-body quantum states in perovskites, which would extend their application from classical optoelectronic materials to ultrafast quantum operation, remains an open research topic. Here, we generate a cooperative quantum state of excitons in a quantum dot ensemble based on a lead halide perovskite, and we control the ultrafast radiation of excitonic quantum ensembles by introducing optical microcavites. The stimulated radiation of excitonic quantum ensemble in a superlattice microcavity is demonstrated to not be limited by the classical population-inversion condition, leading to a picosecond radiative duration time to dissipate all of the in-phase dipoles. Such a perovskite-assembly superlattice microcavity with a tunable radiation rate promises potential applications in ultrafast, photoelectric-compatible quantum processors.

Metamaterial absorbers (MMAs) offer a novel and flexible method to realize perfect absorption in specific frequencies, especially in the THz range. Despite the exotic abilities to manipulate light, most previously reported MMAs still suffer from limited bandwidth and tunability. Here we present a thermally switchable terahertz (THz) metasurface that exhibits ultra-broadband absorption and high-transmission characteristics at different ambient temperatures. Our simulations demonstrate that at room temperature the structure is highly transparent. When the ambient temperature reaches 358 K, the proposed design exhibits an ultra-broadband absorption from 0.398 to 1.356 THz with the absorptivity maintaining above 90% and the relative absorption bandwidth reaches up to 109.2%. The structure is demonstrated to be insensitive to the incident angle. Moreover, the bandwidth of such a structure can easily be expanded or reduced by cascading or removing the rings, providing high scalability in practical applications. Such a thermally switchable THz metasurface may have potential applications in various fields, such as optical switching, THz imaging, modulating and filtering.

This work presents the saturable absorption (SA) properties of ${\mathrm{CsPbBr}}_3$ perovskite quantum dots (QDs). The perovskite QDs show excellent SA performance with a nonlinear absorption coefficient of $-35\times {10}^{-2}\mathrm{cm}/\mathrm{GW}$ and a figure of merit of $3.7\times {10}^{-14}\mathrm{esu}\mathrm{cm}$. Further, their use as saturable absorbers in a passively $Q$-switched visible solid-state laser for the generation of soliton pulses is demonstrated. These results demonstrate the potential for the perovskite QDs to act as saturable absorbers.

We present theoretically and demonstrate experimentally a tunable and transparent broadband metamaterial absorber with a water-based substrate, and the absorption properties can be tuned by controlling the thickness of the water substrate.