Fig. 1: Single-photon superabsorption in solid-state emitters as the time reversal of single-photon superradiance.
From: Single-photon superabsorption in CsPbBr3 perovskite quantum dots
a, Light absorption at the bandgap of semiconductor QDs can be likened to the excitation of a two-level system; in a simplified view, one may picture a large QD (middle schematic) as a multiple of a small QD (left schematic); the oscillator strength of a conventional two-level system is size independent, that is, \({f}_{{{\rm{TLS}}},{{\rm{small}}}}^{\;{{\rm{uncorrelated}}}} \approx {f}_{{{\rm{TLS}}},{{\rm{large}}}}^{\;{{\rm{uncorrelated}}}}\); in a superabsorbing two-level system, however, correlations among the individual absorption contributions enable a giant collective dipole (right schematic) with enhanced system oscillator strength \({f}_{{{\rm{TLS}}},{{\rm{large}}}}^{\;{{\rm{correlated}}}}\gg {f}_{{{\rm{TLS}}},{{\rm{large}}}}^{\;{{\rm{uncorrelated}}}}\). b, Single-photon superabsorption may be realized by the time reversal of single-photon superradiance. c, Oscillator strength fTLS of the two-level system is constant for an uncorrelated electron–hole pair (horizontal dashed line) but increases with the system volume for a superabsorbing (highly correlated) electron–hole pair (dotted arrows).
