Publication date: 22nd July 2026
Polaron formation is one of the central processes by which an electronic excitation becomes dressed by a polarizable lattice. Although polarons are usually treated as quasiparticles with defined energies and couplings, their formation is intrinsically dynamical: the lattice polarization must reorganize in time, creating a new many-body state of the material. In this talk, I will describe how coherent multidimensional spectroscopy can directly resolve this birth process in lead-halide perovskite quantum dots.
Using phase-resolved ultrafast spectroscopy with femtosecond time resolution, we show that the anti-diagonal linewidth and inter-excitonic coupling features provide a direct experimental measure of the evolving polaron order parameter. In contrast to conventional II–VI quantum dots such as CdSe, where exciton–phonon coupling is dominated by underdamped normal modes, perovskite quantum dots exhibit overdamped, liquid-like lattice response. The resulting spectral diffusion and delayed growth of coherent inter-excitonic structure reveal the formation of a Landau polaron on a ~100–200 fs timescale.
I will then discuss the quantum-optical consequences of this dynamically generated quasiparticle state. The same polaronic reorganization that dresses the exciton also reshapes the excitonic Hilbert space, enabling delayed electronic coherence, decoherence-protected subspaces, and cooperative optical responses such as superabsorption and time-reversed superfluorescence at elevated temperatures. These results suggest that lead-halide perovskite quantum dots are not simply colloidal quantum objects with strong exciton–phonon coupling, but quantum materials in which collective lattice polarization generates new optical and many-body functionality in real time.
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