Halide perovskites show great potential for a variety of optoelectronic applications. The presence of robust exciton resonance in these materials makes them promising for use in information photonics. In this paper, we demonstrate the possibility of writing and delayed reading of the optical coherence in halide perovskite by the spontaneous (two-pulse) photon echo in
MAPbI3 (
MA+ =
CH3NH3+) lead-halide perovskite single crystal on picosecond time scales. The spectral and polarimetric measurements of the photon echo signal confirm the free excitonic origin of the excitation under study. Observed relatively long dephasing time, high exciton oscillator strength, and weakly pronounced excitation-induced dephasing make halide perovskites a promising media for applications.
Photon echo (PE) spectroscopy is a powerful technique for probing decoherence mechanisms and charge carrier dynamics in semiconductor systems. Beyond traditional coherence measurements, characterizing the photon statistics of the echo signal is important for assessing its potential in quantum information applications and understanding the underlying quantum mechanical processes. Here, we study the photon statistics of PE signals generated by excitons in ensembles of lead halide perovskite CsPbI
3 nanocrystals at cryogenic temperature of 2 K using continuous-variable quantum state optical tomography based on homodyne detection. Pronounced Rabi oscillations of the PE amplitude allow us to evaluate the statistics for various pulse areas in the excitation sequence. The damping of the oscillations with increasing pulse area is attributed to spatial excitation inhomogeneity and excitation-induced dephasing. Despite the large ensemble of optically addressed excitons, the efficiency of generated PE signals is low which is attributed to the complex energy level structure of excitons and non-radiative recombination channels in CsPbI
3 nanocrystals. We analyze the statistical characteristics of PE via the second-order correlation function
g(2)(0) and the characteristic function for different combinations of the areas of the excitation pulses. Our results show that
g(2)(0)=1, and the characteristic function of the PE signal corresponds to classical behavior. The formation of photon echoes as well as
g(2)(0)=1 at the echo time is reproduced by a quantized free-space multimode model. Despite the relatively low efficiency, the photon echo exhibits a high degree of coherence and minimal classical noise, consistent with Poissonian statistics.
Time-resolved and integrated degenerated four-wave mixing experiments with two-photon excitation at a wavelength of 600–710 nm on a 30–40 μm thick cadmium sulfide crystal are presented for a temperature range from 5 to 300 K. A photon echo is observed showing quantum beats both at positive and negative delay times τ with a period of 0.7–0.8 ps. The signal decays exponentially with time constants of ≈170 fs at τ>0 and half as large at τ<0, independent of temperature. The results are discussed in terms of the decay of a high-density gas of e–h pairs, excitons and excitonic molecules highly out of equilibrium.