In contrast to conventional dynamic light scattering (DLS) measurement via a single sampling volume (SV) observation over a long time span, we propose a novel technique named "photon ensemble correlation spectroscopy" for ultrafast characterization of diffusive particle dynamics through decorrelation analysis of complex-valued DLS scattering signals from an ensemble of independent SVs. We confirm that the ensemble analysis provides a decorrelation-rate-limited ultrafast measurement and demonstrates the feasibility of imaging spatially resolved particle dynamics. Moreover, the use of complex-valued signals gives additional superiority in terms of reliability.