Femtosecond and Attosecond Phase-Space Correlations in Few-Particle Photoelectron Pulses

Temporal correlations in pulsed electron beams reflect the microscopic dynamics of emission and interparticle interaction. In femtosecond electron emission from nanoscale field emitters, Coulomb interactions result in structured few-electron states with strong correlations in energy, time, and transverse momentum. Interactions with external fields may be used to both probe and further manipulate these correlated states. Here, we combine femtosecond-gated, event-based detection with inelastic electron-light scattering to directly map the photoelectron phase-space distribution of two-electron states. Our experiments demonstrate a bimodal structure in longitudinal phase space, with distinct contributions from interparticle interaction and dispersion. Moreover, we imprint a global phase modulation onto two-electron states and theoretically show that coherent shaping of few-electron phase-space distributions enables attosecond temporal correlations. This controlled phasing of few-electron states can be harnessed to produce tailored excitations and superradiance via two-electron energy postselection.