Non-Poissonian Ultrashort Nanoscale Electron Pulses.

The statistical character of electron beams used in current technologies, as described by a stream of particles, is random in nature. Using coincidence measurements of femtosecond pulsed electron pairs, we report the observation of sub-Poissonian electron statistics that are nonrandom due to two-electron Coulomb interactions, and that exhibit an antibunching signal of 1 part in 4. This advancement is a fundamental step toward observing a strongly quantum degenerate electron beam needed for many applications, and in particular electron correlation spectroscopy.

Self-organization of topological defects due to applied constraints.

While topological defects are essential to our understanding of self-organizing periodic systems, little is known about how these systems respond when their defects are subjected to geometrical constraints. In an experiment on spatially modulated thermal convection patterns, we observe that applied geometrical constraints bind topological defects into robust self-localized structures that evolve through aggregation, annihilation, and self-replication. We demonstrate that this unexpected cooperative response to the modulation is a natural consequence of three generic elements: phase locking, symmetry breaking, and spatial resonance. Our work provides new insights into the interplay between order, chaos, and control in self-organizing systems.