Evolution of locally excited avalanches in semiconductors

We show that semiconductor avalanche photodiodes can exhibit diminutive amplification noise during the early evolution of avalanches. The noise is so low that the number of locally excited charges that seed each avalanche can be resolved. These findings constitute an important first step towards realization of a solid-state noiseless amplifier. Moreover, we believe that the experimental setup used, $\mathit{\text{i.e.}}$, time-resolving locally excited avalanches, will become a useful tool for optimizing the number resolution.