Sub-shot-noise correlation of total photon number using macroscopic twin pulses of light

We have measured whole-pulse photon statistics of macroscopic twin pulses of light generated by coherently seeding a two-mode optical parametric amplifier equally in each mode. We are able to produce 300 ps, near-transform-limited twin pulses ({~}10⁶ photons) with a difference photon number having a variance measured to be 73% below the shot-noise level. We have measured probability distributions of the photoelectron difference number, which are the only photoelectron distributions in the macroscopic regime which cannot be explained using standard semiclassical detection theory.