Interference of macroscopic beams on a beam splitter: phase uncertainty converted into photon-number uncertainty

TL;DR

This paper demonstrates how phase uncertainty in squeezed-vacuum twin beams can be converted into photon-number fluctuations at a beam splitter, revealing a characteristic distribution shape and potential for filtering macroscopic superpositions.

Contribution

It provides the first experimental observation of phase-to-photon-number uncertainty conversion in light beams, linking quantum phase uncertainty with measurable photon-number distributions.

Findings

Observed 'U-shape' photon-number distribution at beam splitter output.

Demonstrated conversion of phase fluctuations into photon-number fluctuations.

Showed potential for filtering macroscopic superpositions.

Abstract

Squeezed-vacuum twin beams, commonly generated through parametric down-conversion, are known to have perfect photon-number correlations. According to the Heisenberg principle, this is accompanied by a huge uncertainty in their relative phase. By overlapping bright twin beams on a beam splitter, we convert phase fluctuations into photon-number fluctuations and observe this uncertainty as a typical `U-shape' of the output photon-number distribution. This effect, although reported for atomic ensembles and giving hope for phase super-resolution, has been never observed for light beams. The shape of the normalized photon-number difference distribution is similar to the one that would be observed for high-order Fock states. It can be also mimicked by classical beams with artificially mixed phase, but without any perspective for phase super-resolution. The probability distribution at the beam splitter output can be used for filtering macroscopic superpositions at the input.