Confocal imaging from biphoton correlations
Confocal microscopy provides optical sectioning for three-dimensional imaging but conventionally relies on point-by-point scanning and physical pinholes, limiting imaging speed. Here, we demonstrate that confocal sectioning can instead arise directly from quantum measurement, using spatial correlations in entangled biphoton states. Spatially resolved coincidence measurements in a widefield imaging system suppress contributions from out-of-focus planes, producing optical sectioning in parallel across the whole field of view without physical pinholes or mechanical scanning. In addition, this quantum approach obtains an axial response that, as a result of position-momentum entanglement, is $\sqrt{2}$-times narrower than that of classical confocal imaging. Our work establishes biphoton correlations as a mechanism for improved confocal imaging and enables parallel, pinhole-free optical sectioning without mechanical scanning.