Double-slit interference with entangled photons

A theoretical analysis of a double-slit experiment involving entangled photons is presented. It is demonstrated that, under appropriate conditions, two entangled photons with a wavelength of λ can function as a biphoton with a wavelength of λ/2. More intriguingly, we illustrate that even when the two entangled photons are separated by a polarizing beam splitter, they can still exhibit behavior akin to a biphoton of wavelength λ/2. On the experimental front, we explore two distinct quantum interference phenomena using a double-slit setup: the Hanbury Brown and Twiss (HBT) effect, where the photons traverse different slits, and NOON-state interference, in which both photons pass through the same slit. We methodically differentiate the two photons based on their orthogonal polarizations and show that both interference phenomena persist despite their distinguishability at the detectors. This result goes beyond the conventional understanding of two-photon interference and reveals a new nonlocal HBT effect, where interference occurs even in the absence of spatial overlap, fundamentally tied to the concept of entanglement.