Tailoring indistinguishability of photons using longitudinal spatial coherence

Methods to generate photons with tailored indistinguishability are central to developing photonic quantum technologies and making fundamental tests of quantum physics. This study introduces a novel method for manipulating effective longitudinal spatial coherence (LSC) of biphotons, controlling their indistinguishability in a significant manner. The experimental results show that, instead of tailoring the frequency spectrum of the interfering photons, changing their LSC also leads to controlling the width of Hong-Ou-Mandel dip as validated by the theoretical calculations. This powerful approach not only modifies the conventional wisdom claiming only frequency width responsible for indistinguishability control of photons but also positions the LSC as a promising tool for fine-tuning the longitudinal coherence of photons, thereby expanding their potential use in quantum science and technologies.