Impact of Polarization Distinguishability on Coherence in QIUP

Quantum imaging with undetected photons (QIUP) is a promising technique for non-invasive imaging, particularly at wavelengths where detectors are inefficient or unavailable. Recent studies have investigated the role of polarization in QIUP schemes. In this work, we examine whether post-generation optical elements can recover interference when the signal photons are distinguishable in polarization at the source. Specifically, we employ a Mach-Zehnder interferometer after the photon pairs are generated from two nonlinear crystals. Our results indicate that polarization distinguishability at the time of generation leads to a loss of interference that cannot be restored by post-generation optical arrangements. This highlights the fundamental importance of indistinguishability at the source for maintaining coherence in QIUP systems.