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arXiv:2508.14845 · Physical Review A

Quantum interference of distinguishable photons based on spatially resolved measurements

Miguel Ángel Gonz’alez Jaimes, Alejandra Alarcón, Andrés Camilo Quintero, Daniel R. Sabogal, Luca Maggio, Vincenzo Tamma, Daniel F. Urrego, Alejandra Valencia

Published Apr 24, 2026• 0 citations
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Abstract

We present experimental results demonstrating the quantum interference of two photons distinguishable in their transverse momenta, each entering the input ports of a balanced beam splitter. This counterintuitive interference effect is made possible through spatially resolved measurements in the near field, i.e., by resolving the conjugate variable in which the photons are distinguishable. Our experimental findings agree with theoretical predictions. We contrast our results with a non-spatially resolved measurement where averaging over the photons' positions washes out the quantum interference observed in spatially resolved measurements.

DOI
10.1103/npy3-mzrl

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We present experimental results demonstrating the quantum interference of two photons distinguishable in their transverse momenta, each entering the input ports of a balanced beam splitter. This counterintuitive interference effect is made possible through spatially resolved measurements in the near field, i.e., by resolving the conjugate variable in which the photons are distinguishable. Our experimental findings agree with theoretical predictions. We contrast our results with a non-spatially resolved measurement where averaging over the photons' positions washes out the quantum interference observed in spatially resolved measurements.
Multi-photon interference is the foundation of many applications regarding quantum technologies. Notably, the interference of multiple photons, registered using resolved measurements, is related to the permanent of a matrix, a problem known to be a #P-hard task. Traditionally, achieving high-visibility interference requires a high degree of indistinguishability between the interfering photons. However, this restriction can be circumvented by observing interference in the conjugate variables. This method has been successfully demonstrated using resolved measurements in the temporal and frequency domain. In this work, we extend these approaches to the spatial degrees of freedom of light. Theoretically, we demonstrate that the joint probability of detecting two photons at different positions in the output ports (3 and 4) of a beam-splitter is indeed determined by the permanent of a matrix related to the unitary transformation described by the interferometer. From an experimental perspective, we present experimental results for spatially-resolved interference in position for photons that are distinguishable in transverse momentum. We employ a setup to perform spatially-resolved measurements on photons with an adjustable distinguishability in both the central transverse momentum variable and the lateral displacement from the optical axis. This setup provides full simultaneous tunability over the distinguishability in the spatial variables. Additionally, by varying the lateral displacement, we observe how distinguishability in the position impacts the interference pattern. Overall, our results align well with the theoretical model, reinforcing the validity of our approach. Thus, this work offers new insights into the available degrees of freedom for studying of multi-photonic interference and its applications.
We report experimental studies of quantum interference of multiphoton states impinging on a two-port balanced beam splitter. When the distinguishability between the two input paths is increased, we observe a reduction followed by a resurgence of the interference visibility in multiphoton coincidence detection. We ascribe this unusual behavior to the competition among contributions from distinct number state components of the interfering fields. Our results suggest that wave-particle duality gives rise to a wide range of largely unexplored phenomena in multiparticle interference.
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Multi-photon interference can be observed using independently generated photons as input. In the most simple case, these photons meet up at a beam splitter, resulting in quantum interference between transmission and reflection of the photons. Here, we show that non-local multi-photon interference can be implemented by using a mode swap operation to generate entanglement between the photons detected in the outputs of two spatially separated interferometers. The spatial separation of the output photons makes this implementation of multi-photon interference particularly suitable for quantum protocols that distribute quantum information to different parties.