Quantum Gouy phase singularities in a propagating biphoton state
- 1Kochi University of Technology
Abstract
Phase singularities are topological defects around which the phase winds by an integer multiple of 2 π . In entangled multiphoton states, they can emerge nonlocally in the joint wavefunction rather than in the field of either subsystem alone. Here we show that the quantum Gouy phase generates nonlocal phase singularities (NPSs) in the two-dimensional longitudinal propagation space of entangled photon pairs. We consider photon pairs produced via spontaneous parametric down-conversion pumped by a Laguerre–Gaussian beam, with the signal and idler photons propagating independently over different longitudinal distances. The accumulated radial-mode-dependent Gouy phases induce destructive interference among biphoton spatial-mode components, producing isolated intensity nulls with quantized phase winding. For a pump with radial mode number p , the NPS topological charges have magnitude p , whereas their propagation positions and charge signs are governed by the Rayleigh ranges of the pump and phase-matching functions. We further identify the radial-mode structure required for their formation, showing that separable biphoton states cannot support isolated longitudinal NPSs. Our results extend nonlocal singular optics from transverse spatial correlations to longitudinal propagation dynamics and establish propagation distance as a coordinate space for topological structures in entangled photon pairs.
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BibTeX
@article{jinushi2026quantum,
title = {{Quantum Gouy phase singularities in a propagating biphoton state}},
author = {Takumi Jinushi and Hirokazu Kobayashi},
journal = {New Journal of Physics},
year = {2026},
month = oct,
doi = {10.1088/1367-2630/aeb71c},
url = {https://iopscience.iop.org/article/10.1088/1367-2630/aeb71c},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Quantum Gouy phase singularities in a propagating biphoton state
AU - Takumi Jinushi
AU - Hirokazu Kobayashi
PY - 2026
DA - 2026/10/30
JO - New Journal of Physics
DO - 10.1088/1367-2630/aeb71c
UR - https://iopscience.iop.org/article/10.1088/1367-2630/aeb71c
AB - Phase singularities are topological defects around which the phase winds by an integer multiple of 2 π . In entangled multiphoton states, they can emerge nonlocally in the joint wavefunction rather than in the field of either subsystem alone. Here we show that the quantum Gouy phase generates nonlocal phase singularities (NPSs) in the two-dimensional longitudinal propagation space of entangled photon pairs. We consider photon pairs produced via spontaneous parametric down-conversion pumped by a Laguerre–Gaussian beam, with the signal and idler photons propagating independently over different longitudinal distances. The accumulated radial-mode-dependent Gouy phases induce destructive interference among biphoton spatial-mode components, producing isolated intensity nulls with quantized phase winding. For a pump with radial mode number p , the NPS topological charges have magnitude p , whereas their propagation positions and charge signs are governed by the Rayleigh ranges of the pump and phase-matching functions. We further identify the radial-mode structure required for their formation, showing that separable biphoton states cannot support isolated longitudinal NPSs. Our results extend nonlocal singular optics from transverse spatial correlations to longitudinal propagation dynamics and establish propagation distance as a coordinate space for topological structures in entangled photon pairs.
SN - 1367-2630
ER -