Measuring Geometric Phase based on Indefinite Causal Order in a Sagnac Interferometer
Abstract
Sagnac interferometers are important tools for precision measurements. Cancellation of common-path noise ensures a high degree of stability against external perturbations, while their sensitivity to rotations provides the basis of laser gyroscopes. Here we highlight another, less explored feature of Sagnac interferometers: the fact that optical elements are traversed in reverse order for clockwise and counterclockwise propagating light components. This provides the opportunity to explore a classical realization of indefinite causal order, where the order of events within a sequence is not fixed. We explore this concept to identify the geometric phase associated with two non-commuting polarization operations with a single measurement. This idea may have applications for the rapid determination of polarization manipulations or optical activity within chiral media, but foremost it provides a geometric illustration of indefinite causal order.
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BibTeX
@misc{fagundes2026measuring,
title = {{Measuring Geometric Phase based on Indefinite Causal Order in a Sagnac Interferometer}},
author = {Lucas Marques Fagundes and Finlay Campbell and Richard Aguiar Maduro and Renné Medeiros de Araújo and Stephen M. Barnett and Sarah Croke and Sonja Franke-Arnold},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.01540},
eprint = {2610.01540},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.01540},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - Measuring Geometric Phase based on Indefinite Causal Order in a Sagnac Interferometer
AU - Lucas Marques Fagundes
AU - Finlay Campbell
AU - Richard Aguiar Maduro
AU - Renné Medeiros de Araújo
AU - Stephen M. Barnett
AU - Sarah Croke
AU - Sonja Franke-Arnold
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.01540
UR - https://arxiv.org/abs/2610.01540
AB - Sagnac interferometers are important tools for precision measurements. Cancellation of common-path noise ensures a high degree of stability against external perturbations, while their sensitivity to rotations provides the basis of laser gyroscopes. Here we highlight another, less explored feature of Sagnac interferometers: the fact that optical elements are traversed in reverse order for clockwise and counterclockwise propagating light components. This provides the opportunity to explore a classical realization of indefinite causal order, where the order of events within a sequence is not fixed. We explore this concept to identify the geometric phase associated with two non-commuting polarization operations with a single measurement. This idea may have applications for the rapid determination of polarization manipulations or optical activity within chiral media, but foremost it provides a geometric illustration of indefinite causal order.
ER -