Quantum fisher information analysis for absorption measurements with undetected photons Houde, Martin Roeder, Franz Silberhorn, Christine Brecht, Benjamin Quesada, Nicolás <jats:title>Abstract</jats:title> <jats:p> We theoretically compare the quantum Fisher information (QFI) for three configurations of absorption spectroscopy with undetected idler photons: an SU(1,1) interferometer with inter-source idler loss, an induced-coherence (IC) setup in which the idler partially seeds a second squeezer together with a vacuum ancilla, and a distributed-loss (DL) scheme with in-medium attenuation. We calculate the QFI as a function of parametric gain for both full and signal-only detection access. For losses below 99% and low to moderate gain, the SU(1,1) configuration provides the largest QFI. At high gain and intermediate loss, the IC scheme performs best, while under extreme attenuation (transmission <jats:inline-formula> <jats:tex-math> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&lt;</mml:mo> </mml:mrow> </mml:math> </jats:inline-formula> 1%) the DL model becomes optimal. These results delineate the measurement regimes in which each architecture is optimal in terms of information theory. </jats:p> IOP Publishing 2026 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_6501 https://ris.uni-paderborn.de/record/66740 Houde M, Roeder F, Silberhorn C, Brecht B, Quesada N. Quantum fisher information analysis for absorption measurements with undetected photons. <i>Journal of Physics: Photonics</i>. 2026;8(3). doi:<a href="https://doi.org/10.1088/2515-7647/ae82a2">10.1088/2515-7647/ae82a2</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1088/2515-7647/ae82a2 info:eu-repo/semantics/altIdentifier/issn/2515-7647 info:eu-repo/semantics/closedAccess