Survival of the carrier ladder in the high-gain regime

Determine whether the frequency-multiplexed carrier ladder of the folded nonlinear interferometer survives the additional interference terms that arise when the polarization-resolved undetected-photon interferometer is operated in the high-parametric-gain regime.

Background

The paper develops its single-shot Jones-matrix reconstruction in the low-gain regime of spontaneous parametric down-conversion, where each detected event corresponds to interference between single-pair amplitudes. It notes that high-parametric-gain operation changes the noise model and introduces additional intensity and correlation terms. A prior theoretical extension of a polarization-resolved nonlinear interferometer to high gain contains interference contributions absent from the low-gain treatment. The unresolved issue is whether those extra terms preserve the delay-dependent carrier ladder that separates the Jones-matrix elements in a single spectrometer frame. Resolving this question is necessary to establish whether the paper's single-shot multiplexed tomography architecture can be extended reliably to high-gain sources.

References

A polarization-resolved nonlinear interferometer has already been extended theoretically into the high-gain regime in Ref., where interference of the idler at the wave plate adds terms with no low-gain counterpart; whether the carrier ladder survives them is open.

— Single-shot coherent process tomography and mid-infrared polarimetry with undetected photons  (2609.31043 - Zeja et al., 25 Sep 2026) in Section "Discussion and outlook", paragraph "The moment boundary of this line of work", final sentence before the paragraph "Depth-resolved Jones matrices: PS-OCT with undetected photons"