High-gain effects in broadband continuous-wave parametric down conversion sources and measurements with undetected photons

TL;DR

This paper theoretically investigates how high-gain effects influence the measurement of visible signal spectra in broadband continuous-wave parametric down conversion sources using undetected photons, considering various interferometric configurations and loss scenarios.

Contribution

It provides a detailed theoretical analysis of high-gain effects on undetected photon measurement schemes across different interferometric setups with loss and dispersion, supported by modeling based on a recent PDC source.

Findings

High-gain effects significantly impact measurement outcomes in these schemes.

Different configurations show varying robustness to loss and dispersion.

The analysis identifies optimal operation points for accurate measurements.

Abstract

We study theoretically how high-gain effects affect the measurement outcome of visible signal spectra in undetected photon measurement schemes. We consider two interferometric configurations: firstly, the SU(1,1) interferometer where the idler incurs loss and additional dispersion in between two identical, lossless, squeezers; secondly, the induced coherence interferometer where the idler incurs loss and additional dispersion in between two identical, lossless, squeezers and where the second squeezer is seeded by the idler and a vacuum ancilla mode. Furthermore, we consider a distributed loss configuration where the idler incurs loss as it propagates in the nonlinear medium. Motivated by experimental evidence and due to the fact that broadband sources are ideal for these measurement schemes, we use the dispersive data of a third-order dispersion engineered integrated waveguide parametric down conversion (PDC) source presented in New Journal of Physics 26, 123025 (2024) to model the PDC spectra in the three configurations. For each configuration we consider the case of idler-only (i) absorption, (ii) additional dispersion, and (iii) the combined effects. We obtain results which outline the strength and weaknesses of the different configurations at different operation points.