Theoretical framework for photon subtraction with non-mode-selective resources

This paper establishes a versatile theoretical framework that explicitly describes single-photon subtractionfrom multimode quantum light in the context of non-Gaussian state generation and manipulation. The treatmentfocuses on easy-to-implement configurations in which no mode-selective operation is available and evaluatesfeatures and advantages of schemes where only simple filtering stages are employed on the experiments. Suchconfiguration, by considerably reducing the experimental overheads, makes experiments involving single-photonsubtraction easier to be implemented. The obtained theoretical framework allows retrieving, given a multimodeinput state, optimal conditions required to herald and then to detect non-Gaussian states, providing a practicaland powerful toolbox for experiments' design. The application of the proposed approach to the case study ofSchrödinger cat state preparation starting from a frequency multimode squeezed state illustrates the impact ofthe derived theoretical tools.