Probing multimode squeezing with correlation functions

TL;DR

This paper introduces a simple, loss-insensitive method using broadband correlation functions to characterize and benchmark multimode squeezers, facilitating their analysis without complex tomography.

Contribution

It presents a novel approach to determine the number and squeezing strengths of multiple multimode squeezers using correlation measurements, avoiding complex state tomography.

Findings

Method effectively characterizes multimode squeezers

Measurements are robust against losses

Approach is less costly than full state tomography

Abstract

Broadband multimode squeezers constitute a powerful quantum resource with promising potential for different applications in quantum information technologies such as information coding in quantum communication networks or quantum simulations in higher dimensional systems. However, the characterization of a large array of squeezers that coexist in a single spatial mode is challenging. In this paper we address this problem and propose a straightforward method to determine the number of squeezers and their respective squeezing strengths by using broadband multimode correlation function measurements. These measurements employ the large detection windows of state of the art avalanche photodiodes to simultaneously probe the full Hilbert space of the generated state, which enables us to benchmark the squeezed states. Moreover, due to the structure of correlation functions, our measurements are not affected by losses. This is a significant advantage, since detectors with low efficiencies are sufficient. Our approach is less costly than full state tomography methods relying on multimode homodyne detection which build on much more demanding measurement and analysis tools and appear to be impractical for large Hilbert spaces.