Network nonlocality with continuous variables: probing nonbilocality through pseudospin measurements

Abstract: Quantum networks offer a compelling platform for probing nonlocal correlations beyond the Bell scenario. While network nonlocality has been well studied in discrete-variable (DV) systems, its exploration in continuous-variable (CV) systems remains limited. In this work, we study the bilocal scenario, the simplest quantum network, in a CV framework using pseudospin measurements. We show that two-mode squeezed vacuum (TMSV) states violate the bilocality inequality for any nonzero squeezing, with the violation increasing monotonically and reaching the maximum in the infinite squeezing limit. The robustness of this violation is explored in the presence of local thermal noise. Next, we demonstrate nonbilocality in two key non-Gaussian states, viz., the entangled coherent state and the CV Werner state. Finally, we investigate the enhancement of nonbilocal correlations through photon subtraction applied to the TMSV state. We show that a coherent superposition of single-photon subtractions across modes enables maximal bilocality violation even at zero squeezing, demonstrating non-Gaussianity as a strong resource in the low-squeezing regime. Our findings underscore the potential of CV systems for realizing network-based quantum correlations.