Observation of genuine tripartite entanglement and tri-squeezing in the output field of a 3-photon parametric down-conversion process

Nonlinear processes and non-Gaussian states are critical resources for continuous-variable quantum computation, communication, and sensing schemes. In previous work, we demonstrated the generation of single- and multi-mode non-Gaussian states using a nonlinear three-photon down-conversion process in a flux-pumped superconducting parametric cavity [1]. We have now successfully observed key quantum properties, including Wigner negativity and genuine tripartite non-Gaussian entanglement. In particular, we confirm the generation of a Wigner-negative tri-squeezed state for a single-mode down-conversion process. We also confirm the entanglement of the down-converted photons distributed across three modes using an entanglement witness, characterizing the system over a range of drive strengths. These states are observed in the output field of a parametric cavity, i.e., in propagating states of light.

[1] C. W. S. Chang et al., “Observation of three-photon spontaneous parametric down-conversion in a superconducting parametric cavity,” Physical Review X, vol. 10, no. 1, Jan. 2020. doi:10.1103/physrevx.10.011011