Non-Gaussian quantum states of a multimode light field

Wigner functions that take negative values are considered to be a crucial resource for achieving a quantum computational advantage with continuous variables. In quantum optics, the subtraction (or addition) of a photon from a squeezed state is a common method to generate such Wigner-negativity [1]. But this process has to be made mode-dependent with a multimode environment to prove useful for quantum information. For instance, it was shown that photon subtraction in one mode induces non-Gaussian properties in the modes that are correlated to it [2].
Here we first study theoretically, what are the conditions under which photon subtraction in one mode create Wigner-negativity in a correlated mode? [3]
Then, we generate a multimode Gaussian states from time/frequency modes of an optical frequency comb. Non-Gaussian quantum states, and Wigner negativity, are demonstrated removing a single photon in a mode-selective manner from the multimode environment [4]. We explore the interplay between non-Gaussianity and quantum entanglement and demonstrate large-scale non-Gaussianity with great flexibility along with an ensured compatibility with quantum information protocols.
[1] J. Wenger, et al. Phys. Rev. Lett. 92, 153601 (2004); V. Parigi, et al. Science 317, 1890 (2007).
[2]M. Walschaers, et al. Phys Rev Lett 121, 220501 (2018).
[3]M. Walschaers, et al., PRX Quantum 1, 020305 (2020).
[4] Y.-S. Ra et al, Nature Physics 11, 1 (2019)