Determine the origin of four-wave-mixing branch asymmetry

Determine the origin of the strong asymmetry between the positive- and negative-norm Bogoliubov branches observed in four-wave-mixing measurements of driven-dissipative quantum fluids of light, despite theoretical predictions that both branches should be equally visible.

Background

Pump-and-probe and four-wave-mixing measurements probe the susceptibility of a driven-dissipative photon fluid. The Bogoliubov spectrum contains positive- and negative-norm branches, and theory predicts comparable visibility of both branches in four-wave-mixing experiments. However, measurements reported in the cited work show a pronounced asymmetry between them, and the review identifies its physical origin as unresolved.

References

Even though theory predicts that both branches should be equally visible in a four-wave-mixing experiment, measurements performed in have shown a strong asymmetry, whose origin is still unknown.

— Collective excitations of driven-dissipative quantum fluids of light  (2609.40110 - Bramati et al., 30 Sep 2026) in Appendix, subsection “Linear response measurements”