  The novel quantum effects induced by the free-electron-photons interaction
have attracted increasing interest due to their potential applications in
ultrafast quantum information processing. Here, we propose a scheme to generate
optical cat states based on the quantum interference of multi-path
free-electron-photons interactions that take place simultaneously with strong
coupling strength. By performing a projection measurement on the electron, the
state of light changes significantly from a coherent state into a non-Gaussian
state with either Wigner negativity or squeezing property, both possess
metrological power to achieve quantum advantage. More importantly, we show that
the Wigner negativity oscillates with the coupling strength, and the optical
cat states are successfully generated with high fidelity at all the oscillation
peaks. This oscillation reveals the quantum interference effect of the multiple
quantum pathways in the interaction of the electron with photons, by that
various nonclassical states of light are promising to be fast prepared and
manipulated. These findings inspire further exploration of emergent quantum
phenomena and advanced quantum technologies with free electrons.
