The concept of $2n\mathrm{th}$-order squeezing of a quantum field is introduced as a natural generalization of the usual second-order squeezing. It is shown that the processes of degenerate parametric down conversion, harmonic generation, and resonance fluorescence all exhibit higher-order squeezing.

• Received 9 October 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.323