Weak-field expansion: A time-closed solution of quantum three-wave mixing
Phys. Rev. A 114, 053705 – Published 5 November, 2026
DOI: https://doi.org/10.1103/wq1z-xymz
Abstract
We present a systematic derivation of the Heisenberg evolution of a trilinear bosonic Hamiltonian system in the presence of a strong drive beyond the standard approximation of a classical, undepleted driving field. We employ a perturbative expansion of the Hamiltonian propagator in orders of the input field amplitudes, as opposed to the standard Baker-Campbell-Hausdorff (BCH) expansion of the propagator in orders of time. Our method automatically provides time-closed expressions and converges considerably faster than BCH expansion, especially in the regime of high parametric gain because the small parameter it uses is natural to the problem. We obtain the well-known quantum solution for optical parametric amplification of down-conversion simply as the first order of the expansion and present the rigorous procedure to derive higher-order corrections one by one. To demonstrate the utility of higher corrections, we discuss the second-order correction to the pump field as an ideal detector of time-energy entanglement in parametric down-conversion. We also use the third-order correction to calculate the limits on the achievable squeezing with parametric amplification and on the fidelity of quantum-state transfer from one optical mode to another with sum (difference) frequency generation, due to the quantum properties of the strong driving field.
