Tunneling in double-well potentials within stochastic quantization: Application to ammonia inversion

Stochastic quantization - introduced by Nelson in 1966 - describes quantum behavior as a conservative diffusion process in which a particle undergoes Brownian-like motion with a fluctuation amplitude set by Planck's constant. While it fully reproduces conventional quantum mechanics, this approach provides an alternative framework that enables the study of dynamical quantities not easily defined within the standard formulation. In the present work, stochastic quantization is employed to investigate tunneling-time statistics for bound states in double-well potentials. Using first-passage time theory within the stochastic quantization framework, both the mean tunneling time, barτ, and the full probability distribution, p(τ), are computed, and the theoretical predictions are validated through extensive numerical simulations of stochastic trajectories for the two potentials considered as representative cases. For the square double-well potential, analytical expressions for barτ are derived and show excellent agreement with simulations. In the high-barrier limit, the results reveal a direct relation between the stochastic-mechanical and quantum-mechanical tunneling times, expressed as τ_QM = (π/2)barτ, where τ_QM corresponds to half the oscillation period of the probability of finding the particle in either well. This relation is further confirmed for generic double-well systems through a WKB analysis. As a concrete application, the inversion dynamics of the ammonia molecule is analyzed, yielding an inversion frequency of approximately 24 GHz, in close agreement with experimental observations. These results highlight the potential of stochastic quantization as a powerful and physically insightful framework for analyzing tunneling phenomena in quantum systems.