Exploring synchrony and chaos of parahydrogen-pumped two-compartment radio-frequency amplification by stimulated emission of radiation

A nuclear-spin-based RASER (radio-frequency amplification by stimulated emission of radiation) is an ideal experimental system to explore nonlinear interaction phenomena of nuclear spins coupled via virtual photons to a resonator. This is due to the RASER being stable for several hours, allowing for extended observation of these phenomena. Nonlinear phenomena in multimode RASERs range from mode oscillations in synchrony, frequency shifts, frequency combs, period doublings, and even chaos. These phenomena are observed in a parahydrogen-pumped two-compartment proton RASER. In two independently pumped compartments, the separation in frequency space between the two RASER modes is precisely controlled with a magnetic field gradient. By controlling the mode separation, we can select the type of nonlinear phenomena observed. A key finding is that the ranges of mode separation where chaos and synchrony occur are very close together. The experimental results are supported by numerical simulations, based on two-mode RASER equations.