Laser-driven quantum magnonics and terahertz dynamics of the order parameter in antiferromagnets

Abstract

Ultrashort laser pulses can induce picosecond coherent spin precession, described in terms of classical Landau-Lifshitz equations of motion. In antiferromagnets, the optical generation of pairs of high-energy magnons results in coherent 20-THz longitudinal spin oscillations. In a joint theoretical and experimental effort, the authors analyze here this controversial dynamical regime, investigating the dependence of spin dynamics on several parameters, such as temperature, polarization, and fluence. The derivation of an adequate equation of motion requires a quantum mechanical treatment, which predicts also entanglement between the pairs of photogenerated magnons.