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We use a non-equilibrium many-body theory that engages the elements oftransient coherence, correlation, and nonlinearity to describe changes in themagnetic and electronic phases of strongly correlated systems induced byfemtosecond nonlinear photoexcitation. Using a generalized tight--binding meanfield approach based on Hubbard operators and including the coupling of thelaser field, we describe a mechanism for simultaneous insulator--to--metal andanti-- to ferro--magnetic transition to a transient state triggered bynon-thermal ultrafast spin and charge coupled excitations. We demontrate, inparticular, that photoexcitation of composite fermion quasiparticles inducesquasi-instantaneous spin canting that quenches the energy gap of theantiferromagnetic insulator and acts as a nonadiabatic "initial condition" thattriggers non-thermal lattice dynamics leading to an insulator to metal andantiferromagnetic (AFM) to ferromagnetic (FM) transitions. Our theoreticalpredictions are consistent with recent ultrafast pump-probe spectroscopyexperiments that revealed a magnetic phase transition during 100fs laser pulsephotoexcitation of the CE--type AFM insulating phase of colossalmagnetoresistive manganites. In particular, experiment observes two distinctcharge relaxation components, fs and ps, with nonlinear threshold dependence ata pump fluence threshold that coincides with that for femtosecond magnetizationphoto excitation. Our theory attributes the correlation between femtosecondspin and charge nonlinearity leading to transition in the magnetic andelectronic state to spin/charge/lattice coupling and laser-induced quantum spincanting that accompanies the driven population inversion between twoquasi--particle bands with different properties: a mostly occupied polaronicband and a mostly empty metallic band, whose dispersion is determined byquantum spin canting.

Theory of Ultrafast Spin--Charge Quantum Dynamics in Strongly Correlated  Systems Controlled by Femtosecond Photoexcitation: an Application to  Insulating Antiferromagnetic Manganites