Many-body theory of quasiparticles in strong laser fields

Few cycle, extreme nonlinear excitations of semiconductors can change electron energy by more than 1eV within a unit cell – without damaging the sample. They can excite and move electronic coherences and quasiparticles between conduction and valence bands much faster than relevant scattering processes, introducing lightwave electronics as the next step for quantum technology. This scenario is highly nonperturbative, and the related optical, quantum-optical, and many-body effects can be systematically described with a first-principles cluster-expansion approach [Semiconductor Quantum Optics, (Cambridge University Press, 2012)]. I will present how this theory quantitatively explains measured high-harmonic (HH) emission [Nat. Photon. 8, 119 (2014)] as well as harmonic sideband (HSB) generation [Nature 533, 225 (2016)] around an optical resonance.
I will explain why the HH generation always involves an intricate interplay between polarization and electronic currents, often within multiple bands of semiconductors, and how electrons can produce a strong quantum interference [Nature 523, 572 (2015)] whenever nonperturbative transitions can mutually dipole couple three bands. This quantum effect produces even-ordered HHs as well as synchronizes the temporal HH emission only with either the positive (negative) crests of the driving field. These properties can be utilized to control polarization direction, temporal, and spectral HH combs, making THz crystallography possible [ Nature Phot. 11, 227 (2017)]. I will also show how HSB radiation reveals structural details of the colliding quasiparticles [ Nature 533, 225 (2016)] and characterizes strong Coulombic and valleytronic effects in monolayer transition metal dichalcogenides.