Theory of Lightwave-Driven Quantum Electronics in Solids

Abstract

Lightwave electronics is based on the idea of using the instantaneous field of strong optical waves to drive and sculpt electronic states on ultrafast time scales. By utilizing the oscillation cycle of light, electronic currents can be switched thousand times faster than traditional electronics to enable petahertz electronics, properties of electronic states in solids become accessible for quantum information applications, and access to correlated many-body states in solids is provided. In this Thesis, I present a comprehensive many-body quantum theory based on the quantum-dynamic cluster expansion approach to quantitatively describe lightwave-driven many-body excitations in quantum materials. The theory is applied to analyze lightwave excitations in quantitative theory-experiment comparisons which led to the development of an ecosystem of new lightwave-based techniques to characterize quantum materials and probe quantum correlations in situ. The theory is also extended to describe spatially inhomogeneous excitations and nanostructures.

First, the theoretical background of the quantum-dynamic cluster expansion is summarized and the theory to describe lightwave excitations in two-dimensional materials derived. I describe how the resulting semiconductor Bloch equations can be combined with ab initio density-functional theory computations and solved numerically on the full two-dimensional Brillouin zone for a predictive description of the excitation dynamics of realistic materials.

By analyzing the emission dynamics of lightwave-driven coherent excitons in quantum materials, we discovered emergent interference patterns in momentum space, crystal-momentum combs, which precisely locate the emission of harmonic sidebands in momentum space and connect their intensities to the electronic band structure. I apply this connection to reconstruct the band structure from harmonic sideband emission, light that is emitted from a semiconductor in a nonlinear process after excitation with two colors, and demonstrate the approach for two-dimensional tungsten diselenide in a comprehensive theory-experiment comparison.

Harmonic sidebands in solids are generated from lightwave-driven electron-hole recollisions and information about the electronic dynamics is encoded in the emitted light. In a quasiparticle-collider approach, we utilize extremely nonperturbative effects to detect millielectronvolt correlations with attosecond precision, beating the Heisenberg uncertainty limit by two orders of magnitude. We find that strong excitonic correlations in monolayers of tungsten diselenide create a distinct delay in the attoclocking setup compared to a bulk sample with weaker correlations. In a detailed theory-experiment analysis, I demonstrate direct clocking of quasiparticle correlations with attosecond precision which I connect to the dynamics of electron-hole pairs in phase-space using a Wigner-function representation.

The valley-degree of freedom, emergent in some two-dimensional quantum materials, can be switched coherently on ultrafast time scales using lightwave excitations with potential applications in solid-state based classical and quantum-information processing. I apply the developed theory to predict conditions for efficient coherent valleytronic switches and propose how sequencing of multiple switches with petahertz clock rates could be realized and detected experimentally.

Finally, I extend the semiconductor Bloch equations to describe spatial semiconductor and nanostructure excitation by using a Wigner-function based formulation of the single and two-particle correlations for an efficient and intuitive representation in phase space. I find that the spatial dynamics of coherent excitations exhibits a quantum character while electrons, holes, and incoherent excitons show a classical behavior in their spatial kinetics. These properties are identified in a careful theoretical analysis and compared to experimental investigations of the coherent and incoherent dynamics of spatially local excitations.