Adiabaticity parameters for the categorization of light-matter interaction -- from weak to strong driving

TL;DR

This paper categorizes five distinct excitation regimes in light-matter interactions within a two-level system, linking adiabaticity parameters with physical regimes, and provides analytical insights into photon orders and symmetry breaking effects.

Contribution

It introduces a comprehensive classification of excitation regimes based on adiabaticity parameters, connecting Rabi and Landau-Zener physics, with analytical expressions and implications for various physical systems.

Findings

Identified five excitation regimes with clear adiabaticity parameters.

Derived an analytical expression for photon orders connecting different regimes.

Discovered symmetry breaking in adiabatic-impulsive regime with few-cycle pulses.

Abstract

We investigate theoretically and numerically the light-matter interaction in a two-level system (TLS) as a model system for excitation in a solid-state band structure. We identify five clearly distinct excitation regimes, categorized with well-known adiabaticity parameters: (1) the perturbative multiphoton absorption regime for small driving field strengths, and four light field-driven regimes, where intraband motion connects different TLS: (2) the impulsive Landau-Zener (LZ) regime, (3) the non-impulsive LZ regime, (4) the adiabatic regime and (5) the adiabatic-impulsive regime for large electric field strengths. This categorization is tremendously helpful to understand the highly complex excitation dynamics in any TLS, in particular when the driving field strength varies, and naturally connects Rabi physics with Landau-Zener physics. In addition, we find an insightful analytical expression for the photon orders connecting the perturbative multiphoton regime with the light field-driven regimes. Moreover, in the adiabatic-impulsive regime, adiabatic motion and impulsive LZ transitions are equally important, leading to an inversion symmetry breaking of the TLS when applying few-cycle laser pulses. This categorization allows a deep understanding of driven TLS in a large variety of settings ranging from cold atoms and molecules to solids and qubits, and will help to find optimal driving parameters for a given purpose.