An analytical theory of CEP-dependent coherence driven by few-cycle pulses

TL;DR

This paper develops an analytical theory for understanding how the carrier-envelope phase (CEP) influences quantum coherence in a two-level atom driven by a few-cycle pulse, providing insights into CEP-dependent atomic inversion.

Contribution

It introduces a simple, closed-form analytical solution for a two-level atom interacting with a few-cycle pulse without common approximations, highlighting the role of CEP.

Findings

Derived an arithmetic relation between atomic inversion and CEP.

The relation remains robust across different pulse shapes.

Good agreement with numerical simulations confirms the theory's validity.

Abstract

The interaction between an atomic system and a few-cycle ultrafast pulse carries rich physics and a considerable application prospect in quantum-coherence control. However, theoretical understanding of its general behaviors has been hindered by the lack of an analytical description in this regime, especially with regard to the impact of the carrier-envelope phase (CEP). Here, we present an analytical theory that describes a two-level atom driven by a far-off-resonance, few-cycle square pulse. A simple, closed-form solution of the Schrodinger equation is obtained under the first-order perturbation without invoking the rotating-wave approximation or the slowly varying envelope approximation. Further investigation reveals an arithmetic relation between the final inversion of the atom and the CEP of the pulse. Despite its mathematical simplicity, the relation is able to capture some of the key features of the interaction, which prove to be robust against generalization of pulse shapes and show good agreements with numerical solutions. The theory can potentially offer a general guidance in future studies of CEP-sensitive quantum coherence.