Optimization of two-photon absorption for three-level atom

TL;DR

This paper investigates the optimal two-photon states for exciting a three-level atom, revealing how their spectral-temporal properties depend on atomic lifetimes and entanglement, with implications for experimental state preparation.

Contribution

It characterizes the properties of optimal two-photon states for perfect atomic excitation and compares them with experimentally feasible pulse shapes.

Findings

Optimal two-photon states depend on atomic lifetime ratios.

Two interaction regimes are identified based on entanglement impact.

Comparison shows experimentally-relevant pulses can approximate optimal excitation.

Abstract

This work discusses the problem of optimal excitation of a three-level atom of ladder-configuration by light in the two-photon state and coherent light carrying an average of two photons. The applied atom-light interaction model is based on the Wigner-Weisskopf approximation. We characterize the properties of the optimal two-photon state that excites an atom perfectly, i.e. with probability equal to one: We find that the spectro-temporal shape of the optimal state of light is determined by the lifetimes of the atomic states, with the degree of photonic entanglement in the optimal state depends on the lifetime ratio. In consequence, two distinct interaction regimes can be identified in which the entanglement of the input state of light has qualitatively different impact. As the optimal states may be challenging to prepare in general, we compare the results with those obtained for photon pairs of selected experimentally-relevant pulse shapes. As these shapes are optimized for maximal atomic excitation probability, the results can be interpreted in terms of the overlap between the optimal and investigated pulse shapes.