Spatial coherent control of quantum pathways with counter-propagating femtosecond pulse pairs

Abstract

Quantum pathways 5S1/2−5P1/2−5D and 5S1/2−5P3/2−5D in atomic rubidium upon excitation are hard to identify spectrally due to the ultrafast and broadband nature of femtosecond pulses. By introducing additional spatial dimension, counter-propagating pulse pairs entangles the pathway information and the optical paths, and thus can resolve the two pathways in space. In this paper, the spatial coherent control method is employed to identify and manipulate quantum pathways. Square and linear phase-shaping schemes that combine amplitude shaping are proposed for a three-level model system, and the corresponding parameters are carefully fine-tuned to obtain a clear spatial two-photon transition pattern. Local maximums appear in the two-photon transition spatial profile with the square phase-shaping scheme, and the underlying physics is discussed. As well as themselves, the square and linear phase-shaping strategies can also be combined to give two hybrid schemes to well resolve the two pathways of atomic rubidium, and these four schemes can all be employed to manipulate quantum pathways for seeking redirection of all the dynamics to one specific pathway by additionally blocking the specific spectral bands with amplitude modulation.