Maximizing hole coherence in ultrafast photoionization of argon with an optimization by sequential parametrization update.

Abstract

Photoionization with attosecond pulses populates hole states in the photoion. 
Superpositions of hole states represent ideal candidates for time-dependent 
spectroscopy, for example via pump-probe studies. The challenge consists in 
identifying pulses that create coherent superpositions of hole states while satisfying
practical constraints. Here, we employ quantum optimal control to maximize the degree 
of coherence between these hole states. To this end, we introduce a derivative-free 
optimization method with sequential parametrization update (SPA optimization). We 
demonstrate the versatility and computational efficiency of SPA optimization for 
photoionization in argon by maximizing the coherence between the 3s and 3p0 hole states
using shaped attosecond pulses. We show that it is possible to maximize the hole 
coherence while simultaneously prescribing the ratio of the final hole state 
populations.