Quantum estimation in strong fields: <i>in situ</i> ponderomotive sensing

Strong laser fields find use across physics, particularity in attoscience, where they enable the manipulation of electrons on their natural time scale of attoseconds (10^-18 s). Despite this, many strong laser field parameters can not be accurately measured, particularly the laser intensity, where 20% uncertainty is common. There has been no systematic study of the relationship between these uncertainties and the choice of quantum measurements. However, in quantum metrology, there exists the tools to understand and improve on these uncertainties.

We present the first derivation of quantum and classical Fisher information for attoscience to characterize the laser intensity uncertainty for in situ measurements in strong field ionization. We analytically demonstrate a quadratic dependence of the Fisher informations upon the time the photoelectron is subjected to the laser, which we link to a ‘ponderomotive phase’. We demonstrate that interference effects greatly reduce the laser intensity uncertainty and suggest how to minimize uncertainties in a previous experiment.