Bell test of quantum entanglement in attosecond photoionization

Attosecond physics enables the study of ultrafast coherent electron dynamics in matter upon photoexcitation and photoionization, revealing spectacular effects such as hole migration and coherent Auger dynamics in molecules. In the photoionization scenario, there has been a strong focus on probing the physical manifestations of the internal quantum coherence within the individual parent ion and photoelectron systems. However, quantum correlations between these two subsystems emerging from the attosecond photoionization event have thus far remained much more elusive. In this work, we design theoretically and model numerically a direct probe of quantum entanglement in attosecond photoionization in the form of a Bell test. We simulate from first principles a Bell test protocol for the case of noble gas atoms photoionized by ultrashort, circularly polarized infrared laser pulses in the strong-field regime predicting robust violation of the Bell inequality. This theoretical result paves the way to the direct observation of entanglement in the context of ultrafast photoionization of many-electron systems. Our work provides a different perspective on attosecond physics directed towards the detection of quantum correlations between systems born during attosecond photoionization and unravelling the signatures of entanglement in the ultrafast coherent molecular dynamics, including in the chemical decomposition pathways of molecular ions.