The interaction of attosecond light pulses with matter often leads to the emission of electron wavepackets. Using techniques such as attosecond streaking or the reconstruction of attosecond beating by interference of two photon transitions (RABBIT), it is possible to measure the spectral amplitude and phase of the emitted wavepackets and gain access to the photoionization dynamics in resonant and non-resonant conditions. In the case of pure wavepackets, the spectral amplitude and phase are sufficient to fully characterize the emitted wavepackets. However, if the reduced quantum state of the photoelectrons is mixed, a complete characterization of the photoelectrons requires measuring the full density matrix, not only an effective amplitude and phase.
In the first part of this talk, I will show how decoherence can arise in attosecond photoelectron spectroscopy. I will focus in particular on recent results in CH4 and CD4 that illustrate the effect of nuclear dynamics on the photoelectron, effectively introducing a finite coherence time in attosecond photoionization experiments. In the second part of the talk, I will discuss a novel quantum state tomography scheme for photoelectrons that can be used to quantify decoherence and electron-ion entanglement.
Albert-Ludwigs-Universität Freiburg, Germany Department of Physics, Lund University, Sweden