A multidimensional approach to quantum state tomography of photoelectron wavepackets

TL;DR

This paper introduces a novel, efficient quantum state tomography protocol for photoelectron wavepackets that reconstructs the density matrix in a single scan, enabling high-fidelity analysis of complex quantum states.

Contribution

It presents a new single-scan protocol for reconstructing the continuous variable density matrix of photoelectrons using broadband IR and fixed IR reference measurements.

Findings

Achieves high fidelities in density matrix reconstruction.

Successfully estimates the purity of quantum states.

Demonstrates effectiveness on Fano resonance and spin-orbit split states.

Abstract

There is a growing interest in reconstructing the density matrix of photoelectron wavepackets, in particular in complex systems where decoherence can be introduced either by a partial measurement of the system or through coupling with a stochastic environment. To this end, several methods to reconstruct the density matrix, quantum state tomography protocols, have been developed and tested on photoelectrons ejected from noble gases following absorption of extreme ultraviolet (XUV) photons from attosecond pulses. It remains a challenge to obtain model-free, single scan protocols that can reconstruct the density matrix with high fidelities. Current methods require extensive measurements or involve complex fitting of the signal. Efficient single-scan reconstructions would be of great help to increase the number of systems that can be studied. We propose a new and more efficient protocol that is able to reconstruct the continuous variable density matrix of a photoelectron in a single time delay scan. It is based on measuring the coherences of a photoelectron created by absorption of an XUV pulse using a broadband infrared (IR) probe that is scanned in time and a narrowband IR reference that is temporally fixed to the XUV pulse. We illustrate its performance for a Fano resonance in He as well as mixed states in Ar arising from spin-orbit splitting. We show that the protocol results in excellent fidelities and near-perfect estimation of the purity.