Seminar: Nicole Yunger Halpern (NIST, QuICS, University of Maryland); Wed 09 February 2022


09 February 2022, 4pm (time TBC)
Location: MS Teams online seminar

Quasiprobability distributions resemble probability distributions but can contain negative and imaginary values. Such distributions represent quantum states as probability distributions over phase space represent states in classical statistical mechanics. Many quasiprobabilities exist, the most famous being the Wigner function. Among the least famous ranks the Kirkwood-Dirac distribution, discovered during the early 1900s and then forgotten. But the Kirkwood-Dirac distribution has been enjoying a renaissance recently: Applications range from quantum chaos to tomography, metrology, foundations, and thermodynamics. I will introduce the Kirkwood-Dirac distribution and illustrate its usefulness in metrology: The quasiprobability can be used to prove that operators’ noncommmutation—a nonclassical phenomenon—underlies a protocol’s effectiveness in phase estimation. I aim to convince you that the Kirkwood- Dirac distribution is the best little quasiprobability you’d never heard of.


References
1) Arvidsson-Shukur, NYH, Lepage, Lasek, Barnes, and Lloyd, Nat. Comms. 11, 3775 (2020).
2) Arvidsson-Shukur, Drori-Chevalier, and NYH, J. Phys. A 54, 284001 (2021).
3) Lupu-Gladstein, Yilmaz, Arvidsson-Shukur, Brodutch, Pang, Steinberg, and NYH, arXiv:2111.01194 (2021).
4) NYH, Swingle, and Dressel, Phys. Rev. A 97, 042105 (2018).

Seminar: Gianluca Stefanucci, University of Rome Tor Vergata, Wed 26 January 2022


Online seminar via MS Teams

Title and abstract TBC

Seminar: Nicholas Chancellor, Durham University, Wed 19 January 2022


Currently planned for an online seminar via MS Teams.
Title and abstract TBC

Seminar: Jakub Benda (Charles University, Prague); Wed 8 December


8 December 2021, 3pm
Location: MS Teams online seminar


Multi-photon ionisation of molecules and RABITT in R-matrix method


Processes involving ionisation of molecules by absorption of multiple photons 
proved very useful for experimental analysis of electronic structure and for 
measurement of intrinsic photoionisation delays. Attosecond streaking as well 
as the RABITT interference experiment now serve as widespread tools for 
inspection of attosecond electron dynamics.

In this seminar I will present our on-going theoretical work on above-
threshold multi-photon ionisation of molecules. I will discuss the extension 
of the flexible and widely used one-photon R-matrix method [1] to absorption 
of arbitrary order [2]. The method allows us to compute time-independent 
ionisation amplitudes for all pathways participating e.g. in the RABITT 
measurements, including its higher-order variants. We can then predict the 
measurable sideband delays without resorting to the frequently used, but 
incomplete, asymptotic approaches [3]. At the same time, the time-independent 
theory is typically computationally more efficient than fully general time-
dependent methods [4].

As illustration of the capabilities of the method I will present and compare 
to experiments averaged laboratory-frame time delays for several diatomic and 
polyatomic molecules. Finally, I will discuss some specific interesting 
aspects revealed by the theory, related to the partial wave interference and 
to the effect the channel coupling has on the photoionisation delays.

[1] Benda et al., Phys. Rev. A 102, 052826 (2020)
[2] Benda & Mašín, Sci. Rep. 11, 11686 (2021)
[3] Baykusheva & Wörner, J. Chem. Phys. 146, 124306 (2017)
[4] Brown et al., Comput. Phys. Commun. 250, 107062 (2020)

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