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Rabi oscillations in resonantly driven two-level systems produce an Autler-Townes doublet, whose components can be selectively addressed with chirped pulses and probed via photo-electron spectra. We previously showed 1 that the ionization step depends strongly on the chirp direction — unlike rapid adiabatic passage, where near-complete population inversion occurs regardless of chirp sign. This asymmetry enables absolute control over ionization, allowing the chirp alone to switch a Helium gas between zero and full ionization.
This prediction motivated an experiment by Lukas Bruder's group (Albert-Ludwigs-Universität Freiburg) at the FERMI free-electron laser (Trieste), one of the first quantum-control studies using shaped pulses at such a facility. Targeting the 1st excited state of Helium with circularly polarized pulses ensured strong, clean coupling and a tractable theoretical picture. By propagating the TDSE for a single-active-electron model of Helium, we fully reproduced the measured data, con-firming that chirp-based absolute control of ionization works as predicted 2.
We also report on the response to pulses in which an attenuator was used to cut a "notch" into the pulse spectrum right at the Helium resonance.
1 U Saalmann, S K Giri, and J M Rost, Adiabatic passage to the continuum: Controlling ionization with chirped laser pulses. Phys. Rev. Lett. 121, 153203 (2018).
2 F Richter, U Saalmann, E Allaria, M Wollenhaupt, B Ardini, A Brynes, C Callegari, G Cerullo, M Danailov, A Demidovich, K Dulitz, R Feifel, M D Fraia, S D Ganeshamandiram, L Giannessi, N Gölz, S Hartweg, B von Issendorff, T Laarmann, F Landmesser, Y Li, M Manfredda, C Manzoni, M Michelbach, A Morlok, M Mudrich, A Ngai, I Nikolov, N Pal, F Pannek, G Penco, O Plekan, K C Prince, G Sansone, A Simoncig, F Stienkemeier, R J Squibb, P Susnjar, M Trovo, D Uhl, B Wouterlood, M Zangrando, and L Bruder, Strong-field quantum control in the extreme ultraviolet domain using pulse shaping. Nature 636, 337 (2024).
| Scientific Topics | AMO Physics |
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