Population difference dynamics in a two-level system under broadband multiphoton excitation by an external field

Allam Srinivasa Rao

Mihai A. Macovei, Fabian Richter, Adriana Pálffy

The quantum dynamics of an externally driven ensemble of nuclear two-level systems embedded in a leaky broadband cavity is investigated theoretically. In the considered scenario both the nuclear ensemble and the cavity mode are coherently pumped by two externally applied x-ray electromagnetic fields. When the frequencies of the applied coherent fields are identical, cross-correlations among the existing decay channels increase the nuclear excitation probabilities depending on the phase difference of the applied fields. Our results show that the excited state of the nuclear ensemble may exhibit sub- to super-Poissonian nuclear statistics, demonstrating induced correlations during photon absorption or emission processes. The role of cross-correlations for the superradiant decay and the collective Lamb shift of the ensemble is also investigated.

Evgeni V. Il’ichev, Sergey N Shevchenko, S. H. W. van der Ploeg +4 more

We study the multiphoton spectroscopy of artificial solid-state four-level quantum system. This system is formed by two coupled superconducting flux qubits. When multiple driving frequency of the applied microwaves matches the energy difference between any two levels, the transition to the upper level is induced. We demonstrate two types of the multiphoton transitions: direct transitions between two levels and ladder-type transitions via an intermediate level. Our calculations show, that for the latter transitions, in particular, the inverse population of the excited state with respect to the ground one is realized. These processes can be useful for the control of the level population for the multilevel scalable quantum systems.

Nikolay N. Bogolubov, Fam Le Kien, A.S. Shumovsky

N. N. Bogolyubov, Fam Le Kien, A. S. Shumovskiǐ

Nirit Dudovich, Dan Oron, Yaron R. Silberberg

By applying pulse shaping techniques to a broadband 100 fs pulse in resonance with a two-level atomic transition, we are able to enhance the peak transient excited level population relative to that achievable with transform limited pulses. We also demonstrate how the dispersion induced by the absorption line itself leads to similar rapidly oscillating transients in the excited population. These transient population effects are applicable in any multiphoton resonant transition.