Multiphoton Rabi oscillations of correlated electrons in strong-field nonsequential double ionization

With quantum calculations, we have investigated the multiphoton nonsequential double ionization of helium atoms in intense laser fields at ultraviolet wavelengths. Very surprisingly, we found a so-far unobserved doublecircle structure in the correlated electron momentum spectra. The double-circle structure essentially reveals multiphoton Rabi oscillations of two electrons, which are strongly supported by the oscillating population of a certain doubly excited state and by the oscillating double ionization signals. This twoelectron multiphoton Rabi effect provides a profound understanding of electronic correlations and complicated multiphoton phenomena and is expected to be a new tool for broad applications, such as quantum coherent control. Electronic correlations are of fundamental importance for the dynamics of many phenomena such as high-temperature superconductivity in solid state. Nonsequential double ionization (NSDI) of atoms and molecules by short intense laser pulses can provide one of the basic examples for studies of dynamical electron correlations, and thus has been investigated extensively both experimentally [1–5] and theoretically [6–10] in the last few decades. Because they possess rich information, the correlated electron momentum spectra [2–5] have revealed a great many physical pictures of electron–electron correlation in NSDI under the recollision mechanism. These physical pictures are well described by the classical recollision 1 Author to whom any correspondence should be addressed. New Journal of Physics 14 (2012) 013001 1367-2630/12/013001+09$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft