Conductance fluctuations in microwave-driven Rydberg atoms

– We draw and quantitatively support a parallel between conductance fluctuations in one-dimensional disordered solids and fluctuations of lifetimes of hydrogen atoms in microwave fields. In particular, we numerically analyze the statistics of scaled atomic resonance widths in the localized regime and we find a lognormal distribution, quantitatively consistent with the theory of Anderson localization. Introduction. – The ionization of hydrogen atoms by linearly polarized microwaves has been a subject of intensive studies for a quarter of this century [1]. Classically, ionization occurs due to the chaotic excitation of the electron in sufficiently strong microwave fields (exceeding the “classical chaos border” [2]). When the microwave frequency ω is smaller than the Kepler frequency of the initial electronic motion ωK, classical and quantum ionization thresholds (i.e. microwave field amplitudes allowing for non-negligeable ionization for sufficiently long microwave pulses) agree. When ω0 = ω/ωK > 1, this is no longer true, because quantum thresholds are then significantly higher than the corresponding classical ones. This experimentally observed effect [3] was beforehand predicted by the so-called photonic localization theory [2]. According to this theory, for fields below a “delocalization border”, the atomic population distribution remains exponentially localized over the ladder of quasi-resonant bound states which are connected to the initial state via a chain of one-photon transitions, such that the population of a bound state which is reached from the initial one by absorbing M photons decreases, on the average, proportionally to exp[−2M/L]. A quantitative prediction