Dynamics of a single Rydberg shell in time dependent external fields*

Abstract

Probabilities for adiabatic or near-adiabatic state transformation within a highly excited shell of Li(n = 25) were studied experimentally and theoretically for a time dependent electric field, E⃗(t), and a constant magnetic field, B⃗. The fields were sufficiently weak and the time dependence slow enough such that only states belonging to the chosen shell were involved. The studies show that the dynamics are governed by the approximate hydrogenic character of the system in most cases, but for some specific time dependences it is influenced strongly by core interactions as expressed through the quantum defects, δl. The s-state is effectively decoupled from the rest of the n = 25 manifold due to a very large quantum defect. However the quantum defects of the p, d and f states are shown to play a decisive role in the dynamics. The core interactions lead to avoided crossings, non-adiabatic state transformations, and possibly even phase-interference effects. When a resonance condition pertaining to the hydrogenic character of the system is fulfilled, a linear Stark state is transformed completely into a circular Stark state oriented along E⃗f.

Multiphoton intrashell resonances in Rydberg atoms: Bloch-Siegert shifts and widths

“…This description is very attractive due to its simplicity and accuracy. It was used recently in analysis of state control by external fields [28], experimental data on microwave ionization resonances [26], adiabatic or near-adiabatic state transformations [29][30][31][32], and intrashell single-photon resonances for circularly polarized fields [33]. It is used here to derive analytical expressions for positions and widths of intrashell multiphoton resonances.…”

“…[29]. In short, a Stark state of maximum polarization [a parabolic state with quantum numbers ͉n 1 , n 2 , m͖ = ͉24,0,0͖ or a coherent elliptic state (CES) of eccentricity e =1 [32]] was formed by laser excitation in a strong electric field ͑145 V / cm͒, then transformed by the adiabatic crossed-field method (ACFM) into a nearly circular CES ͑e Ӎ 0͒ stabilized by a static field [32], and finally exposed to a homogeneous, rotating electric field of frequency ⍀ and amplitude F ⍀ for a time T. The rotation vector of the field, ⍀ ជ , was perpendicular to the static field which in turn was perpendicular to the orbital plane of the circular state.…”

“…These frequencies are much smaller than the orbital frequency of the n = 25 shell ͑421 GHz͒. The transformation was completed in Ͻ10 s and the exposure to the rotating field lasted for T =2 s with switching times of a few field cycles [29]. A ramped electric field of slew rate 420 ͑V/cm͒ / s triggered about 50 s after laser excitation was used to analyze the final distribution of Rydberg states by selective field ionization (SFI) [22], and to determine the probability that the Rydberg atom remained in the original state, i.e., responded adiabatically to the rotating field.…”

“…1). In another version [29,30] the electric field rotated while it approached a constant final value F ជ f perpendicular to B ជ . This was arranged such that 3nF ជ ͑t͒ӍB ជ at an intermediate time t = t c when sharp avoided crossings of quasienergy curves were encountered and purely diabatic transitions brought the CES into a new type of CES.…”

Unidentified transitions in one-photon intrashell dynamics in Rydberg atoms

“…The formation of CESs in external fields was described in [2,3,8]. Intrashell dynamics of the Stark-Zeeman split n = 25 shell in Li was studied extensively over the last 10 years [9][10][11][12][13][14][15][16][17].…”