Microwave Ionization of H Atoms: Breakdown of Classical Dynamics for High Frequencies

Abstract

We report the first measurements of microwave excitation and ionization of excited hydrogen atoms for scaled frequencies n$co up to 2.8. Classical 3D calculations which directly model this 36.021-GHz experiment agree quite well for n$o) < 1, agree less well for 1 < n$co< 2, and do not agree for n$co > 2. This supports theoretical predictions that as n$co rises above 1, quantal ionization threshold fields rise above those for the onset of classical chaos; however, the data continue to reveal local stability near certain rational frequency ratios that recalls classical behavior.

Non-dispersive wave packets in periodically driven quantum systems

“…(113), (114), as well as by the numerical integration of the classical equations of motion derived from eq. (137). Using this machinery, we illustrate some of the essential properties of nondispersive wave-packets associated with the principal resonance in this system, whereas we postpone the discussion of other primary resonances to section 5.3.…”

“…Fig. 10 compares the phase space structure of the exact classical dynamics generated by the Hamilton function (137), and the isovalue curves of the pendulum dynamics, eq. (144), for the case n 0 = 60, at scaled field strength F 0 = F n 4 0 = 0.01.…”

“…Hence, state of the art experiments are "blind" for the details of the atomic excitation process on the way to ionization, and therefore not suitable for the unambiguous identification of individual eigenstates of the atom in the field, notably of non-dispersive wave-packets. The case is getting worse with additional complications which are unavoidable in a real experiment, such as the unprecise definition of the initial state the atoms are prepared in [133,137,[209][210][211][212][213][214][215][216], the experimental uncertainty on the envelope of the amplitude of the driving field experienced by the atoms as they enter the interaction region with the microwave (typically a microwave cavity or wave guide) [200,211,217], stray electric fields due to contact potentials in the interaction region, and finally uncontrolled noise sources which may affect the coherence effects involved in the quantum mechanical transport process [218]. On the other hand, independent experiments on the microwave ionization of Rydberg states of atomic hydrogen [132,137], as well as on hydrogenic initial states of lithium [217], did indeed provide hard evidence for the relative stability of the atom against ionization when driven by a resonant field of scaled frequency ω 0 ≃ 1.0.…”

“…They are the subject of this section. In most experiments on microwave driven Rydberg atoms, linearly polarized (LP) microwaves have been used [132,133,[135][136][137]. For circular polarization (CP), first experiments were performed for alkali atoms in the late eighties [138,139], with hydrogen atoms following only recently [134].…”

Dynamical localization in the microwave interaction of Rydberg atoms: The influence of noise

“…While in existing experiments on the microwave ionization of hydrogen Rydberg atoms [19][20][21][22][23] at least one of the three parameters is hard to change (e.g., the interaction time), our experimental setup is "universal" in the sense that all three control parameters can easily be varied. Out of the three parameters, the variable interaction time is of particular interest.…”