Complete view of Stark wave-packet evolution

Abstract

Picosecond laser pulses have been used to produce Rydberg wave packets in calcium atoms in the presence of a strong static electric field. The dynamics of the Stark wave packets have been observed by measuring the momentum-space probability distribution as a function of time. The full precession of the electronic orbital angular momentum, the appearance of a large-amplitude, linear oscillation of the electronic dipole moment, and a pronounced, periodic up-down asymmetry in the momentum distribution are all observed directly.A large amount of theoretical and experimental work on Rydberg electron dynamics in a variety of different circum stances has been performed �1�. However, until very re cently, the lack of good experimental techniques to monitor the full time-dependent probability distribution of wave packets has severely limited the insight gained from experi mental data alone, without the aid of theoretical simulations. Nevertheless, comparisons between the results of experi ments and theory have shown that it is possible to produce well-controlled wave packets under a variety of different conditions �1�, and that with alternative methods it is pos sible to experimentally recover their full time-dependent probability distribution with high fidelity �2-4�. In fact, one can now perform dynamics spectroscopy on uncharacterized wave packets. The full electronic motion as viewed in an experiment can be used to interpret the physics behind the motion directly, without relying on theoretical simulations. The refinement of this approach is a necessary prerequisite to controlling wave-packet motion in complex systems where complete quantum mechanical calculations are not readily available.The results presented in this Rapid Communication pro vide a complete experimental view of the time-dependent dynamics of a Rydberg wave packet in combined Coulomb and uniform static electric fields. Although numerous experi mental studies of Stark wave packets have been performed over the last decade �5-7�, this paper describes experiments where the complicated multidimensional evolution of the wave packet can be seen directly. Specifically, the precession of the electronic orbital angular momentum, strong oscilla tions of the electronic dipole moment along the static field direction, and a periodic asymmetry in the momentum distri bution along the static field axis are all linked in the motion of the wave packet and are clearly identified in the measured probability distributions.In the experiment, ground-state 4s4s 1 S 0 Ca atoms in a thermal beam are promoted to an intermediate 4s4 p 1 P 1 level using a 5-nsec dye laser pulse. A 1.5-psec laser pulse then drives a fraction of the excited-state atoms into a 4snd 1 D 2 , 26�n�30 radial Rydberg wave packet �3�. The wave packet is initially localized near the Ca � ion core but immediately propagates radially outward, reflects from the Coulomb potential, and returns to the ion core after one Ke pler period, � K �2�N 3 �3.0 psec �8�. In the absence of the static field, the wave packet...

Displacing Rydberg Electrons: The Mono-Cycle Nature of Half-Cycle Pulses

“…It has experimentally been demonstrated that an ionization probability of 10% of an ensemble of Rydberg atoms scales as F 10% ‫ق‬ 1 n 2 , while a 50% ionization probability scales as F 50% ‫ق‬ 1 n 3͞2 [1,2]. A HCP also appeared to be a good tool to design and manipulate Rydberg wave packets [3] and give a time dependent view of a wave packet [4]. Also a HCP can be used to study weakly bound Rydberg electrons [5].…”

Probing the evolution of Stark wave packets by a weak half-cycle pulse

“…An HCP acting on an electronic wave packet changes the electron energy depending on its instantaneous linear momentum along the direction of the HCP. This feature has enabled experiments in the past that have used directed HCP's to map the time-resolved momentum distribution of the electron in its orbit [13,14]. When the Stark wave packet evolves to high angular momentum, the corresponding classical orbits of the electron are along the lines of constant longitude on the surface of a sphere where the poles are aligned in the direction of the electric field.…”

“…Several detection methods have been used with varying degrees of success, for example, short pulse pump-probe ionization [9], bound statestate interferometry [10], and time-resolved streak camera detection of ionization [11]. Detection of Stark wave packet dynamics has also been successfully demonstrated using HCP's [12,13,14]. In those previous experiments, the detection relies on the fact that an HCP induces a change of electron's total energy, ∆E = p • Q + Q 2 /2, to ionize the electrons.…”

Improving the state selectivity of field ionization with quantum control

“…The nearly macroscopic size of highly excited Rydberg atoms has inspired a variety of experiments that explore quantum-classical correspondence. These include excitation of wavepackets with varying degrees of localization [1][2][3][4][5][6], creation of a Schrödinger cat-like state [7,8], and studies in combined electric and magnetic fields, where an equivalent classical system would exhibit chaos [9][10][11][12]. The large coupling between neighboring Rydberg states allows pairs of atoms to exchange energy in a dipole-dipole interaction [13].…”