Nondispersing Bohr Wave Packets

Long-lived, nondispersing circular, or Bohr, wave packets are produced starting from Li Rydberg atoms by exposing them first to a linearly polarized microwave field at the orbital frequency, 17.6 GHz at principal quantum number $n=72$, which locks the electron’s motion into an approximately linear orbit in which the electron oscillates in phase with the microwave field. The microwave polarization is changed to circular polarization slowly compared to the orbital frequency, and the electron’s motion follows, resulting in a nondispersing Bohr wave packet.

Figure 1

Schematic diagram of the nondispersing Bohr wave packet showing the low point in the potential which rotates about the ion core.

Figure 2

Schematic diagram of the experiments. (a) The Li atomic beam passes through the center of the Fabry-Pérot MW cavity where it is excited by the dye-laser pulses. The $x$- and $y$-polarized MW fields are injected into the cavity through the mirrors, and a field-ionization pulse applied to the lower mirror ionizes the Rydberg atoms and ejects the resulting electrons for detection. (b) Timing diagram. After the dye-laser excitation a $y$-polarized MW pulse is injected into the cavity (—), then an overlapping 90°-phase shifted $x$-polarized pulse of the equal amplitude (- - -). Finally, a field-ionization pulse is applied to the lower mirror. The time-resolved momentum is sampled at times (1) to (4), when the MW field is zero, $y$-polarized, circularly polarized, and $x$-polarized, respectively. (c) The Rydberg electron orbits at times (1) to (4) showing the evolution from an eigenstate to $y$-polarized linear, then circular, and finally $x$-polarized linear wave packets.

Figure 3

Signals observed when atoms are exposed to $y$- and $x$-polarized HCPs and the fine time delay is scanned at the 4 times at the times of (2), (3), and (4) of Fig. 2b. At time (2), with a $y$-polarized MW field (a) $y$-polarized HCP shows motion in the $y$ direction, but (b) obtained with an $x$-polarized HCP shows no motion. At time (3), with a circular polarization, (c) $y$-polarized HCP and (d) $x$-polarized HCP both show motion, with a phase shift. At time (4), $x$-polarized MW field, (e) $y$-polarized HCP shows no $y$ motion, but (f) the $x$-polarized HCP shows $x$ motion.

Figure 4

Signals observed in right- and left-circularly polarized fields, time (3) of Fig. 2b, when scanning the fine delay of the $x$-polarized HCP. (a) $x$-polarized MW field phase shifted by 90°. (b) $x$-polarized field phase shifted by $-90°$.