Motion of a wave packet

C. E. Creffield

We study the dynamics of an Airy wave packet moving in a one-dimensional lattice potential. In contrast to the usual case of propagation in a continuum, for which such a wave packet experiences a uniform acceleration, the lattice bounds its velocity, and so the acceleration cannot continue indefinitely. Instead, we show that the wave packet's motion is described by relativistic equations of motion, which surprisingly arise naturally from evolution under the standard nonrelativistic Schr\"odinger equation. The presence of the lattice potential allows the wave packet's motion to be controlled by means of Floquet engineering. In particular, in the deep relativistic limit when the wave packet's motion is photonlike, this form of control allows it to mimic both standard and negative refraction. Airy wave packets held in lattice potentials can thus be used as powerful and flexible simulators of relativistic quantum systems.

Weimin Ye, Jianlong Liu, Yang Gao +1 more

Nonorthogonality of eigenstates is a fundamental characteristic of non-Hermitian systems. It is expected that nonorthogonality-induced effects could be enhanced in the vicinity of the exceptional points (EPs) where the multiple eigenstates coalesce into one. Here, focusing on the wave-packet motions in non-Hermitian systems, we find that a wave packet near the EPs could exhibit new types of Zitterbewegung- (ZB-) like motion arising from the nonorthogonality of eigenstates. The observed ZB-like motion of a wave packet centered around a single eigenstate contradicts the notion that ZB motion only occurs for a wave packet centered around a superposed state. We further show the existence of a ZB-like motion in the form of an interesting helical trajectory of the wave packet on the incident plane, stemming from the imaginary part of group velocities. These exotic ZB-like motions may provide great insight into nonorthogonal eigenstates and complex eigenfrequencies of non-Hermitian systems.

Phil Attard

A.B. Kukanov, N. D. Naumov, T'hai K'uatig

John A. Yeazell, Carlos R. Stroud

Quantum mechanical wave packet states can approach the classical ideal of a spatially localized particle traveling along a well-defined trajectory. These states offer a system in which the classical limit of quantum atomic theory can be studied. In this work, a wave packet that is radially localized and whose radial motion occurs at the classical orbital period is studied. Despite these strong classical features, the long-term evolution displays the quantum nature of the state. As the wave packet evolves, it becomes dispersed, and the radial motion becomes irregular. However, the wave packet does not remain dispersed, and classical motion returns with the return of the spatial localization. Both the collapse and revival of the wave packet occur because of the quantized nature of the atom. In this experiment, the wave packet was excited to the Rydberg slates by a short, ultraviolet pulse from the ground state of potassium. The probe pulse delay was scanned, and the resulting photo-ionization signal displayed the evolution of the wave packet. The collapse and revival of the radial wave packet were observed.1