Mapping atomic trapping in an optical superlattice onto the libration of a planar rotor in electric fields

TL;DR

This paper establishes a mathematical correspondence between atomic trapping in optical superlattices and the libration of planar rotors in electric fields, leveraging quasi-exact solvability to analyze atomic dynamics.

Contribution

It introduces a novel mapping between optical lattice trapping and planar rotor libration, enabling analytic solutions for atomic band structures and dynamics.

Findings

Mapped atomic trapping to a generalized planar pendulum problem

Derived analytic solutions for the band structure of ultracold atoms in superlattices

Characterized atomic squeezing and tunneling through eigenenergy analysis

Abstract

We show that two seemingly unrelated problems - the trapping of an atom in an optical superlattice (OSL) and the libration of a planar rigid rotor in combined electric and optical fields - have isomorphic Hamiltonians. Formed by the interference of optical lattices whose spatial periods differ by a factor of two, OSL gives rise to a periodic potential that acts on atomic translation via the AC Stark effect. The latter system, also known as the generalized planar pendulum (GPP), is realized by subjecting a planar rigid rotor to combined orienting and aligning interactions due to the coupling of the rotor's permanent and induced electric dipole moments with the combined fields. The mapping makes it possible to establish correspondence between concepts developed for the two eigenproblems individually, such as localization on the one hand and orientation/alignment on the other. Moreover, since the GPP problem is conditionally quasi-exactly solvable (C-QES), so is atomic trapping in an OSL. We make use of both the correspondence and the quasi-exact solvability to treat ultracold atoms in an optical superlattice as a semifinite-gap system. The band structure of this system follows from the eigenenergies and their genuine and avoided crossings obtained previously for the GPP as analytic solutions of the Whittaker-Hill equation. These solutions characterize both the squeezing and the tunneling of atoms trapped in an optical superlattice and pave the way to unraveling their dynamics in analytic form.