Exploiting SU(N ) dynamical symmetry for rovibronic stabilization of a weakly bound diatomic molecule

TL;DR

This paper introduces a multilevel laser-driven scheme leveraging SU(N) symmetry to efficiently transfer population between rovibronic states in diatomic molecules, demonstrated on KRb for rapid ground state stabilization.

Contribution

It develops an analytical, spin-mapping approach for coherent rovibronic population transfer using weak laser pulses, applicable to complex molecular systems.

Findings

Achieved full population transfer in about 1 ns for KRb molecule

Demonstrated the scheme's effectiveness with a chain of seven rovibronic states

Provided an analytical formula for state populations using SU(N) symmetry

Abstract

We propose a multilevel scheme to coherently transfer the population of a diatomic molecule from a rovibrational level to a target rovibrational level of the same electronic state or another. It involves a linear chain of N rovibrational levels alternating between the initial electronic state and a second electronic state, conveniently selected according to the dipole couplings between consecutive levels. A set of N - 1 simultaneous weak laser $\pi$ pulses, with simple analytical shapes, each in resonance between two neighbors of the chain, transfers the population from the initial rovibronic state gradually and consecutively through the chain, until at the end of the process it resides in the target rovibronic state, as in a kind of ping-pong game between the two electronic states. Using the partial-wave expansion of the molecular wave function, vibrational bases within the J manifolds of each electronic state, and the rotating-wave approximation (RWA), we map the radial Hamiltonian to the one of a spin s = (N - 1)/2 under a static magnetic field, providing an analytical formula for the populations of the linked states. As an illustration, we apply the scheme to the stabilization into the absolute ground state of a KRb molecule initially in the high-lying $\upsilon$ = 75, J = 6 level of the ground electronic state $X^{1}\Sigma^{+}$. With a chain of seven rovibronic states, three of them belonging to the excited $A^{1}\Sigma^{+}$ electronic state, and pulses of 0.4 ns of duration, the population is fully transferred into the target state in about 1 ns.