Protocol for Optically Pumping AlH$^+$ to a Pure Quantum State

TL;DR

This paper presents a novel optical pumping method to prepare AlH$^+$ molecules in a specific pure quantum state, using broadband pulsed lasers and simulations to optimize population transfer.

Contribution

It introduces a new optical pumping scheme for AlH$^+$ molecules, including computed hyperfine constants and simulation of population dynamics for state preparation.

Findings

Population in target state reaches 63% after 68 μs with IR laser.

Population reaches 95% after 25 ms with IR laser.

Adding IR laser accelerates the cooling process.

Abstract

We propose an optical pumping scheme to prepare trapped $\mathrm{AlH}^+$ molecules in a pure state, the stretched hyperfine state $\lvert F=\frac{7}{2},\, m_F=\frac{7}{2}\rangle$ of the rovibronic ground manifold $\lvert \mathrm{X}^2\Sigma^+,\, v=0,\, N=0\rangle$. Our scheme utilizes linearly-polarized and circularly-polarized fields of a broadband pulsed laser to cool the rotational degree of freedom and drive the population to the hyperfine state, respectively. We simulate the population dynamics by solving a representative system of rate equations that accounts for the laser fields, blackbody radiation, and spontaneous emission. In order to model the hyperfine structure, new hyperfine constants of the $\mathrm{A}^2\Pi$ excited state were computed using a RASSCF wavefunction. We find that adding an infrared laser to drive the $1 \,-\; 0$ vibrational transition within the $ \mathrm{X}^2\Sigma^+$ manifold accelerates the cooling process. The results show that under optimum conditions, the population in the target state of the rovibronic ground manifold can reach 63 $\%$ after 68 $\mathrm{\mu}$s (330 ms) and 95 $\%$ after 25 ms (1.2 s) with (without) the infrared laser.