Protocol for optically pumping AlH+ to a pure quantum state

Abstract

We propose an optical pumping scheme to prepare trapped AlH⁺ molecules in a pure state, the stretched hyperfine state of the rovibronic ground manifold |X²Σ⁺, v = 0, N = 0 〉. 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 A²Π excited state were computed using a RASSCF wavefunction. We find that adding an infrared laser to drive the 1–0 vibrational transition within the X²Σ⁺ manifold accelerates the cooling process. The results show that, under optimal conditions, the population in the target state of the rovibronic ground manifold can reach 63% after 68 μs (330 ms) and 95% after 25 ms (1.2 s) with (without) the infrared laser.