Protocol for optically pumping AlH⁺ to a pure quantum state.

Area of Science:

• Molecular Physics
• Quantum Chemistry
• Laser Spectroscopy

Background:

• Preparing molecules in pure quantum states is crucial for precision measurements and quantum information applications.
• Trapped molecular ions like AlH+ offer a stable platform for studying fundamental physics.
• Achieving population in specific hyperfine states requires sophisticated state preparation techniques.

Purpose of the Study:

• To propose and simulate an optical pumping scheme for preparing trapped AlH+ molecules in a pure rovibronic ground state.
• To investigate the efficiency of rotational cooling and hyperfine state preparation using tailored laser fields.
• To explore the impact of an additional infrared laser on accelerating the cooling process.

Main Methods:

• Utilized linearly and circularly polarized laser fields for rotational cooling and hyperfine state preparation.
• Simulated population dynamics using rate equations, incorporating laser fields, blackbody radiation, and spontaneous emission.
• Computed new hyperfine constants for the A2Π excited state using Restricted Advanced Self-Consistent Field (RASSCF) wavefunctions.

Main Results:

• Achieved a population of 63% in the target hyperfine state after 68 μs with the proposed scheme.
• Demonstrated accelerated cooling with an additional infrared laser, reaching 95% population in 25 ms.
• Without the infrared laser, 95% population was reached in 1.2 s, highlighting the laser's effectiveness.

Conclusions:

• The proposed optical pumping scheme effectively prepares trapped AlH+ molecules in a pure rovibronic ground state.
• The inclusion of an infrared laser significantly enhances the speed of the cooling and state preparation process.
• This method provides a viable route for high-fidelity state preparation of molecular ions for future applications.