Quantum treatment of two-stage sub-Doppler laser cooling of magnesium atoms

TL;DR

This paper presents a quantum theoretical analysis of a two-stage sub-Doppler laser cooling method for magnesium atoms, aiming to achieve ultracold temperatures below 10 microkelvin, with implications for quantum metrology.

Contribution

It introduces a fully quantum treatment of magnesium laser cooling, including recoil effects, and compares results with semiclassical approaches, highlighting conditions for optimal ultracold atom production.

Findings

Quantum analysis reveals differences from semiclassical models.

Second cooling stage can lower kinetic energies more effectively.

Achieves large ultracold atom numbers below 10 microkelvin.

Abstract

The problem of deep laser cooling of $^{24}$Mg atoms is theoretically studied. We propose two-stage sub-Doppler cooling strategy using electro-dipole transition $3^3P_2$$\to$$3^3D_3$ ($\lambda$=383.9 nm). The first stage implies exploiting magneto-optical trap with $\sigma^+$ and $\sigma^-$ light beams, while the second one uses a lin$\perp$lin molasses. We focus on achieving large number of ultracold atoms (T$_{eff}$ < 10 $\mu$K) in a cold atomic cloud. The calculations have been done out of many widely used approximations and based on quantum treatment with taking full account of recoil effect. Steady-state average kinetic energies and linear momentum distributions of cold atoms are analysed for various light-field intensities and frequency detunings. The results of conducted quantum analysis have revealed noticeable differences from results of semiclassical approach based on the Fokker-Planck equation. At certain conditions the second cooling stage can provide sufficiently lower kinetic energies of atomic cloud as well as increased fraction of ultracold atoms than the first one. We hope that the obtained results can assist overcoming current experimental problems in deep cooling of $^{24}$Mg atoms by means of laser fields. Cold magnesium atoms, being cooled in large number down to several microkelvins, have certain interest, for example, in quantum metrology.