Robust, fast, and efficient formation of stable tetratomic molecules from ultracold atoms via generalized stimulated Raman exact passage

TL;DR

The paper tackles the challenge of forming stable ultracold polyatomic (tetratomic) molecules by proposing a two-step approach: (i) a generalized nonlinear STIREP protocol to coherently convert ultracold atoms into tetratomic molecules, and (ii) a chainwise STIREP (C-STIREP) to transfer these molecules into a deeply bound ground state. The method leverages resonance-locking to suppress nonlinear phase effects and employs a two-angle parameterization to design the driving fields, achieving fast, robust, high-efficiency conversion. It then extends to a five-state chainwise model with adiabatic elimination, deriving a generalized resonance condition and constructing a four-field C-STIREP protocol that enables rapid ground-state transfer while mitigating population in short-lived intermediates. Numerical analyses demonstrate near-ideal conversion and high-fidelity ground-state transfer with substantial robustness to drive errors, highlighting a viable path to stable ultracold tetratomic molecules and potential extensions to larger polyatomic systems.

Abstract

The study of the conversion of ultracold atoms into molecules has long remained a hot topic in atomic, molecular, and optical physics. However, most prior research has focused on diatomic molecules, with relatively scarce exploration of polyatomic molecules. Here we propose a two-step strategy for the formation of stable ultracold tetratomic molecules. We first suggest a generalized nonlinear stimulated Raman exact passage (STIREP) technique for the coherent conversion of ultracold atoms to tetratomic molecules, which is subsequently followed by a chainwise-STIREP technique to transfer the resulting molecules into a sufficiently stable ground state. Through systematic numerical analysis, we demonstrate that the proposed two-step strategy holds great potential for the robust, fast, and efficient formation of stable ultracold tetratomic molecules.

Figures (8)

• Figure 1: (Color online) Schematic showing the coherent conversion from ultracold atoms to tetratomic molecules.
• Figure 2: (Color online) Rabi frequencies (left column) and populations (left column) as a function of $t$. Adopted Parameters: $\eta=0.96, \epsilon=0.2$.
• Figure 3: (Color online) (a) Rabi frequencies as functions of $t$ under the generalized STIREP and the STIRAP. $\chi=8.4437$; (b) Conversion efficiency as a function of $\eta_1$ and $\eta_2$ under the (upper surface) generalized STIREP and (lower surface) STIRAP protocols; (c) Conversion efficiency as a function of $T$ under the generalized STIREP; Parameters: $\gamma_m=10^{-1}/T$, $\gamma_t=10^{-4}/T$.
• Figure 4: (Color online) (a) Contour plot showing conversion efficiency versus $\delta T$ and $\delta\Omega_1$, where $\Omega_2$ is fixed at its ideal value without any deviations; (b) Contour plot showing conversion efficiency versus $\delta T$ and $\delta\Omega_2$, where $\Omega_1$ is fixed at its ideal value. Note that parameter deviations are implemented on the basis of the original parameters in Fig. \ref{['fig2']}.
• Figure 5: (Color online) A schematic of coherent population transfer from weakly- to deeply-bound molecules.