Adiabatic passage of $^{205}$TlF with microwaves in a cryogenic beam

TL;DR

This paper demonstrates a microwave-driven adiabatic passage method for efficient, high-fidelity hyperfine state preparation in TlF molecules within a cryogenic beam, crucial for nuclear symmetry violation experiments.

Contribution

It introduces a robust two-stage adiabatic passage technique for precise hyperfine state transfer in TlF molecules, enhancing experimental control for fundamental physics tests.

Findings

Achieved over 97% total population transfer efficiency from J=0 to J=2.

Demonstrated robustness and high fidelity in state preparation.

Validated the method using laser-induced fluorescence measurements.

Abstract

We present a hyperfine-resolved state preparation scheme for thallium fluoride (TlF) molecules based on microwave-driven adiabatic passage (AP) in a spatially varying electric field. This method enables efficient and robust population transfer between selected $\left|J,m_J=0\right\rangle$ hyperfine sublevels of the $X\,^1\Sigma^+_0$ ground state in a cryogenic molecular beam, a key requirement for the CeNTREX search for nuclear time-reversal symmetry violation. Two sequential stages of AP are implemented. The first transfers population from $J=0$ to $J=1$ at a local field of $173~\mathrm{V/cm}$, and the second transfers from $J=1$ to $J=2$ at $110~\mathrm{V/cm}$. Transfer efficiencies are quantified through laser-induced fluorescence, and accounting for residual population in excited rotational levels after a prior stage of rotational cooling. We achieve state transfer efficiencies of $0.92(6)$ and $1.05(5)$ for the first and second states of AP, respectively. This corresponds to a total efficiency of $0.97(8)$ for population transfer from $J=0$ to $J=2$. These results demonstrate robust and high-fidelity preparation of specific rotational/hyperfine states in TlF.