arXiv:2511.16626

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

Olivier Grasdijk, Jakob Kastelic, Jianhui Li, Oskari Timgren, Konrad Wenz, Yang, Yuanhang, Zhou, Perry, D. Kawall, Tanya Zelevinsky, David P. DeMille

Published Nov 20, 2025• 0 citations

arXiv HTML PDF

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 $X\,^1Σ^+_0$ 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.

DOI: 10.48550/arxiv.2511.16626

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arXiv:2511.16626

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

Olivier Grasdijk, Jakob Kastelic, Jianhui Li, Oskari Timgren, Konrad Wenz, Yang, Yuanhang, Zhou, Perry, D. Kawall, Tanya Zelevinsky, David P. DeMille

Published Nov 20, 2025• 0 citations

arXiv HTML PDF

Abstract

\left|J,m_J=0\right\rangle

hyperfine sublevels of the

X\,^1Σ^+_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

J=1

at a local field of

173~\mathrm{V/cm}

, and the second transfers from

J=1

J=2

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

J=2

. These results demonstrate robust and high-fidelity preparation of specific rotational/hyperfine states in TlF.

DOI: 10.48550/arxiv.2511.16626

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arXiv:1001.4394Physical Review AJan 27, 20109 citations

Adiabatic passage of

^{205}

TlF with microwaves in a cryogenic beam

\left|J,m_J=0\right\rangle

hyperfine sublevels of the

X\,^1Σ^+_0

J=0

J=1

at a local field of

173~\mathrm{V/cm}

, and the second transfers from

J=1

J=2

110~\mathrm{V/cm}

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

J=2

. These results demonstrate robust and high-fidelity preparation of specific rotational/hyperfine states in TlF.

Rotational-hyperfine cooling of

^{205}

TlF in a cryogenic beam

The aim of CeNTREX (Cold Molecule Nuclear Time-Reversal Experiment) is to search for time-reversal symmetry violation in the thallium nucleus, by measuring the Schiff moment of

^{205}

Tl in the polar molecule thallium fluoride (TlF). CeNTREX uses a cryogenic beam of TlF with a rotational temperature of 6.3(2) K. This results in population spread over dozens of rotational and hyperfine sublevels of TlF, while only a single level is useful for the Schiff moment measurement. Here we present a protocol for cooling the rotational and hyperfine degrees of freedom in the CeNTREX beam, transferring the majority of the Boltzmann distribution into a single rotational and hyperfine sublevel by using a single ultraviolet laser and a pair of microwave beams. We achieve a factor of

20.1(4)

gain in the population of the

J=0

F=0

hyperfine sublevel of the TlF ground state.

{\mathit{D}}_{2}

line. An efficiency of more than 50% is observed for the

{\mathit{m}}_{\mathit{F}}

=+4\ensuremath{\rightarrow}

{\mathit{m}}_{\mathit{F}}

=-4 population transfer. The influence of other excited hyperfine levels on the transfer efficiency is pointed out. The feasibility of the technique with counterpropagating laser beams is also demonstrated.

The preparation of a sample of ultra cold caesium atoms in an

{m}_{F}=0

Zeeman sublevel of the

F=3

ground state is demonstrated, using cooling in an optical lattice and adiabatic passage. 97% of the atoms finally detected in the experiment populate the

{m}_{F}=0

sublevel at a temperature of

300\phantom{\rule{0.3em}{0ex}}\mathrm{nK}

. Microwave spectroscopy is used to measure the adiabatic transfer directly and its dependence on various experimental parameters. A theoretical model is provided to estimate the upper limit for the efficiency of adiabatic transfer in a multilevel system with nonresonant excitation. The results constitute significant progress towards constructing a caesium fountain frequency standard operating in the nK temperature range.

98%

for realistic parameters and including spontaneous emission. Even though our main focus is on cooling molecular states, the analysis of the different adiabatic methods has general features which can be applied to atomic systems.