Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2508.15994 · Physical Review Research

Slowing YbF molecules using radiation pressure

M. Athanasakis-Kaklamanakis, G. Peng, S. Li, H. Septien-Gonzalez, Clément Debavelaere, A. D. White, S. Popa, Jongseok Lim, B. E. Sauer, Michael R. Tarbutt

Published Nov 10, 2025• 2 citations
arXivHTMLPDF

Abstract

We report radiation pressure slowing of YbF molecules to low velocity. In YbF, laser slowing is hindered by leaks out of the optical cycle attributed to low-lying metastable electronic states arising from inner-shell excitation. We bring this population back into the optical cycle once it has decayed to the electronic ground state using microwaves to couple the relevant rotational levels. We measure the scattering rate and closure of the optical cycle as repumps are added, and study the destabilization of dark states by a magnetic field and by polarization modulation, finding that both are helpful for maximizing the scattering rate. Starting from a beam with a mean speed of 80 m/s, and using frequency-broadened slowing light, we reduce the mean speed of the beam and produce a substantial flux in the low-velocity tail of the distribution. Slowing increases the fraction of molecules below 40 m/s from 0.4(1)% to 7.0(2)%, and the fraction below 30 m/s from zero to 3.2(1)%. The establishment of a nearly closed optical cycle and the production of molecules at low velocity are important steps toward trapping YbF molecules for future measurements of the electron's electric dipole moment.

DOI
10.1103/2vdb-c1f5

Related papers

Inner-shell excitation in the YbF molecule and its impact on laser cooling

Chi Zhang, Chaoqun Zhang, Lan Cheng +2 more

The YbF molecule is a sensitive system for measuring the electron’s electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these “4f hole” states lies below the A2Π1/2 excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as 10−5, can be a hindrance. Other 4f hole states lie very close to the A2Π1/2 state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the A2Π1/2 state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of the ground state, X2Σ+. We use electronic structure calculations to characterize the 4f hole states and the strengths of transitions between these states and the A2Π1/2 and X2Σ+ states. We identify a leak out of the cooling cycle with a branching ratio of roughly 5×10−4, dominated by the contribution of the ground state configuration in a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules with similar structure.

arXiv:2201.07871•Journal of Molecular Spectroscopy•Apr 1, 2022•18 citations

Understanding Inner-Shell Excitations in Molecules through Spectroscopy of the 4f Hole States of YbF

S. Popa, Sascha Schaller, André Fielicke +4 more

Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multiphoton ionization spectroscopy. We investigate the excited states of lowest energy, 8474, 9013, and 9090 cm−1 above the ground state, all corresponding to the configuration 4f136s2 F27/2 of the Yb+ ion. They are metastable, since they have no electric dipole allowed transitions to the ground state. We also characterize a state at 31 050 cm−1 that is easily excited from both the ground and metastable states, which makes it especially useful for this spectroscopic study. Finally, we study two states at 48 720 and 48 729 cm−1 , which are above the ionization limit and feature strong autoionizing resonances that prove useful for efficient detection of the molecules and for identifying the rotational quantum number of each line in the spectrum. We resolve the rotational structures of all these states and find that they can all be described by a very simple model based on Hund’s case (c). Our study provides information necessary for laser slowing and magneto-optical trapping of YbF, which is an important species for testing fundamental physics. We also consider whether the low-lying inner-shell states may themselves be useful as probes of the electron’s electric dipole moment or of varying fundamental constants, since they are long-lived states in a laser-coolable molecule featuring closely spaced levels of opposite parity. Published by the American Physical Society 2024

arXiv:2402.10692•Physical Review X•May 30, 2024•5 citations

Buffer gas cooling of YbF molecules

Sarah M. Skoff

This thesis reports on the production and characterisation of the first slow and cold beam of YbF molecules using buffer gas cooling. These molecules are being used to measure the electron’s electric dipole moment, and an intense source of slow-moving molecules is desirable for this experiment. The molecules are loaded into a buffer gas cell via laser ablation where they thermalise with cold helium buffer gas. They are then detected inside the cell using laser absorption imaging and spectroscopy on the X2Σ+→A2II1/2 transition. The formation, diffusion and thermalisation dynamics of the molecules inside the cell are studied. Measurements of laser absorption versus intensity reveal that saturation of the absorption is due to a competition between optical pumping into dark states and repopulation of the addressed level by inelastic and velocity-changing collisions. A beam of YbF molecules is extracted through an aperture in the buffer gas cell and characterised using laser induced fluorescence detection. Peak fluxes of 1010 molecules per steradian per pulse, in the rotational and vibrational ground state, are obtained. The translational and rotational temperatures are in equilibrium with the cell temperature of 4 K. The forward velocity of the pulses can be varied between 130 m/s and 200 m/s by changing the buffer gas pressure. This source is an order of magnitude brighter and more than three times slower than a supersonic source of YbF molecules and provides an excellent starting point for improving the measurement of the electron’s electric dipole moment and for deceleration and trapping experiments. In order to reduce the helium load on the vacuum system and to shorten the molecular pulses, a second set-up, delivering the buffer gas into an open copper cylinder in pulses rather than in a continuous flow,is characterised and shows promising first results.

•Sep 1, 2011•2 citations

A jet beam source of cold YbF radicals

Michael R. Tarbutt, J. J. Hudson, B. E. Sauer +4 more

We have developed a pulsed supersonic beam of slow, cold YbF molecular radicals with an intensity of 1.4 × 10 9 YbF molecules per steradian per pulse in the X 2 Σ + ( v = 0, N = 0) ground state. The translational and rotational temperatures of the beam are equal. The lowest temperature produced was 1.4 K and the slowest centre-of-mass velocity was 290 K. We show that YbF can be made either by ablating Yb metal into a fluorine-bearing carrier gas or by ablating solid precursors into a pure inert carrier gas. This source is suitable for injecting a molecule decelerator and for high-resolution laser-rf-double-resonance studies such as the measurement of the electron electric dipole moment.

Journal of Physics B Atomic Molecular and Optical Physics•Nov 27, 2002•58 citations

Slow molecular beams from a cryogenic buffer gas source

A. D. White, S. Popa, Jorge Mellado Muñoz +4 more

We study the properties of a cryogenic buffer gas source that uses a low-temperature two-stage buffer gas cell to produce very slow beams of ytterbium monofluoride molecules. The molecules are produced by laser ablation inside the cell and extracted into a beam by a flow of cold helium. We measure the flux and velocity distribution of the beam as a function of ablation energy, helium flow rate, cell temperature, and the size of the gap between the first and second stages of the cell. We also compare the velocity distributions from one-stage and two-stage cells. The one-stage cell emits a beam with a speed of about 82 m s − 1 and a translational temperature of 0.63 K. The slowest beams are obtained using the two-stage cell at the lowest achievable cell temperature of 1.8 K. This beam has a peak velocity of 56 m s − 1 and a flux of 9 × 10 9 ground-state molecules per steradian per pulse, with a substantial fraction at speeds below 40 m s − 1 . These slow molecules can be decelerated further by radiation pressure slowing and then captured in a magneto-optical trap. Published by the American Physical Society 2024

arXiv:2408.01862•Physical Review Research•Dec 3, 2024•7 citations

Optical pumping and laser slowing of a heavy molecule

Shuhua Deng, Shoukang Yang, Zixuan Zeng +1 more

Precision measurements of the electron’s electric dipole moment (eEDM) are critical for testing fundamental symmetries in particle physics, and heavy polar molecules—such as barium monofluoride (BaF)—have emerged as promising candidates for advancing the sensitivity. However, the achievement of a 3D magneto-optical trap (MOT) required slowing BaF molecules to near-zero velocity by scattering over 104 photons per molecule, demanding a quasi-cycling transition with minimal leakage. We present a detailed study of the leakage channels, including higher vibrational and rotational states. By combining microwave remixing with optical pumping of rotational and vibrational dark states, we reduced the total leakage fraction to 10−5. Using frequency-chirped laser slowing, we slowed a subset of buffer-gas-cooled BaF molecules from approximately 80 ms−1 to near-zero velocity, which is critical for efficient MOT loading. This work establishes the technical foundation for precision eEDM measurements using laser-cooled heavy molecules. Heavy polar molecules like BaF are key to boosting measurement sensitivity of the electron’s electric dipole moment (eEDM), but slowing heavy molecules to near-zero velocity for experiments is challenging. This study achieved reducing BaF’s total leakage fraction to 10−5 using microwave remixing and optical pumping and slowing buffer-gas-cooled BaF molecules from ~ 80 m/s to near-zero velocity.

arXiv:2512.24167•Communications Physics•Dec 2, 2025•0 citations
We report radiation pressure slowing of YbF molecules to low velocity. In YbF, laser slowing is hindered by leaks out of the optical cycle attributed to low-lying metastable electronic states arising from inner-shell excitation. We bring this population back into the optical cycle once it has decayed to the electronic ground state using microwaves to couple the relevant rotational levels. We measure the scattering rate and closure of the optical cycle as repumps are added, and study the destabilization of dark states by a magnetic field and by polarization modulation, finding that both are helpful for maximizing the scattering rate. Starting from a beam with a mean speed of 80 m/s, and using frequency-broadened slowing light, we reduce the mean speed of the beam and produce a substantial flux in the low-velocity tail of the distribution. Slowing increases the fraction of molecules below 40 m/s from 0.4(1)% to 7.0(2)%, and the fraction below 30 m/s from zero to 3.2(1)%. The establishment of a nearly closed optical cycle and the production of molecules at low velocity are important steps toward trapping YbF molecules for future measurements of the electron's electric dipole moment.
The YbF molecule is a sensitive system for measuring the electron’s electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these “4f hole” states lies below the A2Π1/2 excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as 10−5, can be a hindrance. Other 4f hole states lie very close to the A2Π1/2 state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the A2Π1/2 state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of the ground state, X2Σ+. We use electronic structure calculations to characterize the 4f hole states and the strengths of transitions between these states and the A2Π1/2 and X2Σ+ states. We identify a leak out of the cooling cycle with a branching ratio of roughly 5×10−4, dominated by the contribution of the ground state configuration in a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules with similar structure.
Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multiphoton ionization spectroscopy. We investigate the excited states of lowest energy, 8474, 9013, and 9090 cm−1 above the ground state, all corresponding to the configuration 4f136s2 F27/2 of the Yb+ ion. They are metastable, since they have no electric dipole allowed transitions to the ground state. We also characterize a state at 31 050 cm−1 that is easily excited from both the ground and metastable states, which makes it especially useful for this spectroscopic study. Finally, we study two states at 48 720 and 48 729 cm−1 , which are above the ionization limit and feature strong autoionizing resonances that prove useful for efficient detection of the molecules and for identifying the rotational quantum number of each line in the spectrum. We resolve the rotational structures of all these states and find that they can all be described by a very simple model based on Hund’s case (c). Our study provides information necessary for laser slowing and magneto-optical trapping of YbF, which is an important species for testing fundamental physics. We also consider whether the low-lying inner-shell states may themselves be useful as probes of the electron’s electric dipole moment or of varying fundamental constants, since they are long-lived states in a laser-coolable molecule featuring closely spaced levels of opposite parity. Published by the American Physical Society 2024
This thesis reports on the production and characterisation of the first slow and cold beam of YbF molecules using buffer gas cooling. These molecules are being used to measure the electron’s electric dipole moment, and an intense source of slow-moving molecules is desirable for this experiment. The molecules are loaded into a buffer gas cell via laser ablation where they thermalise with cold helium buffer gas. They are then detected inside the cell using laser absorption imaging and spectroscopy on the X2Σ+→A2II1/2 transition. The formation, diffusion and thermalisation dynamics of the molecules inside the cell are studied. Measurements of laser absorption versus intensity reveal that saturation of the absorption is due to a competition between optical pumping into dark states and repopulation of the addressed level by inelastic and velocity-changing collisions. A beam of YbF molecules is extracted through an aperture in the buffer gas cell and characterised using laser induced fluorescence detection. Peak fluxes of 1010 molecules per steradian per pulse, in the rotational and vibrational ground state, are obtained. The translational and rotational temperatures are in equilibrium with the cell temperature of 4 K. The forward velocity of the pulses can be varied between 130 m/s and 200 m/s by changing the buffer gas pressure. This source is an order of magnitude brighter and more than three times slower than a supersonic source of YbF molecules and provides an excellent starting point for improving the measurement of the electron’s electric dipole moment and for deceleration and trapping experiments. In order to reduce the helium load on the vacuum system and to shorten the molecular pulses, a second set-up, delivering the buffer gas into an open copper cylinder in pulses rather than in a continuous flow,is characterised and shows promising first results.
We have developed a pulsed supersonic beam of slow, cold YbF molecular radicals with an intensity of 1.4 × 10 9 YbF molecules per steradian per pulse in the X 2 Σ + ( v = 0, N = 0) ground state. The translational and rotational temperatures of the beam are equal. The lowest temperature produced was 1.4 K and the slowest centre-of-mass velocity was 290 K. We show that YbF can be made either by ablating Yb metal into a fluorine-bearing carrier gas or by ablating solid precursors into a pure inert carrier gas. This source is suitable for injecting a molecule decelerator and for high-resolution laser-rf-double-resonance studies such as the measurement of the electron electric dipole moment.
We study the properties of a cryogenic buffer gas source that uses a low-temperature two-stage buffer gas cell to produce very slow beams of ytterbium monofluoride molecules. The molecules are produced by laser ablation inside the cell and extracted into a beam by a flow of cold helium. We measure the flux and velocity distribution of the beam as a function of ablation energy, helium flow rate, cell temperature, and the size of the gap between the first and second stages of the cell. We also compare the velocity distributions from one-stage and two-stage cells. The one-stage cell emits a beam with a speed of about 82 m s − 1 and a translational temperature of 0.63 K. The slowest beams are obtained using the two-stage cell at the lowest achievable cell temperature of 1.8 K. This beam has a peak velocity of 56 m s − 1 and a flux of 9 × 10 9 ground-state molecules per steradian per pulse, with a substantial fraction at speeds below 40 m s − 1 . These slow molecules can be decelerated further by radiation pressure slowing and then captured in a magneto-optical trap. Published by the American Physical Society 2024
Precision measurements of the electron’s electric dipole moment (eEDM) are critical for testing fundamental symmetries in particle physics, and heavy polar molecules—such as barium monofluoride (BaF)—have emerged as promising candidates for advancing the sensitivity. However, the achievement of a 3D magneto-optical trap (MOT) required slowing BaF molecules to near-zero velocity by scattering over 104 photons per molecule, demanding a quasi-cycling transition with minimal leakage. We present a detailed study of the leakage channels, including higher vibrational and rotational states. By combining microwave remixing with optical pumping of rotational and vibrational dark states, we reduced the total leakage fraction to 10−5. Using frequency-chirped laser slowing, we slowed a subset of buffer-gas-cooled BaF molecules from approximately 80 ms−1 to near-zero velocity, which is critical for efficient MOT loading. This work establishes the technical foundation for precision eEDM measurements using laser-cooled heavy molecules. Heavy polar molecules like BaF are key to boosting measurement sensitivity of the electron’s electric dipole moment (eEDM), but slowing heavy molecules to near-zero velocity for experiments is challenging. This study achieved reducing BaF’s total leakage fraction to 10−5 using microwave remixing and optical pumping and slowing buffer-gas-cooled BaF molecules from ~ 80 m/s to near-zero velocity.