arXiv:2512.17653 · Physical Review A

$Λ$-Enhanced Gray Molasses Cooling of $^{85}$Rb Atoms in Tweezers Using the D$_2$ Line

Deon Janse van Rensburg, Rogier Venderbosch, Yuri van der Werf, Jesus del Pozo Mellado, Marijn Venderbosch, Rianne Lous, Edgar Vredenbregt, Servaas Kokkelmans

physics.atom-phquant-phSubmitted Dec 19, 2025• Announced Dec 22, 2025• 0 citations

arXiv HTML PDF

Abstract

We demonstrate the implementation of $Λ$-enhanced gray molasses cooling on the D$_2$ line of $^{85}$Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2) $μ$K compared to red-detuned polarization gradient cooling, and consequently extends the $T_2^*$ coherence time of the hyperfine clock qubit by a factor of 1.5. The method is alignment-free and can be readily implemented on laser beams used for magneto-optical trapping, as it only requires frequency and phase modulation control. Our experimental observations are corroborated by a numerical model based on a semi-classical force approach extended to a four-level system, including two hyperfine states of the upper manifold that are 120 MHz apart.

Journal reference: Phys. Rev. A 113, 033123 (2026)
DOI: 10.1103/tyxj-hb4l
Comments: 10 pages, 6 figures

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arXiv:2512.17653 · Physical Review A

$Λ$ -Enhanced Gray Molasses Cooling of $^{85}$ Rb Atoms in Tweezers Using the D $_2$ Line$Λ$-Enhanced Gray Molasses Cooling of $^{85}$Rb Atoms in Tweezers Using the D$_2$ Line

Deon Janse van Rensburg, Rogier Venderbosch, Yuri van der Werf, Jesus del Pozo Mellado, Marijn Venderbosch, Rianne Lous, Edgar Vredenbregt, Servaas Kokkelmans

physics.atom-phquant-phSubmitted Dec 19, 2025• Announced Dec 22, 2025• 0 citations

arXiv HTML PDF

Abstract

We demonstrate the implementation of

Λ

-enhanced gray molasses cooling on the D

_2

line of

^{85}

Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2)

μ

K compared to red-detuned polarization gradient cooling, and consequently extends the

T_2^*

coherence time of the hyperfine clock qubit by a factor of 1.5. The method is alignment-free and can be readily implemented on laser beams used for magneto-optical trapping, as it only requires frequency and phase modulation control. Our experimental observations are corroborated by a numerical model based on a semi-classical force approach extended to a four-level system, including two hyperfine states of the upper manifold that are 120 MHz apart.

Journal reference: Phys. Rev. A 113, 033123 (2026)
DOI: 10.1103/tyxj-hb4l
Comments: 10 pages, 6 figures

Related papers

Λ -enhanced gray-molasses cooling of cesium atoms on the D2 line

Ya-Fen Hsiao, Y.-J. Lin, Ying-Cheng Chen

We present a systematic study of the $\mathrm{\ensuremath{\Lambda}}$-enhanced gray molasses cooling ($\mathrm{\ensuremath{\Lambda}}$-GMC) of cesium atoms on the ${D}_{2}$ transition. Due to the large splitting in the excited hyperfine transitions of the cesium ${D}_{2}$ line, it is relatively simple to implement the $\mathrm{\ensuremath{\Lambda}}$-GMC with a suitable frequency control of the trapping and repumping lasers of the magneto-optical trap (MOT). We achieve a temperature of $1.7\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{K}$ with $3.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms. The phase space density of atoms is $1.43\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Compared to the condition with a bare MOT or a MOT with gray-molasses cooling without $\mathrm{\ensuremath{\Lambda}}$ enhancement, there is an increase in the phase space density by a factor of more than ${10}^{3}$ and 10, respectively.We present a systematic study of the $\mathrm{\ensuremath{\Lambda}}$-enhanced gray molasses cooling ($\mathrm{\ensuremath{\Lambda}}$-GMC) of cesium atoms on the ${D}_{2}$ transition. Due to the large splitting in the excited hyperfine transitions of the cesium ${D}_{2}$ line, it is relatively simple to implement the $\mathrm{\ensuremath{\Lambda}}$-GMC with a suitable frequency control of the trapping and repumping lasers of the magneto-optical trap (MOT). We achieve a temperature of $1.7\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{K}$ with $3.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms. The phase space density of atoms is $1.43\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Compared to the condition with a bare MOT or a MOT with gray-molasses cooling without $\mathrm{\ensuremath{\Lambda}}$ enhancement, there is an increase in the phase space density by a factor of more than ${10}^{3}$ and 10, respectively.

arXiv:1807.05745Physical Review ASep 28, 201820 citations

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Gray molasses is a powerful tool for sub-Doppler laser cooling of atoms to low temperatures. For alkaline atoms, this technique is commonly implemented with cooling lasers which are blue-detuned from either the D 1 or D 2 line. Here we show that efficient gray molasses can be implemented on the D 2 line of 40 K with red -detuned lasers. We obtained temperatures of , which enables direct loading of atoms from a magneto-optical trap into an optical dipole trap. We support our findings by a one-dimensional model and three-dimensional numerical simulations of the optical Bloch equations which qualitatively reproduce the experimentally observed cooling effects.Gray molasses is a powerful tool for sub-Doppler laser cooling of atoms to low temperatures. For alkaline atoms, this technique is commonly implemented with cooling lasers which are blue-detuned from either the D 1 or D 2 line. Here we show that efficient gray molasses can be implemented on the D 2 line of 40 K with red -detuned lasers. We obtained temperatures of , which enables direct loading of atoms from a magneto-optical trap into an optical dipole trap. We support our findings by a one-dimensional model and three-dimensional numerical simulations of the optical Bloch equations which qualitatively reproduce the experimentally observed cooling effects.

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Andrew T. Grier, Igor Ferrier-Barbut, Benno S. Rem +4 more

Following the bichromatic sub-Doppler cooling scheme on the ${D}_{1}$ line of ${}^{40}$ K recently demonstrated in Fernandes et al. [Europhys. Lett. 100, 63001 (2012)], we introduce a similar technique for ${}^{7}$ Li atoms and obtain temperatures of $60\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ while capturing all of the $5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified $\ensuremath{\Lambda}$-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of $\ensuremath{\sim}$${10}^{\ensuremath{-}5}$. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.Following the bichromatic sub-Doppler cooling scheme on the ${D}_{1}$ line of ${}^{40}$K recently demonstrated in Fernandes et al. [Europhys. Lett. 100, 63001 (2012)], we introduce a similar technique for ${}^{7}$Li atoms and obtain temperatures of $60\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ while capturing all of the $5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified $\ensuremath{\Lambda}$-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of $\ensuremath{\sim}$${10}^{\ensuremath{-}5}$. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.

arXiv:1304.6971Physical Review AJun 12, 2013132 citations

$Λ$ -enhanced gray molasses in a tetrahedral laser beam geometry

Daniel S. Barker, Eric B. Norrgard, Nikolai N. Klimov +3 more

We report observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2) % of the lithium atoms from a grating magneto-optical trap into $Λ$ -enhanced $D_1$ gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) $μ$ K and an axial temperature of 23(3) $μ$ K. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.We report observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2) % of the lithium atoms from a grating magneto-optical trap into $Λ$-enhanced $D_1$ gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) $μ$K and an axial temperature of 23(3) $μ$K. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.

arXiv:2110.03064Oct 6, 20210 citations

Λ-enhanced gray molasses in a tetrahedral laser beam geometry

D. S. Barker, Eric B. Norrgard, N. N. Klimov +3 more

We report the observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2)% of the lithium atoms from a grating magneto-optical trap into Λ-enhanced D 1 gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) μK and an axial temperature of 23(3) μK. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.We report the observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2)% of the lithium atoms from a grating magneto-optical trap into Λ-enhanced D 1 gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) μK and an axial temperature of 23(3) μK. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.

Optics ExpressFeb 28, 202211 citations

\Lambda-enhanced Sub-Doppler Cooling of Lithium Atoms in D1 Gray Molasses

Andrew T. Grier, Igor Ferrier-Barbut, Benno S. Rem +4 more

Following the bichromatic sub-Doppler cooling scheme on the D1-line of 40K recently demonstrated in (Fernandes et al. 2012), we introduce a similar technique for 7Li atoms and obtain temperatures of 60 uK while capturing all of the 5x10^8 atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified, \Lambda-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of ~10^-5. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.Following the bichromatic sub-Doppler cooling scheme on the D1-line of 40K recently demonstrated in (Fernandes et al. 2012), we introduce a similar technique for 7Li atoms and obtain temperatures of 60 uK while capturing all of the 5x10^8 atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified, \Lambda-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of ~10^-5. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.

Apr 25, 20130 citations

Λ

-Enhanced Gray Molasses Cooling of

^{85}

Rb Atoms in Tweezers Using the D

_2

Line

We demonstrate the implementation of

Λ

-enhanced gray molasses cooling on the D

_2

line of

^{85}

Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2)

μ

K compared to red-detuned polarization gradient cooling, and consequently extends the

T_2^*

We present a systematic study of the $\mathrm{\ensuremath{\Lambda}}$-enhanced gray molasses cooling ($\mathrm{\ensuremath{\Lambda}}$-GMC) of cesium atoms on the

{D}_{2}

transition. Due to the large splitting in the excited hyperfine transitions of the cesium

{D}_{2}

line, it is relatively simple to implement the $\mathrm{\ensuremath{\Lambda}}$-GMC with a suitable frequency control of the trapping and repumping lasers of the magneto-optical trap (MOT). We achieve a temperature of $1.7\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{K}$ with $3.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms. The phase space density of atoms is $1.43\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Compared to the condition with a bare MOT or a MOT with gray-molasses cooling without $\mathrm{\ensuremath{\Lambda}}$ enhancement, there is an increase in the phase space density by a factor of more than

{10}^{3}

and 10, respectively.

Sub-Doppler laser cooling of40K with Raman gray molasses on the

{D}_{2}

line

Following the bichromatic sub-Doppler cooling scheme on the

{D}_{1}

line of

{}^{40}

K recently demonstrated in Fernandes et al. [Europhys. Lett. 100, 63001 (2012)], we introduce a similar technique for

{}^{7}

Li atoms and obtain temperatures of $60\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ while capturing all of the $5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified $\ensuremath{\Lambda}$-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of $\ensuremath{\sim}$${10}^{\ensuremath{-}5}$. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.

Λ

-enhanced

D_1

gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9)

μ

K and an axial temperature of 23(3)

μ

K. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.