A Zeeman slower for diatomic molecules

We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the one-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. We experimentally demonstrate our method in an atomic testbed and show an enhancement of flux below v = 35 m s −1 by a factor of ≈20 compared to white light slowing. 3D Monte Carlo simulations performed to model the experiment show excellent agreement. We apply the same simulations to the prototype molecule 88 Sr 19 F and expect 15% of the initial flux to be continuously compressed in a narrow velocity window at around 10 m s −1 . This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles.We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the one-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. We experimentally demonstrate our method in an atomic testbed and show an enhancement of flux below v = 35 m s −1 by a factor of ≈20 compared to white light slowing. 3D Monte Carlo simulations performed to model the experiment show excellent agreement. We apply the same simulations to the prototype molecule 88 Sr 19 F and expect 15% of the initial flux to be continuously compressed in a narrow velocity window at around 10 m s −1 . This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles.

arXiv:1712.05157New Journal of PhysicsMar 27, 201832 citations

A Zeeman slower for molecules

Kaebert, Paul

Cold molecules are an invaluable tool for modern physics. Cold atoms have already revolutionized precision metrology, allowed for spectacular findings in quantum physics and opened the door for the creation and observation of novel states of matter. Cold molecules bring with them additional degrees of freedom which give rise to unique properties that enable new kinds of experiments. For these experiments it is of vital importance to start with a sufficiently large number of cold molecules. There are multiple paths for the slowing and cooling of atoms and most of the slowing techniques utilizing lasers for direct cooling have been transferred to the molecular case with its specific requirements. The Zeeman slowing technique is advantageous for loading a trap with cold particles but had not yet been transferred from atoms to the molecular case. In this thesis I will show the first realization of the Zeeman slowing technique for diatomic molecules. This thesis will discuss several preparatory steps: Our group has had some ideas to collimate the molecular beam with a conical nozzle outlet at the buffer gas cell which I investigated on potassium atoms generated by the ablation of 39K35Cl inside the buffer gas cell. I also realized a fluorescence spectroscopy of the |XΣ1/2, N = 1, v = 0⟩ → |AΠ1/2, N = 0, v = 0⟩ transition in magnetic fields up to 300 G and confirmed simulations regarding our two laser cycling scheme in the Paschen-Back regime by measuring the scattering rate of light on one molecule. Finally, I created pre-cooled 40Ca19F with a forward velocity of around 150 m s−1 from a 40Ca19F2 target with laser ablation inside a cryogenic buffer gas cell. With the Zeeman slowing technique I slowed the molecules down to 25 m s−1, a velocity where trapping can be possible. I have also shown the characteristic compression into specific velocity classes for not yet trappable velocities. Together these two findings demonstrate that molecular Zeeman slowing is possible and a real promising tool for future experiments.Cold molecules are an invaluable tool for modern physics. Cold atoms have already revolutionized precision metrology, allowed for spectacular findings in quantum physics and opened the door for the creation and observation of novel states of matter. Cold molecules bring with them additional degrees of freedom which give rise to unique properties that enable new kinds of experiments. For these experiments it is of vital importance to start with a sufficiently large number of cold molecules. There are multiple paths for the slowing and cooling of atoms and most of the slowing techniques utilizing lasers for direct cooling have been transferred to the molecular case with its specific requirements. The Zeeman slowing technique is advantageous for loading a trap with cold particles but had not yet been transferred from atoms to the molecular case. In this thesis I will show the first realization of the Zeeman slowing technique for diatomic molecules. This thesis will discuss several preparatory steps: Our group has had some ideas to collimate the molecular beam with a conical nozzle outlet at the buffer gas cell which I investigated on potassium atoms generated by the ablation of 39K35Cl inside the buffer gas cell. I also realized a fluorescence spectroscopy of the |XΣ1/2, N = 1, v = 0⟩ → |AΠ1/2, N = 0, v = 0⟩ transition in magnetic fields up to 300 G and confirmed simulations regarding our two laser cycling scheme in the Paschen-Back regime by measuring the scattering rate of light on one molecule. Finally, I created pre-cooled 40Ca19F with a forward velocity of around 150 m s−1 from a 40Ca19F2 target with laser ablation inside a cryogenic buffer gas cell. With the Zeeman slowing technique I slowed the molecules down to 25 m s−1, a velocity where trapping can be possible. I have also shown the characteristic compression into specific velocity classes for not yet trappable velocities. Together these two findings demonstrate that molecular Zeeman slowing is possible and a real promising tool for future experiments.

Jan 1, 20250 citations

Improvements on type-II Zeeman slowing of molecules through polarization selectivity

Qian Liang, Wenhao Bu, Yuhe Zhang +2 more

We propose a general Zeeman slower scheme applicable to the majority of the laser-coolable molecules. Different from previous schemes, we apply a careful modulation on the repump laser and guarantee the velocity selectivity through the polarization selection rules. Only atoms or molecules with the right velocity will be laser slowed. Such a scheme is more feasible for molecules with complex energy structures. We apply this scheme for molecules with a large Land\'e $g$ factor of the excited states, i.e., ${g}_{e}>0.1$ , and polyatomic molecules with one-dimensional numerical simulations. The results show a better slowing efficiency with about 62% of the BaF molecules and 99% of the SrOH molecules being successfully slowed down to a velocity below $15\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$ without the consideration of transverse divergence.We propose a general Zeeman slower scheme applicable to the majority of the laser-coolable molecules. Different from previous schemes, we apply a careful modulation on the repump laser and guarantee the velocity selectivity through the polarization selection rules. Only atoms or molecules with the right velocity will be laser slowed. Such a scheme is more feasible for molecules with complex energy structures. We apply this scheme for molecules with a large Land\'e $g$ factor of the excited states, i.e., ${g}_{e}>0.1$, and polyatomic molecules with one-dimensional numerical simulations. The results show a better slowing efficiency with about 62% of the BaF molecules and 99% of the SrOH molecules being successfully slowed down to a velocity below $15\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$ without the consideration of transverse divergence.

arXiv:1906.10797Physical Review ANov 6, 201910 citations

Type-II Zeeman slowing: Characterization and comparison to conventional radiative beam-slowing schemes

M. Petzold, P. Kaebert, Philipp Gersema +4 more

We describe a Zeeman slowing method reported in [New J. Phys. 20, 042001 (2018)] and compare it to conventional radiative beam-slowing schemes. The scheme is designed to work on a type-II level structure, making it particularly attractive for radiative beam slowing of molecules. Working on the ${D}_{1}$ line of atomic $^{39}\mathrm{K}$ , we demonstrate efficient slowing of an atomic beam from $400\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ down to $35\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ with a final flux of $3.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. We give experimental details and compare our results to other established radiative slowing schemes in atomic and molecular physics. We find type-II Zeeman slowing to outperform white-light slowing commonly used in molecular beam slowing and to be comparably as efficient as traditional type-I Zeeman slowing being the standard beam-slowing technique in atomic physics.We describe a Zeeman slowing method reported in [New J. Phys. 20, 042001 (2018)] and compare it to conventional radiative beam-slowing schemes. The scheme is designed to work on a type-II level structure, making it particularly attractive for radiative beam slowing of molecules. Working on the ${D}_{1}$ line of atomic $^{39}\mathrm{K}$, we demonstrate efficient slowing of an atomic beam from $400\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ down to $35\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ with a final flux of $3.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. We give experimental details and compare our results to other established radiative slowing schemes in atomic and molecular physics. We find type-II Zeeman slowing to outperform white-light slowing commonly used in molecular beam slowing and to be comparably as efficient as traditional type-I Zeeman slowing being the standard beam-slowing technique in atomic physics.

arXiv:1811.10404Physical Review ADec 7, 20188 citations

Towards the mass production of slow, trappable molecules

Daniel McCarron

Abstract The Fast Track Communication by Petzold et al (2018 New J. Phys. 20 042001) demonstrates the first Zeeman slowing scheme for species with type-II optical cycling transitions. This new approach is directly applicable to those 2 Σ molecules that have recently been captured and cooled in molecular magneto-optical traps (MOTs) and has the potential to efficiently and continuously load these traps for the first time. This advance could produce molecular MOTs with populations comparable to their atomic counterparts and realize an ideal platform for a wide range of studies using large, dense samples of ultracold molecules.Abstract The Fast Track Communication by Petzold et al (2018 New J. Phys. 20 042001) demonstrates the first Zeeman slowing scheme for species with type-II optical cycling transitions. This new approach is directly applicable to those 2 Σ molecules that have recently been captured and cooled in molecular magneto-optical traps (MOTs) and has the potential to efficiently and continuously load these traps for the first time. This advance could produce molecular MOTs with populations comparable to their atomic counterparts and realize an ideal platform for a wide range of studies using large, dense samples of ultracold molecules.

New Journal of PhysicsMay 1, 20182 citations

Development of a magneto-optical trap for CaF molecules

Moritz Hambach

Laser cooling and trapping in a magneto-optical trap (MOT) have been essential to the success of cold atom physics in the last decades. Recently, the application of the same techniques to molecules has begun. The complexity of even a simple diatomic molecule makes laser cooling difficult, but promises new applications in many areas of research. In this thesis I describe the development of the first three-dimensional MOT of calcium fluoride (CaF) molecules. First, a cryogenic buffer gas source was set up, producing a pulsed beam of 9.3*10^10 molecules per steradian per pulse with forward velocities around 170 m/s. A similar source for very large molecules was set up during a 5 month internship at the University of Vienna. Next, the molecular pulse was slowed down to the capture velocity of a MOT using chirped laser slowing, resulting in about 7*10^5 CaF molecules passing through the typical MOT volume of 1 cm^3 at velocities of 15+-5 m/s. A new deceleration method, called Zeeman-Sisyphus deceleration, was also investigated. In this method molecules move through a spatially varying magnetic field and are optically pumped between low- and high-field seeking states in such as a way that they are always losing kinetic energy. The method promises to deliver more slow molecules because the molecules are guided transversely as they are decelerated. A small prototype was built and the optical pumping step was tested successfully. Finally, 7.6*10^3 CaF molecules were trapped in a MOT and cooled to a temperature of 8.5 mK. The radial trap frequency is 2 pi*130 Hz and the damping constant is beta=9.5*10^2 s^-1. The lifetime is about 100 ms and depends strongly on the scattering rate. This MOT is an an ideal starting point for a wide range of new experiments with ultracold molecules.Laser cooling and trapping in a magneto-optical trap (MOT) have been essential to the success of cold atom physics in the last decades. Recently, the application of the same techniques to molecules has begun. The complexity of even a simple diatomic molecule makes laser cooling difficult, but promises new applications in many areas of research. In this thesis I describe the development of the first three-dimensional MOT of calcium fluoride (CaF) molecules. First, a cryogenic buffer gas source was set up, producing a pulsed beam of 9.3*10^10 molecules per steradian per pulse with forward velocities around 170 m/s. A similar source for very large molecules was set up during a 5 month internship at the University of Vienna. Next, the molecular pulse was slowed down to the capture velocity of a MOT using chirped laser slowing, resulting in about 7*10^5 CaF molecules passing through the typical MOT volume of 1 cm^3 at velocities of 15+-5 m/s. A new deceleration method, called Zeeman-Sisyphus deceleration, was also investigated. In this method molecules move through a spatially varying magnetic field and are optically pumped between low- and high-field seeking states in such as a way that they are always losing kinetic energy. The method promises to deliver more slow molecules because the molecules are guided transversely as they are decelerated. A small prototype was built and the optical pumping step was tested successfully. Finally, 7.6*10^3 CaF molecules were trapped in a MOT and cooled to a temperature of 8.5 mK. The radial trap frequency is 2 pi*130 Hz and the damping constant is beta=9.5*10^2 s^-1. The lifetime is about 100 ms and depends strongly on the scattering rate. This MOT is an an ideal starting point for a wide range of new experiments with ultracold molecules.

Jul 1, 20170 citations

g

factor of the excited states, i.e.,

{g}_{e}>0.1

, and polyatomic molecules with one-dimensional numerical simulations. The results show a better slowing efficiency with about 62% of the BaF molecules and 99% of the SrOH molecules being successfully slowed down to a velocity below

15\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}

without the consideration of transverse divergence.

{D}_{1}

line of atomic

^{39}\mathrm{K}

, we demonstrate efficient slowing of an atomic beam from $400\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ down to $35\phantom{\rule{4pt}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ with a final flux of $3.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. We give experimental details and compare our results to other established radiative slowing schemes in atomic and molecular physics. We find type-II Zeeman slowing to outperform white-light slowing commonly used in molecular beam slowing and to be comparably as efficient as traditional type-I Zeeman slowing being the standard beam-slowing technique in atomic physics.