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Faraday Discussions

Sympathetic cooling by collisions with ultracold rare gas atoms, and recent progress in optical Stark deceleration

P. F. Barker, Simon M. Purcell, P. Douglas, Paolo Barletta, N. Coppendale, C. Maher-McWilliams, Jonathan Tennyson

Published Jan 1, 2009• 17 citations
Publisher

Abstract

We propose a general scheme for sympathetic cooling of molecules to microK temperatures on a timescale of seconds. Experimental parameters have been estimated from theory, which indicate the viability of the scheme. This method, which is particularly suited to optical Stark deceleration, utilises ultracold, laser cooled metastable rare gas atoms quenched to their ground state as collision partners to co-trapped molecular species within a deep optical trap (150 mK). We also describe the measurement of the role of laser-induced molecular alignment on the dipole force in optical Stark deceleration and outline progress towards the realisation of chirped optical Stark deceleration for producing slow molecular beams with mK energy spreads.

DOI
10.1039/b819079h

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This paper is published as part of Faraday Discussions volume 142: Cold and Ultracold Molecules

Dudley R. Herschbach, Sebastiaan Y. T. van de Meerakker, Gerard Meijer +4 more

Received 28th October 2008, Accepted 5th February 2009First published as an Advance Article on the web 28th May 2009DOI: 10.1039/b819079hWe propose a general scheme for sympathetic cooling of molecules to mKtemperatures on a timescale of seconds. Experimental parameters have beenestimated from theory, which indicate the viability of the scheme. This method,which is particularly suited to optical Stark deceleration, utilises ultracold, lasercooled metastable rare gas atoms quenched to their ground state as collisionpartnerstoco-trappedmolecular species within adeepopticaltrap(150mK). Wealso describe the measurement of the role of laser-induced molecular alignmenton the dipole force in optical Stark deceleration and outline progress towards therealisation of chirped optical Stark deceleration for producing slow molecularbeams with mK energy spreads.

•Jan 1, 2009•1 citation

Simulation of optical dipole trapping of cold CO molecules

Maurizio Verde

Ultracold matter offers a unique capability to reach the best high-precision spectroscopy measurements and leads to exciting perspectives in many different areas of science and technology. Molecules, thanks to their complex spectra, couple with a broader range of photons compared to atoms, so they are extremely attractive for fundamental science or to design new quantum technologies. However, to date, only a few molecular species have been brought to temperatures of the order of the microkelvin. This was done by laser cooling, a process that has been demonstrated only for species featuring an unpaired electron that does not participate to the chemical bond. \n \nA different approach, which is indifferent to the molecule electronic structure and thus potentially universal, is sympathetic cooling, where neutral molecules are cooled in a bath of ultracold atoms. However, inelastic collisions between molecules and the coolant is a major obstacle that has hindered the advances of this method thus far. Trapping the molecules in their absolute ground state would circumvent this problem or at least greatly simplify it. In this thesis we simulate the feasibility of an experiment in which metastable CO molecules are first slowed down to a few m/s with a microstructured Stark decelerator, then they are stopped by a strong DC electrical barrier and finally they are transferred irreversibly to their absolute ground state and captured in an optical trap. \nUnfortunately, the results of the simulations indicate that the total number of molecules that can be accumulated in the optical trap is rather low, far behind the observation threshold. Therefore, we concluded that other approaches to produce ultracold molecules must to be searched.

•Jan 1, 2020•0 citations

Creating ultracold molecules by collisions with ultracold rare-gas atoms in an optical trap

Paolo Barletta, Jonathan Tennyson, P. F. Barker

We study collisions of para-${\mathrm{H}}_{2}$ with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling ${\mathrm{H}}_{2}$ with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool ${\mathrm{H}}_{2}$ to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.

arXiv:0806.1196•Physical Review A•Nov 13, 2008•26 citations

Traveling-Wave Stark-Decelerated Molecular Beams for Cold Collision Experiments

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Research of cold and ultracold molecules is currently a burgeoning field in experimental and theoretical physics. New experimental techniques, involving an increasingly large set of molecule types under high levels of control, are currently opening up new avenues of research with a vast array of potential applications. From understanding the role of quantum mechanics in molecular scattering and cold chemistry, to testing the fundamental symmetries of nature and realizing quantum computing with dipolar molecular qubits, experiments are accessing regimes not dreamed of even a few years ago. Theoretical interest and computing capabilities are also at an all time high, spurred on by the possibility of creating ultracold dipolar gases as tunable realizations of strongly interacting quantum Hamiltonians, creating exotic phases of matter, and the investigation of controlling molecular interactions with applied electromagnetic fields.\nLess than a decade ago, cold molecule experiments had seemingly reached a technological plateau, being capable of creating moderate densities of 106-107 molecules/cm3 at temperatures of 10-100 mK. With many applications requiring colder temperatures and higher densities, the field was ripe for new advances. Today, via a plethora of methods such as direct molecular laser cooling, electro-optical cooling, magneto- and photo-association, and new molecular beam deceleration techniques, the field is just beginning to have the tools capable of producing truly interesting systems for study.\nThis work will discuss a couple of major steps taken in the direction of achieving scientific goals using cold molecules. The first experimental advancement discussed will be the development of a co-trap environment for studying interactions and collisions between ultracold atoms and Stark decelerated cold polar molecules. In this experiment, rubidium atoms are trapped using magnetic fields, and ammonia atoms are decelerated and trapped using electric fields. The two traps are spatially overlapped in order to investigate inter-species interactions. The co-trap environment provides exceedingly long interaction times, many orders of magnitude longer than typical beam-based interaction studies. As a result, it provides extremely high sensitivity to weak interaction mechanisms. The second experimental advancement discussed will be the development and construction of a new style of Stark decelerator, capable of producing much larger densities of cold molecules. This apparatus has the potential to expand the realm of possible experiments with chemically interesting species, and provide an unprecedented amount of control over molecular beams and traps. The gains haven't come easily though, as a new class of custom high-voltage amplifiers have needed to be developed. This part of the experiment alone took approximately two years of consistent effort to bring to fruition. After many years of development, this experiment is poised to come online, finally fulfilling its potential.

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Direct Monte Carlo simulation of the sympathetic cooling of trapped molecules by ultracold argon atoms

Paolo Barletta, Jonathan Tennyson, P. F. Barker

We demonstrate that cold molecules (H 2 and benzene) can be created at temperatures below 1 mK by sympathetic cooling with laser-cooled rare gas atoms on timescales of seconds. The thermalization process is studied using the direct simulation Monte Carlo (DSMC) method, which allows a detailed analysis of the atomic and molecular spatial and energy distributions as a function of time. As part of this study, ultracold elastic cross sections for Ar–Ar and Ar–C 6 H 6 are also calculated.

New Journal of Physics•Nov 2, 2010•18 citations

Laser cooling and trapping molecules

Daniel McCarron

Abstract The extension of laser cooling and trapping techniques from atoms to molecules is currently the subject of intense and growing interest. Molecular laser cooling and trapping offers a general technique applicable to a variety of molecules with different properties and internal structures and is well-suited to the growing list of proposed applications for ultracold molecules. The recent development of optical cycling schemes for specific molecular species now allow each molecule to scatter up to ∼10 6 photons. This has proven sufficient for multiple groups to laser cool and slow molecular beams and, notably, capture molecules in magneto-optical traps (MOTs) and cool them to ultracold temperatures. MOTs are the workhorse technique for atomic physics in the ultracold regime and today’s molecular MOTs represent a powerful starting point for the study and manipulation of ultracold molecular gases. This Topical Review presents a summary of the progress made in this new and emerging field.

Journal of Physics B Atomic Molecular and Optical Physics•Sep 7, 2018•72 citations
We propose a general scheme for sympathetic cooling of molecules to microK temperatures on a timescale of seconds. Experimental parameters have been estimated from theory, which indicate the viability of the scheme. This method, which is particularly suited to optical Stark deceleration, utilises ultracold, laser cooled metastable rare gas atoms quenched to their ground state as collision partners to co-trapped molecular species within a deep optical trap (150 mK). We also describe the measurement of the role of laser-induced molecular alignment on the dipole force in optical Stark deceleration and outline progress towards the realisation of chirped optical Stark deceleration for producing slow molecular beams with mK energy spreads.
Received 28th October 2008, Accepted 5th February 2009First published as an Advance Article on the web 28th May 2009DOI: 10.1039/b819079hWe propose a general scheme for sympathetic cooling of molecules to mKtemperatures on a timescale of seconds. Experimental parameters have beenestimated from theory, which indicate the viability of the scheme. This method,which is particularly suited to optical Stark deceleration, utilises ultracold, lasercooled metastable rare gas atoms quenched to their ground state as collisionpartnerstoco-trappedmolecular species within adeepopticaltrap(150mK). Wealso describe the measurement of the role of laser-induced molecular alignmenton the dipole force in optical Stark deceleration and outline progress towards therealisation of chirped optical Stark deceleration for producing slow molecularbeams with mK energy spreads.
Ultracold matter offers a unique capability to reach the best high-precision spectroscopy measurements and leads to exciting perspectives in many different areas of science and technology. Molecules, thanks to their complex spectra, couple with a broader range of photons compared to atoms, so they are extremely attractive for fundamental science or to design new quantum technologies. However, to date, only a few molecular species have been brought to temperatures of the order of the microkelvin. This was done by laser cooling, a process that has been demonstrated only for species featuring an unpaired electron that does not participate to the chemical bond. \n \nA different approach, which is indifferent to the molecule electronic structure and thus potentially universal, is sympathetic cooling, where neutral molecules are cooled in a bath of ultracold atoms. However, inelastic collisions between molecules and the coolant is a major obstacle that has hindered the advances of this method thus far. Trapping the molecules in their absolute ground state would circumvent this problem or at least greatly simplify it. In this thesis we simulate the feasibility of an experiment in which metastable CO molecules are first slowed down to a few m/s with a microstructured Stark decelerator, then they are stopped by a strong DC electrical barrier and finally they are transferred irreversibly to their absolute ground state and captured in an optical trap. \nUnfortunately, the results of the simulations indicate that the total number of molecules that can be accumulated in the optical trap is rather low, far behind the observation threshold. Therefore, we concluded that other approaches to produce ultracold molecules must to be searched.
We study collisions of para-H2{\mathrm{H}}_{2}H2​ with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling H2{\mathrm{H}}_{2}H2​ with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool H2{\mathrm{H}}_{2}H2​ to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.
Research of cold and ultracold molecules is currently a burgeoning field in experimental and theoretical physics. New experimental techniques, involving an increasingly large set of molecule types under high levels of control, are currently opening up new avenues of research with a vast array of potential applications. From understanding the role of quantum mechanics in molecular scattering and cold chemistry, to testing the fundamental symmetries of nature and realizing quantum computing with dipolar molecular qubits, experiments are accessing regimes not dreamed of even a few years ago. Theoretical interest and computing capabilities are also at an all time high, spurred on by the possibility of creating ultracold dipolar gases as tunable realizations of strongly interacting quantum Hamiltonians, creating exotic phases of matter, and the investigation of controlling molecular interactions with applied electromagnetic fields.\nLess than a decade ago, cold molecule experiments had seemingly reached a technological plateau, being capable of creating moderate densities of 106-107 molecules/cm3 at temperatures of 10-100 mK. With many applications requiring colder temperatures and higher densities, the field was ripe for new advances. Today, via a plethora of methods such as direct molecular laser cooling, electro-optical cooling, magneto- and photo-association, and new molecular beam deceleration techniques, the field is just beginning to have the tools capable of producing truly interesting systems for study.\nThis work will discuss a couple of major steps taken in the direction of achieving scientific goals using cold molecules. The first experimental advancement discussed will be the development of a co-trap environment for studying interactions and collisions between ultracold atoms and Stark decelerated cold polar molecules. In this experiment, rubidium atoms are trapped using magnetic fields, and ammonia atoms are decelerated and trapped using electric fields. The two traps are spatially overlapped in order to investigate inter-species interactions. The co-trap environment provides exceedingly long interaction times, many orders of magnitude longer than typical beam-based interaction studies. As a result, it provides extremely high sensitivity to weak interaction mechanisms. The second experimental advancement discussed will be the development and construction of a new style of Stark decelerator, capable of producing much larger densities of cold molecules. This apparatus has the potential to expand the realm of possible experiments with chemically interesting species, and provide an unprecedented amount of control over molecular beams and traps. The gains haven't come easily though, as a new class of custom high-voltage amplifiers have needed to be developed. This part of the experiment alone took approximately two years of consistent effort to bring to fruition. After many years of development, this experiment is poised to come online, finally fulfilling its potential.
Abstract The extension of laser cooling and trapping techniques from atoms to molecules is currently the subject of intense and growing interest. Molecular laser cooling and trapping offers a general technique applicable to a variety of molecules with different properties and internal structures and is well-suited to the growing list of proposed applications for ultracold molecules. The recent development of optical cycling schemes for specific molecular species now allow each molecule to scatter up to ∼10 6 photons. This has proven sufficient for multiple groups to laser cool and slow molecular beams and, notably, capture molecules in magneto-optical traps (MOTs) and cool them to ultracold temperatures. MOTs are the workhorse technique for atomic physics in the ultracold regime and today’s molecular MOTs represent a powerful starting point for the study and manipulation of ultracold molecular gases. This Topical Review presents a summary of the progress made in this new and emerging field.