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arXiv:1205.1876

Cavity-meidated collisionless sympathetic cooling of molecules with atoms

Guangjiong Dong, Chang Wang, Weiping Zhang

Published May 9, 2012• 0 citations
arXivHTMLPDF

Abstract

Cooling a range of molecules to ultracold temperatures (<1 mK) is a difficult but important challenge in molecular physics and chemistry. Collective cavity cooling of molecules is a promising method that does not rely on molecular energy level and thus can be applied to all molecules in principle. However, the initial lack of cold molecules leads to the difficulty in its experimental implementation. We show that efficient collective sympathetic cooling of molecules to sub-mK temperatures using a large ensemble of atoms within a cavity is feasible. This approach is a new type of sympathetic cooling which does not rely on direct collisions between atoms and molecules, but utilizes thermalization via their mutual interaction with a cavity field. Two important mechanisms are identified. This include: (1) giant enhancement of cavity optical field from the efficient scattering of the pump light by the atoms; (2) cavity-mediated collective interaction between the atoms and the molecules. We show an optimal cavity detuning for maximizing cooling, which is dependent on the atom and molecule numbers. We determine a threshold for the molecular pump strength and show that it is independent of molecule number when the number of atoms is much greater than the molecules. This can be reduced by orders of magnitude when compared to cavity cooling of single molecular species only. Using this new sympathetic cavity cooling technique, cooling molecules to sub-mK within a high-Q cavity could be within reach of experimental demonstration.

DOI
10.48550/arxiv.1205.1876

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Cooling a range of molecules to ultracold temperatures (<1 mK) is a difficult but important challenge in molecular physics and chemistry. Collective cavity cooling of molecules is a promising method that does not rely on molecular energy level and thus can be applied to all molecules in principle. However, the initial lack of cold molecules leads to the difficulty in its experimental implementation. We show that efficient collective sympathetic cooling of molecules to sub-mK temperatures using a large ensemble of atoms within a cavity is feasible. This approach is a new type of sympathetic cooling which does not rely on direct collisions between atoms and molecules, but utilizes thermalization via their mutual interaction with a cavity field. Two important mechanisms are identified. This include: (1) giant enhancement of cavity optical field from the efficient scattering of the pump light by the atoms; (2) cavity-mediated collective interaction between the atoms and the molecules. We show an optimal cavity detuning for maximizing cooling, which is dependent on the atom and molecule numbers. We determine a threshold for the molecular pump strength and show that it is independent of molecule number when the number of atoms is much greater than the molecules. This can be reduced by orders of magnitude when compared to cavity cooling of single molecular species only. Using this new sympathetic cavity cooling technique, cooling molecules to sub-mK within a high-Q cavity could be within reach of experimental demonstration.
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Inspired by the great success in laser cooling of atoms, scientists now want to create cold molecules to study their applications that have already realized for cold atoms. However, a simple extension of laser cooling techniques fails for molecules because complex energy structure of most molecules makes a closed multi-level system impossible. Buffer gas cooling is a general scheme that can produce cold paramagnetic molecules at temperatures of hundreds milikelvin (mK). The next requirement for this field to be successful is to develop new and complementary techniques that can break the mK bottleneck and produce a dense molecular samples in microkelvin (muK) region. In this report, we study a general optical cavity cooling scheme to cool molecular species from hundreds mK to muK temperature region.
We have studied theoretically and numerically the cooling of CN molecules in a high-finesse optical cavity and show that these molecules can be cooled from 100 mK temperatures to submillikelvin temperatures in less than 1 ms. We establish that the cooling time does not change significantly with molecular numbers and initial temperatures over a wide range. We have further studied the scaling of the system for extending the current results for hundreds of molecules to a very large molecular ensemble. The results indicate that a gas of 109 molecules can be cooled in the cavity by use of a far-off-resonant and high-intensity pump source. © 2007 The American Physical Society.
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