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Quantum Electronics and Laser Science Conference

Optical cavity cooling of a large ensemble of molecules

Yongkai Zhao, Weiping Lu, P. F. Barker, Guangjiong Dong

Published Jun 2, 2009• 0 citations
OpenAlex

Abstract

We study optical cooling of a large ensemble of particles. We derive a new scaling law with respect to particle number and show a high density molecular cloud are cooled from 10mK to 700µK.

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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 100mK100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}100mK temperatures to submillikelvin temperatures in less than 1ms1\phantom{\rule{0.3em}{0ex}}\mathrm{ms}1ms. 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 109molecules{10}^{9}\phantom{\rule{0.3em}{0ex}}\text{molecules}109molecules can be cooled in the cavity by use of a far-off-resonant and high-intensity pump source.
The ability to cool and trap atoms has revolutionized atomic and ultra-cold physics. Molecular physics is currently undergoing a similar transformation. This thesis aims to research a general cooling method that will be applicable to wide range of molecular and atomic species and other particles. We studied the dynamics of molecules in optical fields, focusing in particular on exploring the molecular self-organisation phenomena in optical cavities to cool molecular ensembles to sub-mK temperatures. Firstly, the general model of cavity cooling from atoms to molecules and the dynamics of a particle in a single cavity mode were discussed. We extended the existing cooling scheme for two-level atoms to an ensemble of multi-level molecules. Then we studied the spatial dynamics of molecules in the new parameter conditions, focusing in particular on exploring the molecular self-organisation phenomena in optical cavities to cool molecular ensembles to sub-mK temperatures. The scheme complements well with our present experimental work on the deceleration and focusing of cold molecules and can extend our present capability to simultaneously cool and trap a large cold molecular ensemble. For simulation of a large ensemble of molecules, we proposed a new statistical model based on the Boltzmann equation beside the traditional discrete model and studied two solution methods. The comparison of the theory and numerical simulations between discrete model and statistical model showed a good agreement, which validated this new model. We then explored the scaling laws with a view to the self-organization and cooling of a large ensemble of species. We studied the cooling of a CN molecular cloud of the density 10/cm, with an initial temperature at 10 mK in an optical cavity. We found that more than a third of the molecules are stably trapped by the intracavity field and the final temperature is below 1mK. We discussed the scaling laws in the case when a large ensemble of species is involved. Finally we argue that cavity cooling using a far
We present an investigation of the dynamics of centre-of-mass of a neutral particle cloud in a cavity pumped by an optical field. We derive an expression for the pump threshold for spatial self-organization of the particles and analyze its scaling laws in terms of the system parameters. Using a newly developed statistical model, we simulate the dynamics of the particles and numerically obtain the scaling laws. We show good agreement between the analytic formulae and simulations. We further use the scaling relation to discuss the operating conditions for cavity cooling a large ensemble of particles. Finally, we study cavity cooling of an ensemble of molecules with an initial temperature of around 10 mK. We show that 35% of the molecules are trapped by the optical field intensity in the cavity and a final temperature below 1 mK is reached.
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.
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.