Laser Cooling of Complex Polyatomics

Research Overview

The goal of this experiment is to develop techniques to bring polyatomic molecules into the ultracold regime using direct cooling. The use of laser radiation to control and cool external and internal degrees of freedom has revolutionized atomic, molecular, and optical physics. The powerful techniques of laser cooling and trapping using light scattering forces for atoms led to breakthroughs in both fundamental and applied sciences, including detailed studies of diverse degenerate quantum gases [1,2], creation of novel frequency standards [3], and precision measurements of fundamental constants [4,5]. Polyatomic molecules are more difficult to manipulate than atoms and diatomic molecules because they possess additional rotational and vibrational degrees of freedom. Partially because of their increased complexity, cold dense samples of molecules with three or more atoms offer unique capabilities for exploring interdisciplinary frontiers in physics, chemistry and even biology. Precise control over polyatomic molecules could lead to applications in astrophysics [6], quantum simulation [7] and computation [8], fundamental physics [9,10], and chemistry [11]. Study of parity violation in biomolecular chirality [12]—which plays a fundamental role in molecular biology [13]—necessarily requires polyatomic molecules.

Our approach starts with buffer gas cooling[14-16], a technique that dramatically reduces the number of internal rotational and vibrational states by thermalizing a sample of molecules with He gas at ~1K. This initial cooling step is critical for working with molecules to limit the number of quantum states that have significant population. We are now working to adapt the laser cooling techniques that were so successful with atoms to work on molecular samples. While atomic species have selection rules that limit the number of states populated by spontaneous decay, Molecules have selection rules for electronic and rotational degrees of freedom but not vibrational degrees of freedom. Therefore, the major complication with molecules is branching to higher vibrational states outside of the cycling transition.

Motivated the recent success laser cooling and magneto-optical trapping diatomic molecules [16-26] and with insights gained in efforts underway in our own lab we have successfully extended sub-Doppler cooling techniques to polyatomic molecules.

We are currently pushing in two directions :

1. Extension of the bichromatic force to molecules. The bichromatic force relies on coherent control of molecular populations to exert a force on the molecules without scattering photons. This could have dramatic results for laser cooling of molecules because it could dramatically limit branching to higher vibrational states.
2. Extension of laser cooling to larger molecules. We have demonstrated that magnetically induced Sisyphus cooling works for SrOH, but increasing the size of the molecule and thus the complexity

People

We are looking for interested students to join this experiment

Please contact one of the graduate students for more information.

Grad Students

• Ivan Kozyryev
• Louis Baum

Undergrads

• Alex Sedlack

Former Students and Postdocs

• Boerge Hemmerling - Now a postdoc working with Prof Haffner at UC Berkeley
• Kyle Matsuda - Now a grad student University of Colorado/JILA
• Peter Olson - Now a undergraduate at Washington University

Latest News

Proposal to Extend Laser Cooling to MOR molecules

Our proposal to extend laser cooling to MOR molecules has been accepted for publication in the special issue of Chem Phys Chem. Our work on SrOH has brought our attention that beyond triatomic molecules there is a class of larger molecules that also possess electronic transitions with short lifetimes and diagonal Franck-Condon factors which make them amenable to laser cooling.

Magnetically Assisted Sisyphus Laser Cooling of SrOH on arXiv

Our work on Sisyphus Laser Cooling of SrOH has been submitted to PRL. The preprint is available at arXiv:1603.02787. This demonstrated that dramatic cooling of molecular samples is possible with limited numbers of scattered photons. 1 dimensional laser cooling is an important step towards 3 dimensional laser cooling.

Radiation pressure force demonstrated on SrOH

Our demonstration of Radiation pressure force on SrOH has been published in the special issue of . This is a crucial step on the road towards laser cooling of polyatomic SrOH.

References

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