Ultracold Triatomic Molecules

Atoms and molecules are the microscopic building blocks of the world. Their behavior and interactions are governed by the theory of quantum mechanics, which describes at a fundamental level much of modern science and technology. However, advancing quantum science and technology in the second quantum revolution requires cooling to temperatures around one millionth of a degree above absolute zero.

Over the past several decades, powerful laser cooling techniques have been developed to reach these “ultracold” temperatures with atoms; in turn, a number of discoveries were made that shed light on the intricacies of quantum physics in complicated systems and led to the creation of a useful quantum computer. These techniques have more recently been extended to diatomic molecules (containing two atoms), but larger molecules (“polyatomic”) have so far eluded full quantum control.

Cooling polyatomic molecules will shed light on the quantum nature of chemical reactions and be a resource for yet even more powerful quantum simulation, which can lead to the development of new technological materials. In this project, Professor John Doyle and his research team of graduate and undergraduate students and postdoctoral researchers will use laser cooling to trap CaOH (calcium monohydroxide) molecules at ultracold temperatures and then study their collisions, which will shed light on the quantum physics underlying molecular interactions. The aim is to eventually build a quantum computer using single molecule arrays of CaOH molecules.

The experimental starting point of this work will be to cool and trap CaOH molecules in a magneto-optical trap (MOT). This will require scattering tens of thousands of optical photons from the molecules to remove energy and momentum, which is enabled by a careful understanding of the vibrational structure of CaOH developed recently by Professor Doyle and his research group.

Because polyatomic molecules like CaOH cannot scatter photons indefinitely, they will then be transferred into a conservative optical dipole trap (ODT) -- where they can be held for several seconds without being lost. There, they can also be sub-Doppler cooled to temperatures near 1μK. By loading approximately 104 molecules into the ODT, sufficient density should be obtained to study collisions between CaOH molecules.

After populating the molecules in an excited vibrational state and applying modest DC electric fields of ~1 kV/cm, it is expected that inelastic collisions will be effectively shielded, enabling evaporative cooling of triatomic molecules to even lower temperatures. The researchers additionally propose to load CaOH molecules into optical tweezers, which present an alternative route to collisional studies and could also be used to implement novel quantum simulation and computation schemes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.