Polyatomic molecules offer the unique ability to probe CP-violation at the PeV scale through laser cooling and trapping combined with robust systematic error rejection.

Reaching the PeV Scale

Searches for the electron EDM depend on the ability to perform spin precession measurements with long interaction time and large numbers.  Both of these can be achieved with laser-cooled and trapped neutral polyatomic molecules, which also offer robust systematic error rejection techniques via internal co-magnetometer states.  The rapid advances in laser cooling of diatomic and polyatomic molecules have made such an experiment within reach, and will enable significant increases is sensitivity.  As an example, consider 106 heavy, eEDM-sensitive molecules in optical trap with 10 s coherence time.  After 1 week of integration, such an experiment will have sensitivity to CP-violating physics at the PeV scale.  This is beyond the reach of conceivable accelerators.  The ability to combine long coherence time, large numbers, internal co-magnetometers, and the ability to further enhance sensitivity via quantum control techniques is unique to polyatomic molecules.

Figure: Laser-cooled polyatomic molecules, optically trapped, with full quantum control.  Such a platform can be used to access new physics at the PeV scale.

Yb Polyatomics

The Yb atom is a powerful atom for precision measurement.  Its large mass induces highly relativistic motion of valence electrons near the heavy nucleus, making it a strong probe of CP violating physics.  YbF has been used to search for the eEDM, and the highly deformed nucleus of 173Yb makes it highly sensitive to hadronic CP-violation via a nuclear magnetic quadrupole moment (MQM).  The electronic structure of Yb is nearly identical to an alkaline earth atom, so Yb-bearing molecules are amenable to laser cooling.  

Figure: Levels and branching ratios in YbOH.  By exciting/repumping the levels indicated, we can slow, cool, and trap YbOH molecules for precision measurement.  From I. Kozyryev and N. R. Hutzler, Phys. Rev. Lett. 119, 133002 (2017)

A promising candidate is YbOH.  This molecule has a long-lived excited bending mode with parity doublets, making it highly polarizable and offering internal co-magnetometer states.  This molecule also has existing spectroscopy, which gives us a good starting point to make detailed spectroscopic measurements.

Figure: Preliminary spectroscopy and assignments in 174YbOH from the Steimle Group.

Symmetric top molecules such as YbOCH3 may offer even more advantages due to their very low-lying metastable states with parity doublets that are even more polarizable.

Figure: Symmetric tops such as YbOCH3 should maintain the ability to cycle photons for laser cooling while offering low-lying, fully-polarizable states corresponding to rotations of the CH3 group around the symmetry axis.

Want to know more?

Please be in touch if you have any questions!  Here is some suggested reading for more information as well.

Helpful websites:

Our proposal:
Precision Measurement of Time-Reversal Symmetry Violation with Laser-Cooled Polyatomic Molecules
I. Kozyryev and N. R. Hutzler

Some relevant references:

Laser Cooling of Optically Trapped Molecules
L. Anderegg, B. Augenbraun, Y. Bao, S. Burchesky, L. Cheuk, W. Ketterle, J. Doyle

Laser Cooled YbF Molecules for Measuring the Electron’s Electric Dipole Moment
J. Lim, J. R. Almond, M. A. Trigatzis, J. A. Devlin, N. J. Fitch, B. E. Sauer, M. R. Tarbutt, and E. A. Hinds

Sisyphus Laser Cooling of a Polyatomic Molecule
I. Kozyryev, L. Baum, K. Matsuda, B. L. Augenbraun, L. Anderegg, A. P. Sedlack, and J. M. Doyle

The visible laser excitation spectrum of YbOH: The A2Π-X2Σ+ transition
T. C. Melville and J. A. Coxon
J. Chem. Phys. 115, 6974 (2001)