Quantum control in molecules
Prof. Hutzler, Nicholas R.
The fact that the universe is made out of matter currently has no explanation. All known physical processes would have created a universe with essentially equal amounts of matter and anti-matter, yet there is no free anti-matter to be found. This is very fortunate for us, since anti-matter and matter annihilate each other into photons! We don't know what particle or force resulted in a matter-dominated universe, but we do know that it violates a number of fundamental symmetries -- not just the symmetry between matter and anti-matter, but also symmetries that prevent certain symmetry-violating electromagnetic interactions. Searching for these interactions is a powerful way to search for new high-energy physics in a low-energy, table top setting, and it turns out that molecules have the highest sensitivity of any known system. The internal electromagnetic fields in molecules are around a million times larger than those that can be created in the lab, which leads to a direct amplification of these symmetry-violating electromagnetic interactions.
To realize the full benefits of molecules, we need to implement quantum control. If we can prepare the molecules in a coherent state, and let them evolve coherently for long periods of time, the signature of the symmetry-violating interaction will continue to build up during the entire evolution time, leading to significant gains. Quantum control with molecules is difficult due to their complex internal structure, but the payoffs make it worthwhile. By implementing modern control techniques, such as laser-cooling and trapping, the sensitivity of these experiments can increase by orders of magnitude.
Quantum control in molecules has many applications outside of searches for fundamental symmetry violation. For example, molecules have strong, long-range, anisotropic, and completely tunable interactions, which make them valuable tools for quantum information, quantum simulation of condensed matter systems, and studies of quantum many-body physics. Molecules can also undergo chemical reactions, which enables quantum-controlled chemistry. All of these exciting applications (and more!) rely on quantum control, and are behind the very rapid advances in molecular cooling and control over the past decade -- advances that we hope to continue driving here at Caltech.