Scaling up quantum-logic spectroscopy: prospects for precision measurements with polyatomic molecules

A revolution is underway in quantum control of molecular ions based on quantum-logic spectroscopy (QLS). In these experiments, a single molecular ion of interest is co-trapped together with a single atomic “logic” ion, which is used for sympathetic laser cooling of translational motion and quantum-logic readout of internal molecular states. Because this readout technique is non-destructive, it can be used to prepare pure vibrational, rotational, and hyperfine states of the molecule in a probabilistic but heralded fashion. A wide spectrum of coherent molecular transitions can be driven as two-photon stimulated-Raman-transitions using a single CW laser or femtosecond laser optical frequency comb. These sources can be hundreds of terahertz away from resonance with any molecular transitions, and no resonant lasers are required for the molecule. Thus, a broad class of molecular ion species can be studied in a single experimental apparatus using only a few lasers, unlocking new opportunities in physical chemistry, astro-chemistry, quantum information, quantum sensing, and searches for physics beyond the Standard Model. Thus far, however, these techniques have only been demonstrated on diatomic molecules.

This talk will present a new experiment being constructed at UCLA for QLS and precision measurements of polyatomic molecules. The primary obsticle to QLS of polyatomics is that many more states are populated by thermal radiation. We have designed a cryogenic vacuum chamber optimized to suppress the power spectral density of thermal radiation near molecular transition frequencies, and designed and simulated new machine-learning based QLS algorithms that reduce the number of measurements necessary for preparation of pure quantum states. The current status of the apparatus as well as plans for fundamental symmetry violation searches with polyatomic molecular ions will be discussed.