Vibrational Molecular Clock in a State-Insensitive Optical Lattice

Techniques originally developed for atomic clocks can be adapted to ultracold molecules, with applications ranging from quantum-state-controlled ultracold chemistry to searches for new physics. Here we present recent experimental results with a molecular lattice clock that is based on a frequency difference between two vibrational levels in the electronic ground state of strontium diatomic molecules. Such a clock allows us to test molecular QED, search for mass-dependent ``fifth-force'' interactions, and potentially probe the electron-to-proton mass ratio variations. The achieved quality factor for the molecular clock is $Q=8\times 10^{11}$. Trap-insensitive spectroscopy is crucial for extending coherent molecule-light interactions and achieving high $Q$’s. We have demonstrated a ``magic wavelength'' technique for molecules by manipulating the optical lattice frequency near narrow polarizability resonances. This technique allows us to increase the coherence time by over a thousandfold and to narrow the linewidth of a 30 THz vibrational transition initially to 30 Hz. Long coherence times of molecular state superpositions are critical not only for fundamental metrology but also for quantum information.