Ultracold 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. We present recent experimental results on the $^{88}Sr_2$ molecular clock which allows us to test molecular QED, search for mass-dependent “fifth-force” interactions, and potentially probe the electron-to-proton mass ratio variations. The oscillator of such a molecular clock consists of the frequency difference between two vibrational levels in the electronic ground state. The transition between the levels is driven by a pair of Raman lasers via an off-resonant excited state. We have achieved transitions from weakly bound to multiple deeply bound ground states. Trap-insensitive spectroscopy is crucial for extending coherent molecule-light interactions. We have demonstrated the “magic wavelength” technique for molecules by manipulating the optical lattice frequency near narrow polarizability resonances. This technique allows us to increase the coherence time a thousandfold and to narrow the ~30 THz vibrational transition initially to ~100 Hz. Long coherence times of molecular state superpositions are useful not only for fundamental metrology but also for quantum information.