Quantum control and high-precision metrology with ultracold optically-trapped molecules

Quantum state control and optical trapping of small ultracold molecules is at the forefront ofmodern quantum technologies. These capabilities expand the accessible science in quantumsimulation and computation, ultracold chemistry, as well as high-precision sensing andmetrology. Here we propose to develop a unique molecular system for metrology and precisesensing of interatomic forces. This system, a vibrational molecular lattice clock, is based onstrontium dimers that are photoassociated from microkelvin samples of strontium atoms andcoherently transferred to the absolute ground state. These van der Waals dimers are a uniquetype of ultracold molecules, with a completely spinless electronic ground state which is perfectlysuited for metrology and ab initio calculations. These molecules feature a series of narrowoptical transitions, greatl A keyaspect of metrological merit is the ability to place clock states into long-lived coherentsuperpositions. This requires magic trapping of the molecules, where both clock states see thesame trapping potential. We have demonstrated magic trapping by setting the optical latticefrequency near a narrow optical resonance, to tune the polarizability and therefore trap depth forthe lower clock state. This scheme improves coherence by many orders of magnitude, but stillsuffers from lattice light scattering because of the proximity of the resonance. We propose twopaths toward reaching ultralong trapping times. Firstly, we have identified a series of nearresonant magic wavelengths that should scatter minimally, and have begun preparing lasersystems to implement them. Secondly, we have discovered the possibility that vibrational statepairs in molecules are likely to have nonresonant magic wavelengths, which would extend thecoherent trapping times to multiple seconds, on par with those of atomic lattice clocks. Thesemagic traps, engineered near the telecom wavelengths, will be demonstrated in this work.Molecular clocks present many complementary and advantageous features to atomic clocks,including extremely long natural lifetimes of vibrational clock states and the availability ofdozens of suitable clock transitions within a single molecular species. This feature will allow usto obtain an ultrahigh-precision measurement of the van der Waals force between the atoms,challenging state-of-the-art quantum chemistry, and, combined with clock spectroscopy ofadditional molecular isotopologues, is expected to shed light onto the most fundamental nature ofthe interatomic bond. This same feature can greatly suppress systematic effects and facilitatetheir characterization, for example, helping cancel blackbody-radiation-induced shifts andleading to a novel and competitive platform for time and frequency metrology. In this work wewill make fundamental advances in molecular metrology and push the limits of van der Waalsforce measurements at the nanometer scale. Finally, we will extend ideas developed with thelattice-trapped strontium molecules, such as quantum-state-controlled photodissociation intoultralow-energy fragments, and apply them more broadly, in particular to produce physically andchemically interesting ultracold species that are not accessible via direct cooling. The proposedwork is based on a series of successful ONR funded projects in our laboratory, and is directly inline with many stated ONR interests in quantum control of molecules, metrology with trappedmolecules, and development of new techniques for ultracold physics and chemistry. The ONRgoals of improving timekeeping and sensing will be advanced by the state-of-the-art control ofmolecular quantum states.