Coherent Control and Precision Spectroscopy of a Polyatomic Molecular Ion

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This project is motivated by the opportunity to achieve coherent control of the quantum state of a single polyatomic molecule, and to exploit this control for precision measurements. This project will focus on trapping and controlling the molecular ion N_2H+, but the approach can be generalized to many other molecular ions. The N_2H+ molecular ion will be co-trapped and sympathetically cooled with a calcium ion to near the ground state of their shared motion. Pure quantum states of the molecular ion can then be initialized by projective measurements using quantum-logic spectroscopy, as recently demonstrated on the calcium hydride ion CaH+ by the investigators. This is important because this approach can advance quantum chemistry and may impact materials science and the chemical, biological, and pharmaceutical industries. In addition, new and superior reference spectra for astronomical observations could lead to a better understanding of interstellar gas clouds and the universe, including stringent tests of physics beyond the standard model. Ultimately, controlling molecules at the quantum level may enable precisely orchestrated collisions and fully controlled quantum chemistry.While laser cooling, trapping, and precision measurements of diatomic molecules are making tremendous progress, polyatomic molecules have eluded precision studies due to their complicated level structures and vast number of populated states. This project will extend the technique of quantum-logic spectroscopy to prepare pure quantum states of polyatomic molecules, and to manipulate and detect their states with minimal perturbations such as Doppler or pressure shifts. Precision spectroscopy will ultimately only be limited by the lifetime of the states and can therefore be pushed to levels that have only been reached previously in optical atomic clocks. The molecule N_2H+ was one of the first ions observed in interstellar clouds and remains one of the most important tracers in astrophysics. Improved spectroscopic precision might enable improved constraints on possible spatial or temporal variations of fundamental constants. This work will also train a student at the University of Colorado in techniques needed for quantum logic spectroscopy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.