current work

Molecular Ion Quantum State Control

Even though sympathetic cooling slows down the velocity of our trapped molecular ions, unless we take extra care, they continue to rotate wildly with energies corresponding to room temperature. We have developed a simple pulse-shaped optical pumping technique to prepare "alkali-like" trapped molecules in their lowest quantum state. Using 2-photon dissociative state analysis, we demonstrate that the technique works very well to rotationally cool AlH+. Histograms are shown to the left, with the blue and green data points obtained for different pulse-shaping arrangments. We are currently gathering data to confirm that the cooling rate is as fast as expected. Manuscript published in Nature Communications. We are currently working toward hyperfine state preparation and creation of rotational wavepacket states.

Non-Destructive State Readout

Reading out the quantum state of a single or a few trapped molecular ions is often not so difficult, if we are willing to destroy the molecules in the process. If we want to keep them around for another experiment, e.g. when performing single-molecule spectroscopy, then we need some way to non-destructively read out the quantum state. Fluorescence readout of special "alkali-like" molecular ions and state readout by co-trapped atomic ions are two techniques we are currently developing. These techniques are also potentially important for quantum information processing applications.

Single-Molecule Spectroscopy and Time-Variation of Electron-Proton Mass Ratio

In the single molecular ion spectroscopy experiment, an AlH+ ion is co-trapped and sympathetically cooled by a single barium ion (Ba+) in a millimeter-scale linear Paul trap (photo to the left). The molecular ion is internally cooled by our pulse-shaped rotational cooling technique. To read out the spectroscopy result, we will apply a state-dependent optical driving force on the molecule that conditionally excites the two-ion secular motion, to be detected via Ba+ fluorescence. With the ability to perform non-destructive spectroscopy on a single trapped molecule, we can perform a high-precision search for time-variation of the electron-proton mass ratio, by comparing the AlH+ vibrational frequency to an optical frequency standard and watching for changes over the course of a year.