Toward quantum-logic spectroscopy of single molecular ions in a cryogenic ion trap*

Quantum state control of trapped and cooled atomic ions is an established technique with applications including precision metrology and quantum information processing. Molecules provide even richer physics, but their additional degrees of freedom make such control more challenging. In our group, quantum-logic spectroscopy (QLS) of a single CaH⁺ ion has enabled preparation and coherent manipulation of pure molecular quantum states [1, 2, 3]. However, the currently used loading scheme is applicable only to certain compounds of the co-trapped atomic species, and background gas collisions and black-body radiation in the room-temperature apparatus eventually limit measurement precision and fidelity of quantum control. Here, we present progress of the design and construction of a cryogenic ion trap apparatus for more versatile loading of molecular ions and better control of their states. Molecules will be injected from an interchangeable gas source, ionized in a strong laser field, and co-trapped with an atomic ion for QLS. Currently, construction of a vacuum chamber to allow for preliminary trapping and ionization tests is underway. This device will ultimately be used to perform precision spectroscopy of molecules relevant for, e.g., tests of fundamental physics.

[1] C.-W. Chou et al., Nature 545, 203 (2017).

[2] C.-W. Chou et al., Science 367, 1458 (2020).

[3] Y. Lin et al., Nature 581, 273 (2020).