Long-range quantum entanglement using molecular ions

Y.-C. Lin, Y. K. Ho

Markus Deiß, Shinsuke Haze, Johannes Hecker Denschlag

We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom due to the electric field of the ion. At particular internuclear distances between the Rydberg atom and the ion, potential wells occur that can hold atom–ion molecular bound states. Apart from the binding mechanism, we describe important properties of the long-range atom–ion Rydberg molecule, such as its lifetime and decay paths, its vibrational and rotational structure, and its large dipole moment. Furthermore, we discuss methods of how to produce and detect it. The unusual properties of the long-range atom–ion Rydberg molecule give rise to interesting prospects for studies of wave packet dynamics in engineered potential energy landscapes.

Aaron T. Calvin, Kenneth R. Brown

In this Perspective, we examine the use of laser-cooled atomic ions and sympathetically cooled molecular ions in Coulomb crystals for molecular spectroscopy. Coulomb crystals are well-isolated environments that provide localization and long storage times for sensitive measurements of weak signals and cold temperatures for precise spectroscopy. Coulomb crystals of molecular and atomic ions enable the detection of single-photon molecular ion transitions at a range of wavelengths by a change in atomic ion fluorescence at visible wavelengths. We give an overview of the state of the art from action spectroscopy to quantum logic spectroscopy for a wide range of molecular transitions from rotational sublevels separated by 10 –7 cm –1 to rovibronic transitions at 25 000 cm –1 . We emphasize how this system allows for unparalleled control of the molecular ion state for precision spectroscopy with applications in astrochemistry and fundamental physics. We conclude with an outlook of the use of this control in cold molecular ion reactions.

David L. Moehring

Tobias Schaetz

A Mortensen, E Nielsen, Thierry Matthey +1 more

We report on the observations of strikingly persistent (lifetimes of ∼10 s) three-dimensional long-range ordered structures in the central 40 Ca + ion component of 40 Ca + – 44 Ca + two-species ion Coulomb crystals in a linear Paul trap. Molecular dynamics simulations strongly indicate that the observed structures are a hitherto unpredicted consequence of an effective anisotropy in the inter-particle interaction induced by the radio frequency quadrupole-trapping field. The results have implications for such diverse research fields as cold molecular ion studies and quantum information processing.