Preparation and coherent manipulation of pure quantum states of a single molecular ion

TL;DR

This paper demonstrates a method using quantum-logic spectroscopy to prepare and detect pure quantum states in molecular ions, enabling high-precision spectroscopy and quantum control with broad applicability.

Contribution

It introduces a general optical pumping technique for molecular ions, allowing their quantum states to be prepared and measured nondestructively in a versatile and scalable manner.

Findings

Successful preparation of pure quantum states in CaH+

Observation of Rabi flopping and Ramsey fringes in molecular ions

Method applicable to various molecular species with a single laser

Abstract

Laser cooling and trapping of atoms and atomic ions has led to numerous advances including the observation of exotic phases of matter, development of exquisite sensors and state-of-the-art atomic clocks. The same level of control in molecules could also lead to profound developments such as controlled chemical reactions and sensitive probes of fundamental theories, but the vibrational and rotational degrees of freedom in molecules pose a formidable challenge for controlling their quantum mechanical states. Here, we use quantum-logic spectroscopy (QLS) for preparation and nondestructive detection of quantum mechanical states in molecular ions. We develop a general technique to enable optical pumping and preparation of the molecule into a pure initial state. This allows for the observation of high-resolution spectra in a single ion (here CaH+) and coherent phenomena such as Rabi flopping and Ramsey fringes. The protocol requires a single, far-off resonant laser, which is not specific to the molecule, so that many other molecular ions, including polyatomic species, could be treated with the same methods in the same apparatus by changing the molecular source. Combined with long interrogation times afforded by ion traps, a broad range of molecular ions could be studied with unprecedented control and precision, representing a critical step towards proposed applications, such as precision molecular spectroscopy, stringent tests of fundamental physics, quantum computing, and precision control of molecular dynamics.