Quantum-Logic Control and High-Resolution Spectroscopy of a Single Molecular Ion

Michael Drewsen

Fabian Wolf, Yong Wan, Jan C. Heip +3 more

Alejandra Collopy, David R. Leibrandt, Dietrich G. Leibfried +1 more

Quantum logic enables state preparation, readout and spectroscopy of otherwise difficult-to-study ions. Using the coupled harmonic motion shared between co-trapped ions, information can be transferred from the "spectroscopy" ion to the easily manipulated "logic" ion. With this technique we perform high-resolution terahertz-scale rotational spectroscopy of a single CaH+ molecular ion in pure states by leveraging a Ca+ ion as our logic ion. Entangled states between a CaH+ and a Ca+ have also been demonstrated, making molecular ions possible components of hybrid systems for quantum information processing. Because all our laser operations on the molecule are driving stimulated Raman transitions with high detuning, the technique promises to be generalizable to a wide variety of molecular ion species. Additionally, we study the systematic effects of the trap RF electric field on molecular levels and use it to obtain a measurement of the dipole moment of the charged molecule.

David Hanneke, Edward Kleiner, Alexander Frenett

David Holzapfel, Fabian Schmid, Nick Schwegler +5 more

Science is founded on the benchmarking of theoretical models against experimental measurements, with the challenge that, for all but the simplest systems, the calculations required for high precision become extremely challenging. H 2 + is the simplest stable molecule, and its structure is calculable to high precision. However, studying H 2 + experimentally presents significant challenges: Standard control methods such as laser cooling are not applicable due to the long lifetimes of its rotational and vibrational states. Here, we solve this issue by combining buffer gas cooling to quench the H 2 + rovibrational excitation with quantum logic operations between H 2 + and a cotrapped “helper” ion to control the molecule’s hyperfine structure. This enables us to perform pure quantum state preparation, coherent control, and nondestructive readout, which we use to demonstrate high-resolution microwave spectroscopy in the hyperfine structure of H 2 + with a precision of 2 Hz. Our results pave the way for high-precision spectroscopy of H 2 + in both the microwave and optical domains. Because of the wide applicability of buffer gas cooling, our method provides a general tool for molecular ion species that are hard to control with quantum logic tools alone.

C. W. Chou, Christoph Kurz, David B. Hume +3 more