Abstract
Cooling the motion of trapped ions to near the quantum ground state is crucial for many applications in quantum information processing and quantum metrology. However, certain motional modes of trapped-ion crystals can be difficult to cool due to weak or zero interaction between the modes and the cooling radiation, typically laser beams. We overcome this challenge by coupling a mode that interacts weakly with cooling radiation to one that interacts strongly with cooling radiation using parametric modulation of the trapping potential, thereby enabling indirect cooling of the weakly interacting mode. In this way, we demonstrate near-ground-state cooling of motional modes with weak or zero cooling radiation interaction in multi-ion crystals of the same and mixed ion species, specifically , , and crystals. This approach can be generally applied to any Coulomb crystal where certain motional modes cannot be directly cooled efficiently, including crystals containing molecular ions, highly charged ions, charged fundamental particles, or charged macroscopic objects.
- Received 10 August 2023
- Accepted 4 March 2024
DOI:https://doi.org/10.1103/PhysRevX.14.021003
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Cooling of trapped ions or charged particles close to the zero-point energy of motion allows exploration of quantum information science and fundamental physics. However, certain motional modes in trapped-ion crystals are difficult to cool due to their weak interaction with cooling radiation, typically laser beams, hampering progress in various applications. Here, we introduce a method to efficiently cool these challenging modes indirectly.
Our method involves transferring motional quanta from weakly cooled modes to strongly cooled modes, thus allowing indirect cooling of the former. The essential technique is fast population exchange between two involved modes realized by parametric modulation of the trapping potential that confines the ions. Remarkably, we demonstrate that even modes with nearly or exactly zero direct cooling rates can attain final motional occupations close to those for direct, strongly cooled modes using this indirect cooling technique.
This method can be applied to any Coulomb crystal containing both coolant ions and other charged species of interest. It enables efficient sympathetic cooling in trapped-ion quantum computing, a scenario where data qubits holding quantum information cannot be directly laser cooled. It also supports a wide range of charge-to-mass ratios in crystals with mixed species of ions, expanding possibilities for using various atomic, molecular, and mesoscopic species in quantum metrology and fundamental physics experiments.
