Abstract
Trapped Rydberg ions are a promising new system for quantum information processing. They have the potential to join the precise quantum operations of trapped ions and the strong, long-range interactions between Rydberg atoms. Technically, the ion trap will need to stay active while exciting the ions into the Rydberg state, else the strong Coulomb repulsion will quickly push the ions apart. Thus, a thorough understanding of the trap effects on Rydberg ions is essential for future applications. Here we report the observation of two fundamental trap effects. First, we investigate the interaction of the Rydberg electron with the quadrupolar electric trapping field. This effect leads to Floquet sidebands in the spectroscopy of Rydberg D-states whereas Rydberg S-states are unaffected due to their symmetry. Second, we report on the modified trapping potential in the Rydberg state compared to the ground state which results from the strong polarizability of the Rydberg ion. We observe the resultant energy shifts as a line broadening which can be suppressed by cooling the ion to the motional ground state in the directions orthogonal to the excitation laser.
Highlights
Trapped ions are one of the most mature implementations of a quantum computer
Note that the Rydberg ions do not get doubly ionized by the trapping electric fields, as ions are generally held at the null of the electric quadrupole fields, at least given that stray electric fields leading to micromotion of the ion are properly compensated
We investigate several elementary trap effects of Rydberg ions, which will be essential for future applications in quantum technologies
Summary
Trapped ions are one of the most mature implementations of a quantum computer. The trapped ion approach has set several benchmarks with qubit lifetimes up to minutes [1], entanglement operations with error probabilities smaller than 10−3 [2,3], and with up to 14 entangled qubits [4]. A similar entanglement method has been demonstrated with neutral atoms [23,24,25] In this sense trapped Rydberg ions promise to join the advantages of both technologies: they combine the strong dipolar interaction between Rydberg atoms with the precise quantum control and long storage times of trapped ions. Combining these systems is by no means trivial. A further novel property of Rydberg-excited ions is that their trapping potential is modified compared to their ground state, which can, e.g., induce structural phase transitions in an ion crystal [28] This effect is caused by the strong polarizability of the Rydberg state, which becomes polarized in the trapping electric fields. We see the modified trapping potential as a line broadening for a Doppler-cooled ion with a thermal population distribution, as compared to a sideband-cooled ion where most of the population resides in the motional ground state
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