Sympathetic Cooling Scheme in Same-Isotope Trapped-Ion Chains

An important requirement for realizing high-fidelity logical gates in trapped ions is for the collective motion of the ions to be near-ground state. This is typically achieved by sympathetically cooling a subset of ions between gate sequences, which results in cooling of the chain while preserving the qubit states of the data ions. Typical approaches for differentiating the coolant ions from the data ions include using a second species or mixed-isotope chains, but lead to challenges such as increased experimental complexity, re-ordering events and mass-mismatches, leading to reduced cooling efficiency of radial modes. We propose, demonstrate and characterize a sympathetic cooling scheme using identical atomic ions based on the omg-architecture, which utilizes Zeeman levels in the ion and individually addressed Raman transitions to achieve spectral isolation between the coolant ions and data ions. We demonstrate cooling of all radial modes in a five-ion chain, and show evidence of minimal impact on qubit coherence while the motional modes are cooled to near-ground state.