A dual-species ¹⁷¹Yb⁺ / ⁸⁸Sr⁺ optical clock

Optical clocks based on spectroscopy of single ions have realized record fractional systematic uncertainties below the 10^-18 level. Recently, high-accuracy operation has also been extended to multi-ion clocks, which offer improved measurement stability. Here, we present a new multi-ion clock platform based on a linear chain of co-trapped ⁸⁸Sr⁺ and ¹⁷¹Yb⁺ ions. Dual-species operation promises a number of benefits. For example, we investigate how continuous laser cooling of ⁸⁸Sr⁺ can reduce heating of motional modes during clock interrogation of ¹⁷¹Yb⁺. Significant mitigation of ion heating opens the door to longer atomic coherence times, potentially set by the minutes-long background-gas-limited vacuum lifetime. Further, access to multiple clock transitions with differential sensitivities to external perturbations can enable improved systematic uncertainties. Finally, we discuss the possibility of implementing techniques from multi-ensemble metrology and quantum information for enhanced stability, as well as applications to fundamental physics, including new bounds on ultralight dark matter over multiple orders of magnitude in particle mass.