Investigation of sympathetic cooling for an ion trap quantum computer with⁹Be⁺and ⁴⁰Ca⁺

One important source of finite infidelities in trapped-ion quantum logic gatesis due to the heating of motional modes [1]. One possibility to reduce this error source is the use of additional, ancillary ions to cool the logic ions prior to gate operations [2]. The logic ions can then be cooled indirectly via the Coloumb interaction while preserving the internal quantum states. We examine the choice of ⁹Be⁺ as logic ions along with ⁴⁰Ca⁺ as ancilla ion for the QVLS Q1 project. Due to the unfavorable mass ratio, the coupling of the normal modes is vanishingly small and therefore the interaction between the ions reduced. We study the expected cooling rates and discuss possibilities, such as parametric coupling [3], to achieve cooling times that are sufficient for quantum computing. Other choices of logic- and ancilla ions are discussed.

[1] D.J. Wineland et al., J. Res. Natl. Inst. Stand. Technol. 103, 259, 1998

[2] D. Kielpinski et al., Phys. Rev. A. 61, 032310, 2000

[3] P. Hou et al., arXiv:2205.14841 , 2022