Fig. 1: Experimental setup.

a Energy levels of ¹⁷¹Yb⁺ and ¹³⁸Ba⁺ ion and cutaway view of the μ-metal shielding enclosing octagon chamber. The shielding has ten holes, where two holes for connection of the vacuum pump and helical resonator and the other eight holes with diameter from 20 to 40 mm for the access of laser beams, microwave, and imaging system. b The schematic diagram for the control of microwave and laser beams. We use a crystal oscillator (SIMAKE SMK3627OCHFM OCXO) to reference the microwave generator and Direct Digital Synthesize (DDS) through a 1 GHz signal generator. The microwave of 12.6 GHz is generated by mixing 200 MHz signal from DDS and 12.4 GHz from the microwave generator, which is amplified and applied to ions through a horn. All three microwave switches are used to reduce microwave leakage. For 369 nm laser beams, we use acousto-optic modulators (AOMs) to generate basic operating lasers. We use Electro-Optic pulse picker (EOPP), mechanical shutter and single-mode fiber to reduce laser leakage. The magnetic-field direction is in the radial direction. We detect the qubit state with a photomultiplier tube (PMT).