High-Fidelity Bell-State Preparation With Ca-40(+) Optical Qubits

Entanglement generation in trapped-ion systems has relied thus far on two distinct but related geometric phase gate techniques: Molmer-Sorensen and light-shift gates. We recently proposed a variant of the light-shift scheme where the qubit levels are separated by an optical frequency [B. C. Sawyer and K. R. Brown, Phys. Rev. A 103, 022427 (2021)]. Here we report an experimental demonstration of this entangling gate using a pair of C-40(+) ions in a cryogenic surface-electrode ion trap and a commercial, high-power, 532 nm Nd:YAG laser. Generating a Bell state in 35 mu s, we directly measure an infidelity of 6(3) x 10(-4) without subtraction of experimental errors. The 532 nm gate laser wavelength suppresses intrinsic photon scattering error to similar to 1 x 10(-5).