High-Fidelity Bell-State Preparation with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:msup><mml:mrow><mml:mi>Ca</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>40</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> Optical Qubits
Craig R. Clark, Holly N. Tinkey, Brian C. Sawyer, Adam M. Meier, Jan‐Karl Burkhardt, Christopher M. Seck, Christopher M. Shappert, Nicholas D. Guise, Curtis Volin, Spencer D. Fallek, Harley Hayden, Wade G. Rellergert, Kenton R. Brown
Abstract
Entanglement generation in trapped-ion systems has relied thus far on two distinct but related geometric phase gate techniques: M\o{}lmer-S\o{}rensen 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 ${^{40}\mathrm{Ca}}^{+}$ ions in a cryogenic surface-electrode ion trap and a commercial, high-power, 532 nm Nd:YAG laser. Generating a Bell state in $35\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, we directly measure an infidelity of $6(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ without subtraction of experimental errors. The 532 nm gate laser wavelength suppresses intrinsic photon scattering error to $\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.