High-fidelity entanglement of 43Ca+ hyperfine clock states

In an experiment using the odd calcium isotope Ca-43(+), we combine the merits of a high-fidelity entangling operation on an optical transition (optical qubit) with the long coherence times of two clock states in the hyperfine ground state (hyperfine qubit) by mapping between these two qubits. For state initialization, state detection, global qubit rotations, and mapping operations, errors smaller than 1% are achieved, whereas the entangling gate adds errors of 2.3%. Based on these operations, we create Bell states with a fidelity of 96.9(3)% in the optical qubit and a fidelity of 96.7(3)% when mapped to the hyperfine states. In the latter case, the entanglement is preserved for 96(3) ms, exceeding the duration of a single gate operation by three orders of magnitude.