High fidelity entanglement of 43Ca+ hyperfine clock states

TL;DR

This paper demonstrates high-fidelity entanglement of 43Ca+ hyperfine clock states, combining optical and hyperfine qubits to achieve long coherence times and robust quantum operations.

Contribution

It introduces a method to map between optical and hyperfine qubits in 43Ca+ ions, achieving high fidelity and long coherence times for entangled states.

Findings

Bell state fidelity of 96.9% in optical qubits

Bell state fidelity of 96.7% in hyperfine states

Entanglement preserved for 96 ms, much longer than a single gate duration

Abstract

In an experiment using the odd calcium isotope 43Ca+ 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.