Aaron Leu

We report the achievement of single-qubit gates with sub-part-per-million error rates, in a trapped-ion
43Ca+ hyperfine clock qubit. We explore the speed and fidelity trade-off for gate times 4.4 ≤ t_gate ≤ 35 μs, and benchmark a minimum error per Clifford gate of 1.5(4) × 10^−7. Calibration errors are suppressed to < 10^−8, leaving qubit decoherence (T2 ≈ 70 s), leakage, and measurement as the dominant error contributions. The ion is held above a microfabricated surface-electrode trap that incorporates a chip-integrated microwave resonator for electronic qubit control; the trap is operated at room temperature without magnetic shielding.

Microwave-driven logic is a promising alternative to laser control in scaling trapped-ion based quantum processors. We implement Mølmer-Sørensen two-qubit gates on 43⁢Ca+ hyperfine clock qubits in a cryogenic ( ≈25 K) surface trap, driven by near-field microwaves. We achieve gate durations of 154 µs [with 1.0(2)% error] and 331 µs [0.5(1)% error], which approaches the performance of typical laser-driven gates. In the 331 µs gate, we demonstrate a Walsh-modulated dynamical decoupling scheme which suppresses errors due to fluctuations in the qubit frequency as well as imperfections in the decoupling drive itself.

We use electronic microwave control methods to implement addressed single-qubit gates with high speed and fidelity, for 43Ca+ hyperfine “atomic clock” qubits in a cryogenic (100 K) surface trap. For a single qubit, we benchmark an error of 1.5×10^−6 per Clifford gate (implemented using 600 ns 𝜋/2
pulses). For 2 qubits in the same trap zone (ion separation 5  μ⁢m), we use a spatial microwave field gradient, combined with an efficient four-pulse scheme, to implement independent addressed gates. Parallel randomized benchmarking on both qubits yields an average error 3.4 ×10^−5 per addressed 𝜋/2
gate. The scheme scales theoretically to larger numbers of qubits in a single register.