Microwave-driven high-fidelity quantum logic with ⁴³Ca⁺

Magnetic field gradients produced in the near-field of a conductor carrying microwave current are sufficiently large to facilitate strong coupling between a trapped ion’s spin and motional degrees of freedom [1, 2]. Using this technique, we have previously shown that near-field microwave control of trapped-ion qubits is possible with two-qubit gate fidelities of 99.7(1) % [3], a fidelity which is approaching the state-of-the-art previously attained using laser-driven techniques.

Here we present the design and initial characterisation of a next-generation surface-electrode ion-trap designed for room-temperature or cryogenic operation, that will aim to improve both the fidelity and speed achieved in microwave-driven quantum gates. Improvements are targeted via a novel trap design and qubit choice. The trap is designed to produce large magnetic field gradients whilst passively partially-nulling the field amplitude. Further, operating at cryogenic temperatures leads to a reduction in ion heating rate and improved ion lifetime. The use of novel ⁴³Ca⁺ π-clock qubits operating at 288 G reduces the off-resonant excitation of ‘spectator’ transitions and facilitates an increase in gate speed.

References

[1] C. Ospelkaus et al., Phys. Rev. Lett. 101, 090502 (2008)

[2] C. Ospelkaus et al., Nat. 476, 181-184 (2011)

[3] T. P. Harty et al., Phys. Rev. Lett. 117, 140501 (2016)