Integrated optical implementation of multi-ion quantum logic*

Practical and useful quantum information processing will require improvements in operation fidelity and robustness, and simultaneously in scale and integration. Ion qubits’ fundamental qualities are promising for long-term systems, but the optics used to precisely control and measure their quantum states are a challenge to scaling. Previous work with single ions has suggested that trap-integrated optics may make this control more robust, and simultaneously parallelizable [1]. We have designed and implemented planar traps with integrated waveguides and grating couplers, for controlling multiple 40Ca+ ions. We measure 1.5 dB direct fiber-to-chip coupling losses, eliminating the need for beam alignment into vacuum systems/cryostats. Using these photonics, we have realized two-qubit entangling gates with fidelities over 97%, with understood errors suggesting significant possible improvement. The experimental realization of high-fidelity quantum logic in this platform suggests it can enable larger systems in multiple zones connected by transport [2].

[1] K.K. Mehta, et al. Nat. Nano., 11, 1066-1070 (2016).
[2] D. Kielpinski, et al. Nature 417, 709-711 (2003).