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).