Karan Mehta, ETH Zurich
Practical and useful quantum information processing will require significant jumps with respect to current systems in error rates and robustness of basic operations, and at the same time in scale and integration. Individual ion qubits’ fundamental qualities are compelling for long-term systems, but a significant challenge in scaling to large ion numbers lies in the optics used to precisely initialize, manipulate and measure their quantum states. Planar-fabricated optics integrated within surface-electrode traps may make these processes more robust, and simultaneously parallelizable . I will discuss an approach to systems capable of handling well beyond tens of trapped-ion qubits, and recent experimental work utilizing silicon-nitride waveguides and gratings integrated within planar traps for controlling multiple 40Ca+ ions . These devices exhibit measured direct fiber-to-chip coupling losses of 1.5 dB on multiple channels at the relevant visible wavelengths, eliminating the need for beam alignment into vacuum systems/cryostats. We have used such devices to enable high-fidelity and powerefficient two-qubit entangling gates in a cryogenic environment; these recent results suggest such approaches may assist in computationally nontrivial experiments. I will give an outlook towards more general operations on larger systems, and at fast (~μs) timescales.
 K.K. Mehta, C.D. Bruzewicz, R. McConnell, R.J. Ram, J.M. Sage, and J. Chiaverini. “Integrated optical
addressing of an ion qubit.” Nature Nanotechnology 11, 1066-1070 (2016).
 K.K. Mehta, C. Zhang. S. Miller, J.P. Home. “Towards fast and scalable trapped-ion quantum logic with integrated
photonics.” Proc. SPIE 10933 (2019).