Scaling up trapped-ion quantum information processors inevitably means that above some size scale, qubits will need to be distributed across multiple processing zones. Harnessing the full power of such an architecture for quantum information processing requires a method to couple qubits in separate zones. The “quantum charge-coupled device” architecture connects distant qubits by physically moving them together, but at the same time imposes overhead from time spent on shuttling ions. An alternative solution is to employ a teleported two-qubit entangling gate that uses only local operations within each zone, classical communication between zones, and a shared entangled qubit pair as a resource. This approach has been demonstrated probabilistically in photonic systems with post-selection and only recently performed deterministically between two superconducting cavity qubits by means of an entangled pair of transmons. Here we demonstrate a deterministic teleported CNOT gate between two beryllium ion qubits in spatially separated zones of a segmented Paul trap, using an entangled pair of magnesium ion qubits as the resource. A full process tomography is performed on the two beryllium ion, and a 95% confidence interval [0.845, 0.872] for the entanglement fidelity is inferred using maximum likelihood (ML) estimation. To detect departure from the model and to discover unchecked fluctuations, we applied a likelihood-ratio test to the tomography data, indicating inconsistency of our data with a single quantum process. We verify through numerical simulation and diagnosis on the experimental setup that slow drifts in the setup is the cause of this inconsistency, suggesting the importance of such consistency checks in addition to other benchmarking techniques.

This protocol combines ion shuttling with individually-addressed single qubit rotations and detection, high fidelity same- and mixed-species two qubit gates, and real-time conditional operations, thereby demonstrating the combination of essential tools for scaling trapped-ion quantum computers in a single device.

Bio:

Yong Wan graduated in 2010 from University of Stuttgart as a diplom physicist and pursued his doctoral study on precision spectroscopy on trapped ions at the University of Hannover and Physikalisch-Technische Bundesanstalt till 2014. Since then, he moved to National Institute of Standards and Technology and continued his research on trapped ions with the focus on trapped-ion quantum computing. His research interests include precision measurements, molecular ions, and trapped-ion quantum.