A new three-dimensional (3D) integrated quantum processor featuring vertically stacked qubit chips connected via a novel multilayer flip-chip bonding technique has been created by Xudong Liao and colleagues at Nanjing University, in collaboration with Tencent Quantum Laboratory. The architecture uses both planar and vertical tunable couplers to achieve high-fidelity qubit control, demonstrating single-qubit gate fidelities of 99.87% and controlled-Z gate fidelities of 97.5% for both within-chip and between-chip operations. Successful demonstration of high-fidelity Bell-state preparation and a four-qubit W state confirms the potential of vertical coupling as a viable route towards building scalable quantum computers capable of implementing advanced quantum error correction.
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