Entanglement Across Separate Silicon Dies in a Modular Superconducting\n Qubit Device

Assembling future large-scale quantum computers out of smaller, specialized\nmodules promises to simplify a number of formidable science and engineering\nchallenges. One of the primary challenges in developing a modular architecture\nis in engineering high fidelity, low-latency quantum interconnects between\nmodules. Here we demonstrate a modular solid state architecture with\ndeterministic inter-module coupling between four physically separate,\ninterchangeable superconducting qubit integrated circuits, achieving two-qubit\ngate fidelities as high as 99.1$\\pm0.5$\\% and 98.3$\\pm$0.3\\% for iSWAP and CZ\nentangling gates, respectively. The quality of the inter-module entanglement is\nfurther confirmed by a demonstration of Bell-inequality violation for disjoint\npairs of entangled qubits across the four separate silicon dies. Having proven\nout the fundamental building blocks, this work provides the technological\nfoundations for a modular quantum processor: technology which will accelerate\nnear-term experimental efforts and open up new paths to the fault-tolerant era\nfor solid state qubit architectures.\n