Large-scale quantum networks require new technologies for coherently routing quantum information between distant quantum memories or processing nodes. Notably, low-noise transducers for coherent microwave-optical signals endeavor to combine two of the most successful quantum platforms together, allowing quantum photonic networks to establish entanglement links between distant superconducting qubit processors. Remarkable progress towards such components has been achieved in recent years [1], led in large part by the Loncar group at Harvard. Motivated by multiple successful demonstrations of low dissipation, nonlinear microwave-optical effects, such as high-speed modulation [2], second harmonic generation [3,4], and frequency conversion [4], we propose a new joint collaboration between Rigetti and the Loncar group to evaluate a systems-implementation of optically-linked superconducting qubit processors. In Phase I, we will develop the techniques to co-design both photonic and microwave quantum integrated circuits, as well as the accompanying coherent control protocols, in order to engineer robust chip-to-chip entanglement carried by optical photons. The key deliverables from Phase I will be 1) an optimized architecture for photon-superconductor networking and 2) the expected component-level requirements for a system to be built and tested during Phase II and beyond. The Department of Defenses ability to protect Americans hinges on its capacity to keep strategic and military plans confidential. More mature quantum network technology will provide complete end-to-end security and advance Air Force resilient information sharing by land, air, and space. Additional military and commercial-scale applications include, but are not limited to: access to quantum computers in the cloud, clock synchronization, enhancing and synthesizing observations from telescopes, achieving agreement on distributed data, quantum internet protocols, and a global quantum internet which ultimately leverages the power of quantum computers to operate on data transmitted in quantum states. Ultimately, building widespread quantum networks is central to the future of resilient information sharing, global persistent awareness, and rapid, effective decision-making.
