Toward Scalable Quantum Networks: Lessons from InterQnet#

Rajkumar Kettimuthu (Argonne National Laboratory)

• Why: Not the PM's daily bread, but a two-year progress report on the US DOE's full-stack quantum networking program that frames quantum networks as an operations problem — and argues NRENs already own the prerequisites (deployed fiber, automation, synchronization, optical-channel engineering).
• What: InterQnet runs two tightly coupled goals. InterQnet-Achieve: a three-node heterogeneous quantum network (Yb atom arrays, Er³⁺ ions, superconducting qubits) over deployed campus fiber with dark-fiber paths toward Fermilab, UChicago, and StarLight, using frequency conversion and microwave-to-optical transduction, under centralized SDN-style orchestration with automated calibration. InterQnet-Scale: architecture studies via SeQUeNCe, Argonne's ~7-year-old quantum network simulator, with device-faithful simulations checked against real measurements. Hardware progress cited: 0.95 spin–photon fidelity with parallelized entanglement demonstrated on a 5-atom Yb array at 1389 nm; 1000× linewidth narrowing and telecom-band emission for Er; improved resonator yield for transducers.
• How: The co-design loop is the point — devices inform simulation, simulation guides architecture, architecture feeds back into hardware requirements — explicitly because the field's gap is between lab experiments and scalable architecture (no interoperable abstractions, no standard way to request entanglement, no common scalability metrics).
• Where applicable: Research program, not deployable today — but the framing that quantum networking resembles early classical networking (manual setup, static config, platform-specific interfaces) and that scale requires architecture, abstraction, and operations is exactly the signal to watch.