Curator's Take
AI Commentary
This article demonstrates the first coherent optical link that can ferry microwave control pulses and phase references across a 10‑km fiber to operate superconducting qubits in separate dilution refrigerators, effectively providing a classical “backbone” for modular quantum processors. By achieving universal two‑qubit gates and an 80 % Bell‑state fidelity between a transmon and a cavity qubit located in different cryostats, the work bridges a gap between on‑chip control and long‑distance quantum networking that earlier experiments could only address within a single fridge. The result opens a realistic path toward scalable distributed architectures for computation, communication and sensing, although further improvements in transducer efficiency will be needed to push fidelities into fault‑tolerant regimes.
— Mark Eatherly
Summary
Distributed quantum networks are important for scalable quantum processors and for potential applications in communication, distributed computation, and sensing, in which direct classical links for adaptive control are essential to harness the shared entanglement. However, controlling superconducting quantum processors from a separate refrigerator over long distances remains elusive. Here, we introduce a coherent optical link (COL) that delivers microwave waveforms and their phase references between dilution refrigerators. Combining a laser, a microwave-to-optical transducer and an optical-to-microwave photodiode, the COL transmits microwave control signals over 10~km of fiber, while optical references derived from the same laser compensate for the frequency mismatch between devices. Through the COL, we deliver a universal gate set to a transmon qubit and a cavity qubit in another refrigerator and entangle them, and achieve a Bell-state fidelity of 80.6\%. Quantum control delivered through the COL thus provides a classical backbone for modular quantum processors.