Quantum communication requires networks of quantum processors connected through low-loss, low-noise channels to share entangled states. Superconducting microwave qubits, operating in cryogenic environments, are promising as processor nodes but face scaling issues due to their bulky components and high thermal loads.
Optical signals at telecommunication frequencies offer a smaller, more efficient alternative, avoiding problems like signal loss, noise sensitivity, and overheating. Linking optical and microwave frequencies is key to combining the benefits of optics with superconducting qubits, enabling efficient, low-loss connections.
Physicists at Harvard SEAS have developed a photon router that connects quantum networks to noise-sensitive microwave quantum computers. This microwave-optical quantum transducer enables control of superconducting microwave qubits—the basic quantum processing units—using optical signals from miles away.
With 1.18% conversion efficiency and low noise, it’s the first device to control superconducting qubits solely with light.
A key challenge in deploying superconducting microwave qubit platforms is their reliance on extremely low temperatures, requiring large dilution refrigerators.
As future quantum computers scale up to millions of qubits, using only microwave signals becomes inefficient. The solution combines microwave qubits for quantum operations with optical photons as scalable interfaces.
This is where the transducer comes in. The Harvard team has developed a compact optical device, just 2 millimeters in size, resembling a paper clip, mounted on a chip about 2 centimeters long.
It connects a microwave resonator with two optical resonators, enabling energy exchange thanks to lithium niobate’s properties. This design eliminates the need for bulky, heat-generating microwave cables to control qubit states.
The researchers emphasized that the breakthrough brings us closer to a world with superconducting quantum processors connected by low-loss, high-powered optical networks. The next step involves reliable generation and distribution of entanglement between microwave qubits using light.
Journal Reference
- Warner, H. K., Holzgrafe, J., Yankelevich, B., Barton, D., Poletto, S., Xin, C. J., Sinclair, N., Zhu, D., Sete, E., Langley, B., Batson, E., Colangelo, M., Joe, G., Berggren, K. K., Jiang, L., Reagor, M. J., & Lončar, M. (2025). Coherent control of a superconducting qubit using light. Nature Physics, 1-8. DOI: 10.1038/s41567-025-02812-0
Source: Tech Explorist
