Building Blocks for Microwave Quantum Communication
Quantum communication relies on the ability to create and distribute quantum correlations, or entanglement. In one promising approach, entanglement is realized between continuous variables—such as the amplitude or phase of light. Over the past few decades, researchers have showcased key building blocks of continuous-variable quantum communication based on optical light. Now Baleegh Abdo and his colleagues at IBM Quantum in New York have extended those demonstrations to microwave radiation [1]. This work could help scientists attain long-distance quantum communication, secure quantum cryptography, and scalable quantum computing.
The researchers report three essential elements of continuous-variable microwave quantum communication. The first is a device that can efficiently entangle two microwave signals sent through separate transmission lines. This device is based on a superconducting circuit called a nondegenerate Josephson mixer. The second is an apparatus that uses two such devices to achieve quantum teleportation, whereby a quantum state—in this case, of a microwave signal—is transmitted without physically sending it. The third element is a system that uses three of the devices to realize entanglement swapping, a way to entangle quantum objects—here, microwave signals—that do not directly interact.
Abdo and his colleagues found that their teleportation apparatus could transmit the quantum state of a microwave signal with a maximum accuracy of 73%, exceeding the limit of 50% for sending the state without entanglement. They suggest that the maximum accuracy could be pushed to 95% if microwave losses in the apparatus were fully addressed. Both the entangling device and the entanglement-swapping system generated strong quantum correlations at a relatively high rate and could also be improved, the team says.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.
References
- B. Abdo et al., “Teleportation and entanglement swapping of continuous quantum variables of microwave radiation,” Phys. Rev. X 15, 031075 (2025).