Quantum network test checks entanglement without having to trust detectors

Quantum networks connect devices using principles of quantum mechanics, with entanglement being a key feature. However, verifying entanglement in such networks typically requires trusting detection equipment. Researchers at Shandong University developed a new method for entanglement verification that doesn't require trust in measurement devices or extra photons for testing.

The team's approach, detailed in a paper in Physical Review Letters, uses two properties of photons - arrival times and optical polarization - to verify entanglement. By measuring these properties jointly on each photon, they can confirm entanglement without relying on trusted measurement devices. The method was tested successfully in a quantum network with four users, connecting them through six entangled links spanning 20 km of optical fiber each.

This method not only verifies entanglement but also quantifies it, providing a lower bound on the amount shared between users. It requires fewer experimental resources compared to previous methods since it uses the same photons for both entanglement and verification. The researchers believe this approach could make entanglement verification more practical for larger quantum networks, which have more connections and increased complexity.

Future work will explore extending this approach to larger networks and more complex entanglement scenarios.