This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Quantum networks are systems that connect different users or devices using principles of quantum mechanics. In the future, these networks could help improve the security of communications.
For entanglement-based quantum networks to work, however, researchers need to be able to verify that particles are entangled and assess the extent of their entanglement. Entanglement is a quantum mechanical effect in which the shared states of distant particles cannot be described as separate or independent. Researchers at Shandong University recently introduced a new approach for verifying entanglement in a quantum network that does not require trusting the equipment used to analyze and detect photons (i.e., light particles), as most previously developed strategies do.
Their proposed method, outlined in a paper published in Physical Review Letters, was successfully used to verify entanglement in a quantum network with four users. "Building a quantum network is only part of the challenge," He Lu, senior author of the paper, told Phys.org. "We also need to know whether the entanglement distributed across the network is genuinely there.
My interest in this problem dates back to 2014, when I participated in one of the first experimental demonstrations of measurement-device-independent (MDI) entanglement witnessing." In their earlier work, Lu and his colleagues demonstrated that conventional entanglement verification techniques could be misled by measurements that were tampered with. Specifically, manipulating measurement results could trick conventional tests into detecting entanglement when none was present. They also tested an approach dubbed MDI entanglement witnessing that overcame this limitation.
Despite its potential, this approach required the preparation of additional photons in known states for testing, which complicated its implementation. "In recent years, our group has been developing broadband entangled-photon sources based on integrated lithium-niobate photonics," said Lu. "Meanwhile, fully connected quantum networks have been advancing rapidly, allowing entanglement to be distributed among multiple users.
These developments motivated us to revisit MDI entanglement verification in the context of quantum networks and explore whether it could be implemented more efficiently." The main goal of the team's recent study was to develop a new practical approach for reliably verifying and quantifying entanglement across a multiuser quantum network. Most importantly, they wanted this approach to work even without trusting measurement devices or preparing additional photons for testing. "We built our quantum network using a small photonic chip that generates pairs of entangled photons over a broad range of wavelengths," said Lu.
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