Robust entanglement detection and preservation in bilocal and networked quantum systems

Entanglement is central to quantum technologies, but its reliable detection and preservation remain challenging. Standard tools such as the Clauser-Horne-Shimony-Holt (CHSH) inequality detect only a subset of entangled states and often disturb the system. We present a variational entanglement witness (VEW) that optimizes detection probabilities and extends verification beyond CHSH violations. To complement this, we introduce a nonlocal measurement framework that evaluates VEW and CHSH operators while protecting entanglement from wave function collapse. We further apply this approach to bilocality scenarios, demonstrating how correlations from independent entanglement sources can be verified without destruction. Extending to small quantum networks, we show that VEW combined with nonlocal strategies enables scalable entanglement detection. Simulations on superconducting chips confirm post-measurement entanglement preservation. These results broaden entanglement verification from bipartite systems to networked architectures, supporting secure communication, distributed computing, and advanced quantum applications.