reentangle

Reentangle is a term used in quantum information science to describe the process of creating entanglement between quantum subsystems that have become separable or that have never interacted, effectively restoring or establishing quantum correlations. Entanglement, a key resource for quantum computation and communication, can deteriorate due to noise, loss, or decoherence, and reentangling aims to recover functional entanglement for subsequent tasks.

Common routes to reentanglement include unitary interactions that couple the subsystems directly, measurements that herald entanglement, and heralded protocols such as entanglement swapping and purification. Entanglement swapping uses intermediate entangled pairs to entangle distant qubits that have not interacted, enabling a remote reentanglement of the end systems. Purification or distillation employs multiple imperfect entangled pairs and local operations with classical communication to produce fewer, higher-fidelity entangled pairs, effectively reestablishing usable entanglement.

In practical settings, reentanglement is central to quantum networks and repeaters, where entanglement must be reestablished across long distances despite losses and noise. It also supports distributed quantum computation and quantum sensing, where refreshed entanglement improves performance.

Challenges remain, including imperfect operations, limited success probabilities, and the overhead required for purification and swapping. Ongoing research seeks more efficient protocols, fault-tolerant implementations, and scalable architectures to reliably reentangle in noisy, real-world environments. See also entanglement, entanglement swapping, purification, distillation, and quantum repeater.