Assisted quantum teleportation

Teleportation through a non-maximally entangled pair, e.g., ket{ψ(θ)}_AB=cosθket{00}+sinθket{11}, induces a noisy channel and cannot achieve deterministic unit-fidelity transmission unless θ=π/4. We introduce a framework of assisted quantum teleportation in which a third party (the "Bank") supplies auxiliary multipartite entanglement to restore a perfect Bell pair on the original AB registers. We analyze two operational roles for the Bank: a Bank-measures model (measurement and broadcast) and a transfer model (the Bank transfers its subsystem and then leaves). For GHZ-class and W-class assistance we derive explicit feasibility regions for deterministic restoration and show an operational inequivalence for W resources. We further characterize finite-shot optimal success probabilities for probabilistic restoration and formulate Bank-measures feasibility for general pure Bank resources as a minimax optimization.