Weak values and continuous-variable entanglement concentration

We demonstrate a general weak-measurement model which allows Gaussian-preserving entanglement concentration of the two-mode squeezed vacuum. The power of this simple and elegant protocol is through the constraints it places on possible ancilla states and measurement strategies that will allow entanglement concentration. In particular, it is shown how previously discovered protocols of this kind emerge as special examples of the general model described here. Finally, as evidence of its utility, we use it to provide another example of such a protocol.