Experimental robust self-testing of the state generated by a quantum network

In this work, we deal with the verification that the state generated by a quantum network corresponds to the desired target, with no assumptions on the adopted experimental platform, i.e. device-independently. Such a task is known as self-testing and its experimental implementations have been limited so far, by the fact that the majority of the existing protocols have low noise tolerance. In our case, we develop self-testing methods to deal with real imperfect conditions and show their applications to two experimentally implemented quantum networks.
In detail, our target is the tensor product of two maximally entangled two-qubit states and we provide lower bounds on the fidelity between the generated states and such an ideal state, extending previous self-testing techniques.
On the experimental side, we implement two quantum network building blocks, involving two independent sources, on a photonic platform. Firstly, a parallel configuration in which two parties share two quantum states and a tripartite configuration where a central party shares two states with peripheral nodes. Given their versatility, the techniques we show can be applied to the certification of larger networks of different topologies, for quantum communication, cryptography and randomness generation protocols.