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

TL;DR

This paper demonstrates experimental methods for self-testing complex quantum states in network configurations involving multiple independent sources, advancing device-independent quantum state certification.

Contribution

It extends self-testing techniques to multi-source quantum networks, enabling device-independent fidelity bounds for states in scalable network configurations.

Findings

Successfully implemented self-testing in two-source quantum network configurations.

Provided device-independent lower bounds on state fidelity.

Showcased potential for scalable quantum network certification.

Abstract

Self-testing is a method of quantum state and measurement estimation that does not rely on assumptions about the inner working of the used devices. Its experimental realization has been limited to sources producing single quantum states so far. In this work, we experimentally implement two significant building blocks of a quantum network involving two independent sources, i.e. a parallel configuration in which two parties share two copies of a state, and a tripartite configuration where a central node shares two independent states with peripheral nodes. Then, by extending previous self-testing techniques we provide device-independent lower bounds on the fidelity between the generated states and an ideal state made by the tensor product of two maximally entangled two-qubit states. Given its scalability and versatility, this technique can find application in the certification of larger networks of different topologies, for quantum communication and cryptography tasks and randomness generation protocols.