Abstract
Self-testing is a method of quantum state and measurement estimation that does not rely on assumptions about the inner working of the devices used. 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: namely, 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 target 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.Received 21 October 2020Revised 25 March 2021Accepted 3 May 2021DOI:https://doi.org/10.1103/PRXQuantum.2.020346Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum information processingQuantum networksQuantum nonlocalityQuantum Information
Highlights
In the last few years, a large number of quantum resource-based protocols have been designed, with a wide range of applications
We study a parallel self-testing scenario, in which two parties share two copies of a bipartite state, and a tripartite one, in which two bipartite states are shared among two peripheral nodes and a central one [50,51,52,53,54,55]
We are able to obtain lower bounds on the fidelity of the generated states with the desired target states that demonstrate that both sources produce entangled states, constituted by the tensor product of two two-qubit maximally entangled states
Summary
In the last few years, a large number of quantum resource-based protocols have been designed, with a wide range of applications It is crucial, and far from trivial, to discriminate the devices that work correctly from those that do not. Two difficulties can emerge: on one hand, the task required by the user may be hard to verify, a notorious example being the boson sampling problem [1,2,3,4,5], and, on the other, the devices may be affected by noise and imperfections that are unknown to the user The latter case is especially relevant for tasks aimed at being secure against possible adversaries, who could exploit such defects to obtain secret information or sabotage the operation of the devices. The ability to certify that the device is operating properly, and possibly without relying on knowledge of its internal working, is crucial for a wider application of quantum
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