Quantum Entanglement Self-testing Protocol.  Quantum entanglement is key to quantum information processing.  With the fragile state of quantum bits, device-independent certification of entangled states demands self-testing.  “The central aim of self-testing is to certify the state and measurements of quantum systems without any knowledge of their inner workings, even when the used devices cannot be trusted.”  Scientists at the University of Science and Technology of China, have developed a self-testing method “as a practical tool for developing quantum techniques.”  In their work, the team implements a proof-of-concept experiment for a complete entangled state self-testing protocol.  Such a protocol, when properly established, may permit enhanced fidelity in results of quantum information.

 

“Experimental setup to self-test pure unknown bipartite systems. The setup includes an entanglement source and a measurement apparatus for self-testing. In brief, entangled photon pairs are generated by pumping a periodically poled KTP (PPKTP) crystal in a polarization Sagnac interferometer (SI), and then they are encoded into polarization and path modes to produce high-dimensional entanglement. A hybrid measurement apparatus can perform arbitrary projective measurements on polarization and path modes. BD beam displacer, HWP half wave plate, QWP quarter wave plate, DM dichroic mirror, BPF bandpass filter, PBS polarized beam splitter, SMF single mode fiber.” (Image Credit: https://www.nature.com/articles/s41534-018-0120-0/figures/2)

Reference is found at nature.com…