Opening the black box: how to estimate physical properties from non-local correlations

23 10/2013

Wednesday, 23 Oct. 2013, 14:00 - 15:00

Workgroup Brukner Group

Presenter: Miguel Navascues, School of Physics, University of Bristol
Host: C. Brukner
Where: IQOQI Seminar Room, 2nd Floor, Boltzmanngasse 3, 1090 Vienna

In the device-independent approach to quantum information theory, quantum systems are regarded as black boxes which, given an input (the measurement setting), return an output (the measurement result). In this talk, I will introduce SWAP, a theoretical tool which, in combination with known numerical methods for the characterization of quantum correlations, allows us to estimate general properties of the underlying state and quantum measurements from the observed measurement statistics. As an illustration of the power of the new approach, I provide robust bounds on the state fidelity for the CHSH scenario: a CHSH violation larger than 2.57 gives a fidelity of more than 70% between the black box quantum state and the singlet. Also, I show that the maximal violation of the CGLMP inequalities can only be achieved with non maximally entangled states, and robustly self test quantum states in the CGLMP scenario, for which Jordan's Lemma cannot be used. The SWAP method can also be extended to estimate in a robust manner the amount of extractable work in CHSH-violating systems, providing a link between thermodynamics and nonlocality. Lastly I show how to use SWAP to certify entangling measurements in tripartite non-locality scenarios.

Joint work with T. H. Yang, T. Vértesi, J.-D. Bancal and V. Scarani, arXiv:1307.7053.