15 February 2011 ICFO in Nature Comm.

Researchers at National University of Singapore and
the group led by Prof. Antonio Acin present new results in quantum non-locality.
Nature Communications features in its last issue the paper ‘Quantum networks reveal quantum non-locality`, by Dr. Daniel Cavalcanti, National University of Singapore; Prof. Valerio Scarani, CQT (Center for Quantum Technologies, National University of Singapore); former ICFOnian Dr. Mafalda Almeida and ICFO group leader and ICREA Prof. Antonio Acín.

The authors create a new scenario for the study of non-locality in quantum networks and show that non-locality of quantum states strongly depends on the measurement context.

Figure (a) shows the simplest case for the standard scenario for the study of quantum non-locality. It consists of n (in this case two) parties sharing one copy of an n-party quantum state. In the new scenario, many copies of the quantum state are distributed among N>n parties according to a network configuration, as shown in figure (b).

If the resulting network state displays non-local correlations, the initial quantum state has to be non-local. The authors prove that this new scenario is stronger than the standard, as there are quantum states that are local according to (a), but provide nonlocal correlations when distributed in a network as in (b). These results provide new grounds to understand and implement the quantum phenomenon of non-locality.