In the theoretical study, recently published in Physical Review Letters and reviewed as research highlight, the researchers are asking the following fundamental question: is it possible to self-test a theory, and, in particular, quantum theory? Self-testing is usually referred to as a protocol to certify the specific quantum properties of a system under a small set of assumptions. For instance, in certain cases, the correlations observed when measuring a quantum system allows one to infer what state the system was in before the measurement. This certifies its quantum properties without the need to know any details of the measurement procedure or the system at hand.
In their recent publication, Mirjam Weilenmann and Roger Colbeck propose to extend the concept of self-testing of quantum systems to the theory itself. Quantum theory, in fact, is not the only possible theory to explain the physical world. It has been so far put through many tests to disprove it and has passed them all, but so far no method has been found able to single it out as the only correct theory.
The researchers now propose to achieve this by finding a set of correlations that cannot be explained in theories other than quantum mechanics. By measuring such correlations, it would be possible to establish quantum mechanics as the only possible theory amongst a range of alternatives. This could also constitute an insight into the physical principles underlying quantum theory. In fact, unlike other theories that have firm physical principles behind them, quantum mechanics is usually presented as a series of mathematical axioms whose underlying physical significance is unclear. The self-testing proposed by the researchers might help to bring new insights to answer the question of why quantum mechanics works. This could also have an impact on the search for future theories, such as candidates for unifying quantum mechanics and gravity.