Robust self-testing with applications to device-independent cryptography
The quantum revolution is happening now. Every day experimentalists around the world produce more complex, reliable and powerful quantum devices which take us one step closer to quantum computation, communication and cryptography. Testing is a crucial part of the development process necessary to ensure suitability of the device for the application in mind. Methods used for small devices quickly become impractical, as the devices become more complex and we need to develop efficient and robust testing procedures in order to make further progress. Fortunately, quantum physics is well-suited for this task, as it allows to precisely characterise devices under surprisingly weak assumptions. This feature, known as self-testing, is intrinsically related to the fundamental concept of Bell inequalities. The goal of this proposal is to develop efficient and robust testing procedures for complex quantum devices based on Bell's theorem. In the short-term these will allow experimentalists to efficiently characterise their devices, while in the long-term they will enable a customer to certify that a newly bought quantum device adheres to the specification, which opens the door to device-independent information processing. The timeliness of this proposal is demonstrated by the fact that the first loophole-free Bell experiments were reported within the last year. On top of practical applications, self-testing is important from the foundational point of view. By exploring the intimate connection between the quantum (microscopic) world of Hilbert spaces and the classical (macroscopic) world of resulting probability distributions, it provides the unique link between what we see and what is happening at the quantum level. This fellowship will allow Jędrzej Kaniewski to work under the supervision of Matthias Christandl (a world-class expert on quantum correlations) at the University of Copenhagen (a leading institution in both theoretical and experimental aspects of quantum mechanics).