Session M2: Invited Session: 50 Years of Bell's Inequalities

Bell nonlocality: a resource for device-independent quantum information protocols

Bell nonlocality is not only one of the most fundamental properties of quantum physics, but has also recently acquired the status of an information resource for device-independent quantum information protocols. In the device-independent approach, protocols are designed so that their performance is independent of the internal working of the devices used in the implementation. We discuss all these ideas and argue that device-independent protocols are especially relevant or cryptographic applications, as they are insensitive to hacking attacks exploiting imperfections on the modelling of the devices.   

Beyond Moore's law: towards competitive quantum devices

A century after the invention of quantum theory and fifty years after Bell's inequality we see the first quantum devices emerge as products that aim to be competitive with the best classical computing devices. While a universal quantum computer of non-trivial size is still out of reach there exist a number commercial and experimental devices: quantum random number generators, quantum simulators and quantum annealers. In this colloquium I will present some of these devices and validation tests we performed on them. Quantum random number generators use the inherent randomness in quantum measurements to produce true random numbers, unlike classical pseudorandom number generators which are inherently deterministic. Optical lattice emulators use ultracold atomic gases in optical lattices to mimic typical models of condensed matter physics. In my talk I will focus especially on the devices built by Canadian company D-Wave systems, which are special purpose quantum simulators for solving hard classical optimization problems. I will review the controversy around the quantum nature of these devices and will compare them to state of the art classical algorithms. I will end with an outlook towards universal quantum computing and end with the question: which important problems that are intractable even for post-exa-scale classical computers could we expect to solve once we have a universal quantum computer?   

Bell and Beyond: Exploring the Limits of Nonlocality

Today, nonlocality is considered a fundamental aspect of quantum mechanics. While a full loophole-free Bell test has not yet been completed, recent experiments closing the detection loophole with photons have shown that this landmark experiment is close to being realized. In addition to showing quantum mechanics is nonlocal, Bell tests can address future theories beyond quantum mechanics. For example, the chained Bell inequality can be used to limit the predictive strength of any future theory limited only by causality. In this talk, we will describe our high-quality photon entanglement source that we used to experimentally close the detection loophole, and discuss the subtleties of potential additional loopholes. In addition, we have used our source to probe the nonlocal aspects of quantum mechanics, and theories beyond quantum mechanics, by performing a plethora of unique Bell tests. We use these tests to show that entanglement and nonlocality are different resources, that no causal theory can have predictive power greater than 57$\pm $0.05{\%}, and that quantum mechanics must have a complex phase.