Nonlocality with quantum inputs: fair-sampling assumption, post-selection, and the detection-loophole.

In this seminar, we look at how one can use certain properties of quantum physics to bypass the fair-sampling assumption commonly used in most practical Bell experiments. Our approach is based on an alternative nonlocality framework called “semi-quantum nonlocality”, where measurement instructions are represented by quantum inputs instead of classical inputs. A key feature of this framework is that all “entangled states are nonlocal”, in the sense that for any entangled state there is always a semi-quantum Bell inequality with which violation can be achieved. Building on this framework, we present a semi-quantum version of the CHSH inequality whose post-selected local bound is independent of the detection loss. We will then use this inequality as an example to illustrate how quantum inputs may be used to relax the fair-sampling assumption and hence close the detection-loophole.