Nonlocality, Macroscopic Realism, and Negative (Quasi)-Probabilities

Quasiprobabilities obey the usual axioms of probability, except that they may take negative values. They are familiar in quantum mechanics from, for example, the Wigner function. Another distribution function which is inspired by the decoherent histories approach can be shown to be useful in relation to locality and macroscopic realism, since the negativity may be interpreted as an indicator of nonclassicality. In other words, the distribution is formulated under the assumption of local realistic or macrorealistic hidden variables and the inconsistencies of the underlying assumption for certain parameter ranges is reflected in the sign of the quasiprobability distribution. This talk, based on a Master’s project at Imperial College London, will briefly review the differences and similarities between locality and macroscopic realism and link these to negativity of quasiprobability distributions. Finally, some partial results relating the Tsirelson bounds on Bell inequality violations to bounds on negativity will be discussed.