Jan-Åke Larsson

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Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell's theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell's inequalities. Previous experiments convincingly(More)
Unconditionally secure message authentication is an important part of quantum cryptography (QC). In this correspondence, we analyze security effects of using a key obtained from QC for authentication purposes in later rounds of QC. In particular, the eavesdropper gains partial knowledge on the key in QC that may have an effect on the security of the(More)
A Kochen-Specker inequality is presented, which enables a test for contextual hidden-variable models at low experimental error rates. This is achieved by formulating the concept of “probabilistic contextuality”, possible to use in non-ideal experiments. Assuming that the errors are independent, an explicit error bound of 1.057% is derived, below which a(More)
We present a formal theory of contextuality for a set of random variables grouped into different subsets (contexts) corresponding to different, mutually incompatible conditions. Within each context the random variables are jointly distributed, but across different contexts they are stochastically unrelated. The theory of contextuality is based on the(More)
This is a study taking an information theoretic approach toward quantum contextuality. The approach is that of using the memory complexity of finite-state machines to quantify quantum contextuality. These machines simulate the outcome behaviour of sequential measurements on systems of quantum bits as predicted by quantum mechanics. Of interest is the(More)
The notion of (non)contextuality pertains to sets of properties measured one subset (context) at a time. We extend this notion to include so-called inconsistently connected systems, in which the measurements of a given property in different contexts may have different distributions, due to contextual biases in experimental design or physical interactions(More)
We report on a search for mutually unbiased bases MUBs in six dimensions. We find only triplets of MUBs, and thus do not come close to the theoretical upper bound 7. However, we point out that the natural habitat for sets of MUBs is the set of all complex Hadamard matrices of the given order, and we introduce a natural notion of distance between bases in(More)