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– This paper analyzes effects of time-dependence in the Bell inequality. A generalized inequality is derived for the case when coincidence and non-coincidence [and hence whether or not a pair contributes to the actual data] is controlled by timing that depends on the detector settings. Needless to say, this inequality is violated by quantum mechanics and… (More)

We report on a search for mutually unbiased bases (MUBs) in 6 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)

We report on a search for mutually unbiased bases ͑MUBs͒ 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)

- Jorgen Cederlof, Jan-Åke Larsson
- IEEE Transactions on Information Theory
- 2008

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)

The simulation of quantum effects requires certain classical resources, and quantifying them is an important step in order to understand the difference between quantum and classical physics. We investigate the minimum classical memory needed to simulate the phenomenon of state-independent quantum contextuality in sequential measurements. We derive optimal… (More)

- Janne V Kujala, Ehtibar N Dzhafarov, Jan-Åke Larsson
- Physical review letters
- 2015

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)

- Jan-Åke Larsson
- Quantum Information & Computation
- 2002

Quantum Cryptography, or more accurately, Quantum Key Distribution (QKD) is based on using an unconditionally secure " quantum channel " to share a secret key among two users. A manufacturer of QKD devices could, intentionally or not, use a (semi-)classical channel instead of the quantum channel, which would remove the supposedly unconditional security. One… (More)

- Mirsad Cirkic, Daniel Persson, Erik G. Larsson, Jan-Åke Larsson
- 2011 IEEE International Conference on Acoustics…
- 2011

We derive a Gaussian approximation of the LLR distribution conditioned on the transmitted signal and the channel matrix for the soft-output via partial marginalization MIMO detector. This detector performs exact ML as a special case. Our main results consist of discussing the operational meaning of this approximation and a proof that, in the limit of high… (More)

- Aysajan Abidin, Jan-Åke Larsson
- WEWoRC
- 2011

- Matthias Kleinmann, Costantino Budroni, Jan-Åke Larsson, Otfried Gühne, Adán Cabello
- Physical review letters
- 2012

Contextuality is a natural generalization of nonlocality which does not need composite systems or spacelike separation and offers a wider spectrum of interesting phenomena. Most notably, in quantum mechanics there exist scenarios where the contextual behavior is independent of the quantum state. We show that the quest for an optimal inequality separating… (More)