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Some examples of trapped surfaces
Ingemar Bengtsson
We present some simple pen and paper examples of trapped surfaces in order to help visualising this key concept of the theory of gravitational collapse. We collect these examples f…
Geometry of the set of mixed quantum states: An apophatic approach
Ingemar Bengtsson, Stephan Weis, Karol Życzkowski
The set of quantum states consists of density matrices of order , which are hermitian, positive and normalized by the trace condition. We analyze the structure of this set in th…
A Kochen-Specker inequality from a SIC
Ingemar Bengtsson, Kate Blanchfield, Adan Cabello
Yu and Oh [1] have given a state independent proof of the Kochen-Specker theorem in three dimensions using only 13 rays. The proof consists of showing that a non-contextual hidden…
Trapped surfaces
José M. M. Senovilla
I review the definition and types of (closed) trapped surfaces. Surprising global properties are shown, such as their "clairvoyance" and the possibility that they enter into flat p…
From SICs and MUBs to Eddington
Ingemar Bengtsson
This is a survey of some very old knowledge about Mutually Unbiased Bases (MUB) and Symmetric Informationally Complete POVMs (SIC). In prime dimensions the former are closely tied…
The monomial representations of the Clifford group
D. M. Appleby, Ingemar Bengtsson, Stephen Brierley +3
We show that the Clifford group - the normaliser of the Weyl-Heisenberg group - can be represented by monomial phase-permutation matrices if and only if the dimension is a square n…