Geometry of the set of mixed quantum states: An apophatic approach

Abstract

The set of quantum states consists of density matrices of order $N$, which are hermitian, positive and normalized by the trace condition. We analyze the structure of this set in the framework of the Euclidean geometry naturally arising in the space of hermitian matrices. For N=2 this set is the Bloch ball, embedded in ${\mathbb{R}}^3$. For $N\ge 3$ this set of dimensionality $N^2-1$ has a much richer structure. We study its properties and at first advocate an apophatic approach, which concentrates on characteristics not possessed by this set. We also apply more constructive techniques and analyze two dimensional cross-sections and projections of the set of quantum states. They are dual to each other. At the end we make some remarks on certain dimension dependent properties.

13 pages, 12 figures, v2: 5 figures changed from bw to color

References in corpus (6)

• Geometry of the generalized Bloch sphere for qutrits
• Geometry of quantum systems: density states and entanglement
• The structure of reversible computation determines the self-duality of quantum theory
• Construction, classification and parametrization of complex Hadamard matrices
• Numerical shadow and geometry of quantum states
• Dualities in Convex Algebraic Geometry

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