Geometry of quantum states: New construction of positive maps

We provide a new class of positive maps in matrix algebras. The construction is based on the family of balls living in the space of density matrices of n-level quantum system. This class generalizes the celebrated Choi map and provide a wide family of entanglement witnesses which define a basic tool for analyzing quantum entanglement. (C) 2009 Elsevier B.V. All rights reserved.