Journal of Physics A, Mathematical and Theoretical vol:41 issue:49 pages:-
A recently proposed test of quantumness Alicki and Van Ryn (2008 J. Phys. A: Math. Theor. 41 062001) is put into a broader mathematical and physical perspective. The notion of quantumness witnesses is introduced, in analogy to entanglement witnesses, and is illustrated by examples of single qubit and many-body systems with additive observables. We also compare our proposal with the quantumness test based on quantum correlations (entanglement) and Bell inequalities, and go on to discuss a class of quantumness witnesses associated with the phase-space representation of quantum mechanics.