Fig. 2: Comparison of polytopes for three and four qubits.
From: Open quantum system violates generalized Pauli constraints on quantum device
Polytopes showing the sets of three lowest natural occupations, ordered from highest to lowest, for the three-qubit system (a) and for the four-qubit system (b), measured on ibmq_jakarta. The sets of occupations lying inside the yellow region of the polytope are compatible with at least one closed (pure-state) quantum system. Sets of natural occupations that lie in the blue region of the polytope are only compatible with an open (ensemble) quantum system. Addition of a single environmental qubit to the closed three-qubit system results in the violation of the generalized Pauli constraints (GPCs) and allows the quantum system to reach openness.
