Multiqubit UPB: the method of formally orthogonal matrices
Lin Chen, Dragomir Ž. Djoković · Journal of Physics A Mathematical and Theoretical · 2018
Abstract We use formal matrices whose entries we view as vector variables taking unit vector values in one-qubit Hilbert spaces of a multiqubit quantum system. We construct many unextendible product bases (UPBs) of new sizes in such systems and provide a new construction of UPBs of n qubits of cardinality n + 1 when . We also give a new method of constructing multiqubit entangled states with all partial transposes positive.