Strong Kantorovich duality for quantum optimal transport with generic cost and optimal couplings on quantum bits

Abstract: We prove Kantorovich duality for a linearized version of a recently proposed non-quadratic quantum optimal transport problem, where quantum channels realize the transport. As an application, we determine optimal solutions of both the primal and the dual problem using this duality in the case of quantum bits and distinguished cost operators, with certain restrictions on the states involved. Finally, we use this information on optimal solutions to give an analytical proof of the triangle inequality for the induced quantum Wasserstein divergences.