title: Quantum Brachistochrone problem and the geometry of the state space in pseudo-Hermitian quantum mechanics.
abstract: A non-Hermitian operator with a real spectrum and a complete set of eigenvectors may serve as the Hamiltonian operator for a unitary quantum system provided that one makes an appropriate choice for the defining the inner product of physical Hilbert state. We study the consequences of such a choice for the representation of states in terms of projection operators and the geometry of the state space. This allows for a careful treatment of the quantum Brachistochrone problem and shows that it is indeed impossible to achieve faster unitary evolutions using PT-symmetric or other non-Hermitian Hamiltonians than those given by Hermitian Hamiltonians.
authors.affiliation: Department of Mathematics, Koç University, Sariyer 34450, Istanbul, Turkey. amostafazadeh@ku.edu.tr
authors.forename: Ali
authors.initials: A
authors.lastname: Mostafazadeh