Cohomological invariants of Abelian symplectic quotients of pure $r$-qubits

Abstract

In this paper, we study cohomology rings and cohomological pairings over Abelian symplectic quotients of special Hamiltonian tori manifolds. The Hamiltonian group actions appear in quantum information theory where the tori are maximal tori of some compact semi-simple Lie groups, so called the Local Unitary groups, which act effectively and with non-trivial characters on specific complex projective varieties. The complex projective spaces are in fact spaces of pure multi-partite quantum states. By studying the geometry of associated moment polytopes, we explicitly obtain cohomology rings, in terms of elementary symmetric functions, and a recursive wall-crossing algorithm to compute cohomological pairings over the corresponding Abelian symplectic quotients. We propose algorithms for general $r$-qubit case and elaborate discussions with explicit examples for the cases with $r=2,3$.