Twisted behavior of dipolar BECs: Dipole-dipole interaction beyond the self-consistent field approximation and exchange electric dipole interaction

Dipole-dipole interaction is a long-range interaction, hence we could expect that the self-consistent field approximation might be applied. In most cases it is correct, but dipolar BECs reveal a surprise. Structure of the self-consistent field term requires that interacting particles are in different quantum states, while in BECs all particles in a single quantum state. This fact requires to consider the two-particle polarisation, which describes dipole-dipole interaction, in more details. We present this consideration and show an astonishing result that the two-particle quantum correlation in dipolar BECs reveals in the same form as the self-consistent field term.