OPEN SYSTEMS IN CONTACT WITH A FERROMAGNETIC FERMI SEA - QUANTUM PARTICLE-NUMBER FLUCTUATIONS

We study the effects of the particle-number fluctuation in small fermionic quantum systems in contact with a completely ferromagnetic Fermi sea in an exact diagonalization approach based on a formalism previously developed by Artacho and Falicov [Phys. Rev, B 47 (1993) 1190]. A symmetry associated with the particle-number fluctuation is identified and used, together with other symmetries of the system, in the projection of the eigenstates and the block diagonalization of the Hamiltonian matrix. A two-site Hubbard model is used as an example to illustrate the implementation of the theory. Physical consequences of the quantum particle-number fluctuation and further applications of the theoretical approach are discussed.