[1] Queens Univ Belfast, Ctr Quantum Mat & Technol, Sch Math & Phys, Belfast BT7 1NN, North Ireland
[2] Univ Palermo, Dipartimento Fis & Chim Emilio Segre, via Archirafi 36, I-90123 Palermo, Italy
[3] Univ Trieste, Dept Phys, Str Costiera 11, I-34151 Trieste, Italy
[4] Ist Nazl Fis Nucl, Trieste Sect, I-34127 Trieste, Italy