[1] Institut de Physique de la Matière Complexe, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
[2] Optical Sciences Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SE, Washington, DC 20375, United States
[3] Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 31235, United States
[4] Institute of Neurobiology and Molecular Medicine, 00133 Rome, Italy
[5] Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, United States
[6] Istituto di Stuttura della Materia, via Fosso del Cavaliere 100, 00133 Rome, Italy