1. Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA.
2. Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089, USA.
3. Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
4. IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA.