1. Department of Physics and Institute for Quantum Studies, Texas A&M University, TX 77843, USA.
2. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
3. Department of Electronics, Quaid-i-Azam University, Islamabad, Pakistan.
4. Physical Research Laboratory, Navrangpura, Ahmedabad-380009, India.