Alice has made a decision in her mind. While she does not want to reveal it to Bob at this moment, she would like to convince Bob that she is committed to this particular decision and that she cannot change it at a later time. Is there a way to get Bob's trust? This practical question is also one of the fundamental dilemmas of quantum cryptography, and is discussed in this fascinating and highly topical volume. In addition, experimental realizations and theoretical aspects of trapped-ion and other possible quantum computers are presented in detail. Still a number of years ahead, quantum computers will possibly shape the 21st century as much as conventional computers shaped the 20th century. This volume provides you with up-to-date information on the current state of the art in this rapidly advancing field.About the Author: Professor Samuel L. Braunstein Reader at the School of Informatics, University of Wales, Bangor. Member of UK Quantum Optics & Computation Networks Member of the ESF Quantum Information Theory program. Expert in the field of Quantum Optics und Quantum Computing.