In quantum teleportation it is possible to transfer the complete information carried by a system over to another system without the information travelling along any identifiable path. While such an identifiable path exists in all methods of communication known to mankind thus far, in quantum teleportation the information a system carries is transferred directly.

This is accomplished by applying entanglement, a counterintuitive feature of the quantum world. In entanglement one has two or more systems coupled in a way much stronger than classical systems can be, or much stronger than common sense would permit. The essence of entanglement is that the systems entangled with each other can jointly have well-defined characteristics, while the individual systems can be completely random without carrying any well-defined information on their own.

When quantum teleportation succeeds, the new system then becomes completely identical with the original and the original by necessity has to disappear. This latter feature is a consequence of the quantum no-cloning theorem which states that it is not possible at all that a quantum system can perfectly be cloned. The no-cloning theorem is closely related to the fact that no information can travel faster than light which is a central tenet of modern physics following Albert Einstein.

The quantum teleportation experiment raises very deep questions about the nature of reality at the quantum level. It shows that information, or knowledge, in some instances can have a more fundamental meaning than an objective reality. To be more specific, what can be said, i.e. information, can define what can be reality. What changes during a measurement is the quantum state. If, as is often the case, the quantum state is taken too realistically, all sorts of conundrums and puzzles emerge, the most famous one being Schroedinger's cat paradox. Yet, if the quantum state is taken to be just the representation of knowledge then all paradoxa disappear.

This point of view also offers a solution to the puzzle of the role of the observer. In quantum physics the observer, by choosing the measurement apparatus, can decide which of many complementary aspects of a phenomenon can actually become reality. Yet, most importantly, the specific result obtained remains completely random and hence outside the reach of the influence of the observer. On a much deeper level we may say that reality itself is beyond our reach. We can only concern ourselves with what can be said about reality.


Anton Zeilinger and his group - one of the world's leading experimental quantum physics research groups; have realized in experiment many fundamental predictions of quantum theory and so proved their amazing consequences for our view of the world. This experimental realization has also laid the foundation for completely new forms of technology, such as the fields of like quantum cryptography, quantum computation and quantum information processing. His most recent major achievements include the world's first quantum teleportation (1997), the first demonstration of entanglement of more than two particles (Greenberger-Horne-Zeilinger states, 1998), the observation of quantum interference for fullerenes, the most massive and complex objects to date (1999), the first realization of quantum cryptography (1999) and the first verification of entanglement of four particles (2000). Anton Zeilinger was born 1945 in Austria and has held professorships at the Universities of Munich, Vienna, Innsbruck, Melbourne, at MIT and the Collége de France. Among his many awards and prizes are an honorary professorship at the University of Science and Technology of China, memberships of the German order Pour le Mérite and of the Academia Scientiarum et Artium Europaea, and the Senior Humboldt Fellow Prize of the Alexander von Humboldt-Stiftung. He is Director of the Institute of Experimental Physics at the University of Vienna.