Anton Zeilinger / Quanten-Teleportation / ISBN 3-85160-035-5

Disagreements about the philosophical implications of quantum theory are as old as the theory itself. Experiments which could previously only take place in the head can now be performed in the laboratory. This has resulted in a better understanding of the nature and peculiarities of quantum theory whilst also laying the foundation stone for a new form of information technology. For the crew of the “Spaceship Enterprise”, beaming has long been routine: a team simply steps onto the transporter chamber to explore an unknown planet. Lights pulsate, strange noises sound, the forms of the intrepid space travellers dissolve – and reappear immediately on the planet’s surface. If this vision of so-called teleportation were realisable, there would be no need for arduous long-haul flights with several onboard meals. Although the beaming of large objects or living people will remain in the realm of pure fantasy for a long time to come, the quantum teleportation of single photons has already been successfully performed in the laboratory. Quantum teleportation utilises certain fundamental – and extremely strange – anomalies of quantum mechanics, a branch of physics developed in the first quarter of the 20th century to explain atomic processes. From the very beginning, theorists recognised that quantum physics leads to a multitude of new phenomena, which often diametrically contradict everyday experience. Due to technical advances towards the end of the 20th century, research scientists could carry out experiments which not only demonstrated the fundamental and often bizarre aspects of quantum mechanics but also made previously unimaginable “feats” possible In science fiction stories teleportation permits arbitrary distances to be instantly overcome and thereby overthrows a basic principle of Einstein’s theory of relativity, where nothing can travel faster than light (see Raymond Y. Chiao „ Schneller als Licht? “, in Spektrum der Wissenschaft 10/1993, p. 40). Teleportation is at any rate a lot less tedious than the more usual forms of space travel. Apparently Gene Roddenberry, the creator of the television series Star Trek, invented the transporter beam to save on the costs of filming take-off and landing manoeuvres on alien planets. Although in the science fiction genre the procedure of beaming varies from one story to another, the principal is basically as follows: an apparatus completely analyses the object concerned and collects all the necessary descriptive information. This data is transmitted to a receiving station, where a new original is created from it. Sometimes the material which made up the original is transported to the transceiver receiving station, perhaps in the form of energy; in other cases the copy is created from atoms and molecules which are already present at the receiver site. Quantum mechanics appears of course to deny the possibility of such a procedure. The Heisenberg Uncertainty Principle (HUP) states that it is never possible to pinpoint the exact place or impulse of an object. Therefore the object to be teleported could not be analysed exactly; the position and speed of each atom and electron are always shrouded with uncertainty. Heisenberg’s principle is also valid for other pairs of measurement categories and denies all in all the possibility to completely and exactly measure the total quantum state of an object. How-ever, precisely that would be necessary to get all the data required to describe the original. In 1993 some physicists threw this theory out of the window by discovering a means of harnessing quantum mechanics itself for teleportation. Charles H. Bennett of IBM, Gilles Brassard, Claude Crépeau and Richard Josza of University of Montréal (Canada). Asher Peres of Technion, the Israel Institute of Technology, and William K. Wootters of William College (Massachusetts) discovered that a strange yet fundamental characteristic of quantum mechanics – the so-called entaglement – can serve to bypass the limitations set out in Heisen-berg’s uncertainty principle without breaking it.

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Anton Zeilinger ist Professor der Experimentalphysik an der Universität Wien. Seine Forschungstätigkeit konzentriert sich auf Experimente mit Photonen, Neutronen, Atomen und seit kurzem großen Molekülen. Für weltweites Aufsehen sorgte die erste Realisierung der Quantenteleportation.