# Anton Zeilinger

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Anton Zeilinger

Infobox Scientist
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name = Anton Zeilinger

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caption = Anton Zeilinger (photo credit: J. Godany)
birth_date = 20 May 1945
birth_place = Ried im Innkreis, Austria
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residence = flag|Austria
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nationality = flag|Austria|name=Austrian
ethnicity =
fields = Physicist
workplaces = University of Vienna
Technical University of Munich
Technical University of Vienna
Massachusetts Institute of Technology
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notable_students =
known_for = Quantum teleportation
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awards = Newton Prize (2007)
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Anton Zeilinger (born on 20 May 1945 in Ried im Innkreis, Austria) is an Austrian quantum physicist. He is currently professor of physics at the University of Vienna, previously University of Innsbruck. He is also the director of the Vienna branch of the Institute for Quantum Optics and Quantum Information IQOQI at the Austrian Academy of Sciences. Zeilinger has been called a pioneer in the new field of quantum information and is renowned for his realization of quantum teleportation with photons.

Biography

Anton Zeilinger, born 1945 in Austria, has held positions at the University of Innsbruck, the Technical University of Munich, the Technical University of Vienna and at the Massachusetts Institute of Technology (MIT) and distinguished visiting positions at Humboldt University in Berlin, Merton College of Oxford University and the Collége de France in Paris. Zeilinger received many awards for his scientific work, among the most recent being the King Faisal Prize (2005), and the first Newton Prize of the IOP (2007). He is a member of six Scientific Academies. Anton Zeilinger is currently Professor of Physics at the University of Vienna and Scientific Director of the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences. He is a fan of the Hitchhiker's Guide To The Galaxy by Douglas Adams, going so far as to name his sailboat 42 cite journal|title=The Gedanker Experimenter|journal=Scientific American|date=2007-08-01|first=JR|last=Minkel|coauthors=|volume=|issue=|pages=|id= |url=http://www.sciam.com/article.cfm?chanID=sa006&articleID=ABBA5449-E7F2-99DF-3ACFAC15B16FEC60&colID=30|format=|accessdate=2008-01-17 ] .

Work

Anton Zeilinger’s achievements have been most succinctly described in his citation for the Isaac Newton Medal of the Institute of Physics (UK): “For his pioneering conceptual and experimental contributions to the foundations of quantum physics, which have become the cornerstone for the rapidly-evolving field of quantum information.”

Neutron interferometry

As a member of the group of his thesis supervisor, Helmut Rauch, at the Technical University of Vienna, Zeilinger participated in a number of neutron interferometry experiments at the Institut Laue-Langevin (ILL) in Grenoble. His first such experiment already confirmed a fundamental prediction of quantum mechanics, the sign change of a spinor phase upon rotation. This was followed by the first experimental realization of coherent spin superposition of matter waves. He continued his work in neutron interferometry at MIT with C.G. Shull (Nobel Laureate 1995) focusing specifically on dynamical diffraction effects of neutrons in perfect crystals which are due to multi-wave coherent superposition. After his return to Europe, he built up an interferometer for very cold neutrons which preceded later similar experiments with atoms. The fundamental experiments there included a most precise test of the linearity of quantum mechanics and a beautiful double-slit diffraction experiment with only one neutron at a time in the apparatus. Actually, in that experiment, while one neutron was registered, the next neutron still resided in its Uranium nucleus waiting for fission to happen.

Quantum entanglement

In the late 1980s, Anton Zeilinger became interested in quantum entanglement. This work resulted in his most significant accomplishments and opened up the new fields of quantum teleportation, quantum information, quantum communication and quantum cryptography.

Together with Daniel Greenberger and Michael Horne, Zeilinger wrote the first paper ever on entanglement beyond two particles. The resulting GHZ theorem (see Greenberger-Horne-Zeilinger state) is fundamental for quantum physics, as it provides the most succinct contradiction between local realism and the predictions of quantum mechanics. Also, GHZ states were the first instances of multi-particle entanglement ever investigated. Such states have become essential in quantum information science. GHZ states are now even an individual entry in the PACS code.

As a professor at the University of Innsbruck, Zeilinger started experiments on entangled photons. His goal from the early 1990s on, to demonstrate the GHZ contradiction, was achieved finally in 1998.

Along the road, Zeilinger developed many novel tools for entangled photon physics, for example a bright source for polarization-entangled photons, ways to identify Bell states and methods for producing coherent emission of more than one entangled pair from one crystal. The resulting technology allowed him to perform a number of first quantum information experiments with entangled photons. The first ever use of entanglement in any quantum information protocol was his demonstration of hyperdense coding. His achievements also include the first entanglement-based quantum cryptography, the first quantum teleportation experiment of an independent photon, the first realization of entanglement swapping and an experiment closing the communication loophole in a test of Bell’s inequality.

Since 2000, Anton Zeilinger’s research focused on all-optical quantum computation, the development of entanglement-based quantum cryptography systems, and experiments with entangled photon pairs over very large distances. In all-optical quantum computation, Zeilinger with his group were the first to demonstrate a number of basic procedures, like entanglement purification and certain quantum gates. This culminated in the first demonstrations of one-way quantum computation, including most recently, ultra-fast active feed-forward. The one-way quantum computation scheme was used to realize Grover’s search algorithm and various quantum games, including prisoner’s dilemma.

In quantum cryptography, Zeilinger’s group is developing a prototype in collaboration with industry. While most of the community was working on the much easier scheme of using weak laser pulses, Zeilinger based his approach exclusively on the more demanding scheme using entangled photons. A recent proof that entanglement is a necessary condition for the security of the quantum channel confirms that this choice is correct.

Zeilinger’s experiments on the distribution of entanglement over large distances began with both free-space and fiber-based quantum communication and teleportation between laboratories located on the different sides of the river Danube. This was then extended to larger distances across the city of Vienna and most recently over 144 km between two Canary Islands, resulting in a successful demonstration that quantum communication with satellites is feasible. His dream was to bounce entangled light off of satellites in orbit. This was achieved during an experiment at the Italian Matera Laser Ranging Observatory. [ [http://arxiv.org/abs/0803.1871v1 [0803.1871v1 Experimental verification of the feasibility of a quantum channel between Space and Earth ] ]

An important fundamental spin-off of these experiments was the first test in 2007 of a non-local realistic theory proposed by Leggett which goes significantly beyond Bell’s theorem. While Bell showed that a theory which is both local and realistic is at variance with quantum mechanics, Leggett considered nonlocal realistic theories where the individual photons are assumed to carry polarization. The resulting inequality was shown to be violated in the experiments of the Zeilinger group.

Atom and macromolecule interferometry

Parallel with his work on quantum entanglement with photons, Anton Zeilinger in the early 1990s started experiments in the field of atom optics. He developed a number of ways to coherently manipulate atomic beams, many of which, like the coherent energy shift of an atomic De Broglie wave upon diffraction at a time-modulated light wave, have become cornerstones of today’s ultracold atom experiments.

In 1999, Zeilinger abandoned atom optics for experiments with very complex and massive macro-molecules - fullerenes. The successful demonstration of quantum interference for $C_\left\{60\right\}$ and $C_\left\{70\right\}$ molecules (fullerenes) in 1999 opened up a very active field of research. Key results include the most precise quantitative study to date of decoherence by thermal radiation and by atomic collisions and the first quantum interference of complex biological macro-molecules. This work is continued by Markus Arndt.

Quantum optomechanics

In 2005, Zeilinger with his group again started a new field, the quantum physics of mechanical cantilevers. The group was the first to demonstrate experimentally the self-cooling of a micro-mirror by radiation pressure, that is, without feedback. That phenomenon can be seen as a consequence of the coupling of a high-entropy mechanical system with a low-entropy radiation field. This work is now continued independently by Markus Aspelmeyer.

ee also

* Quantum Aspects of Life

References

* [http://www.quantum.at/zeilinger/ Zeilinger's homepage]
* [http://www.univie.ac.at/qfp/publications3/pdffiles/2003-24.pdf "Quantum Teleportation" by Zeilinger] , 2003 update of 2000 Scientific American article
* [http://www.heise.de/tp/deutsch/inhalt/lis/7550/1.html Es stellt sich letztlich heraus, dass Information ein wesentlicher Grundbaustein der Welt ist] , a German-language interview with Zeilinger by Andrea Naica-Loebell
* [http://www.signandsight.com/features/614.html "Spooky action and beyond"] an interview with Anton Zeilinger at signandsight.com

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