Anton Zeilinger (; born 20 May 1945) is an Austrian quantum physicist and Nobel laureate in physics of 2022. Zeilinger is professor of physics emeritus at the University of Vienna and senior scientist at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences. Most of his research concerns the fundamental aspects and applications of quantum entanglement.

In 2007, Zeilinger received the first Inaugural Isaac Newton Medal of the Institute of Physics, London, 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".

Early life and education

Anton Zeilinger was born in 1945 in Ried im Innkreis, Upper Austria, Austria. He studied physics at the University of Vienna from 1963 to 1971. He received a doctorate from the University of Vienna in 1971, with a thesis on "Neutron depolarization measurements on a Dy-single crystal" under Helmut Rauch. He qualified as a university lecturer (habilitation) at the Vienna University of Technology in 1979.

Career

In the 1970s, Zeilinger worked at the Vienna Atominstitut as a research assistant and later as an associate researcher at the Massachusetts Institute of Technology Neutron Diffraction Laboratory until 1979, when he accepted the position of assistant professor at the same Atominstitut. That year he qualified as a university professor at the Vienna University of Technology.

In 1981 Zeilinger returned to MIT, as an associate professor on the physics faculty, until 1983. Between 1980 and 1990 he worked as a professor at the Vienna University of Technology, the Technical University of Munich, the University of Innsbruck and the University of Vienna.

Since 2006, Zeilinger is the vice chairman of the board of trustees of the Institute of Science and Technology Austria, an ambitious project initiated by Zeilinger's proposal. In 2009, he founded the International Academy Traunkirchen, which is dedicated to the support of gifted students in science and technology. He is a fan of the Hitchhiker's Guide To The Galaxy by Douglas Adams, going so far as to name his sailboat 42.

Research

<!--Zeilinger works in the foundations of quantum mechanics. He discovered, together with Daniel Greenberger and Michael Horne, novel counter-intuitive features of three- and four-particle states. He was the first, with his team, to realize those in experiment. This opened the field of multi-particle interference and multi-particle quantum correlations. Using the methods developed there, he performed the first quantum teleportation of an independent qubit. This was followed by the realization of entanglement swapping, a most interesting concept where an entangled state is teleported.

This work was followed by numerous tests of Bell's inequalities, including a Cosmic Bell Test. Other fundamental experiments concerned Leggett's nonlocal realistic theories, tests of quantum contextuality in Kochen-Specker experiments, and experiments on nonlocal Schrödinger steering with entangled states.

Many of these results became relevant in the development of quantum information technology, where he also performed pioneering experiments. His experiment on quantum dense coding was the first using entanglement to demonstrate a primitive, not possible in classical physics. He also realized the first entanglement-based quantum cryptography experiment and later, quantum communication over increasing distances and, implementing higher-dimensional states, with increasing information capacity. Possible applications also include one-way quantum computation and blind quantum computation. Among his further contributions to the experimental and conceptual foundations of quantum mechanics are matter wave interference all the way from neutrons via atoms to macromolecules such as fullerenes.-->

Quantum teleportation

Zeilinger published one of the first realizations of quantum teleportation of an independent qubit. He later expanded this work to developing a source for freely propagating teleported qubits and quantum teleportation over 144 kilometers between two Canary Islands. Quantum teleportation is an essential concept in many quantum information protocols. Besides its role for the transfer of quantum information, it is also considered as an important possible mechanism for building gates within quantum computers.

Entanglement swapping – teleportation of entanglement

Entanglement swapping is the teleportation of an entangled state. After its proposal, entanglement swapping was first realized experimentally by Zeilinger's group in 1998. It was then applied to carry out a delayed-choice entanglement swapping test. <!--Entanglement swapping is the crucial ingredient for quantum repeaters which are expected to connect future quantum computers.-->

Entanglement beyond two qubits – GHZ-states and their realizations

thumb|Anton Zeilinger holding a sculpture by [[Julian Voss-Andreae, photo by J. Godany]]

Anton Zeilinger contributed to the opening up of the field of multi-particle entanglement. In 1990, he was the first with Daniel Greenberger and Michael Horne to work on entanglement of more than two qubits. 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.

GHZ states were the first instances of multi-particle entanglement ever investigated. <!--Surprisingly, multi-particle entangled states exhibit qualitatively different properties compared to two-particle entanglement. In the 1990s, it became the main goal of Zeilinger's research to realize such GHZ states in the laboratory, which required the development of many new methods and tools.-->

Finally, in 1999, he succeeded in providing the first experimental evidence of entanglement beyond two particles and also the first test of quantum nonlocality for GHZ states. <!--He also was the first to realize that there are different classes of higher-dimensional entangled states and proposed W-states. Today, multi-particle states have become an essential workhorse in quantum computation and thus, GHZ-states have even become an individual entry in the PACS code.-->

Quantum communication, quantum cryptography, quantum computation

<!--In 1996, Anton Zeilinger with his group realized hyper-dense coding. There, one can encode into one qubit more than one classical bit of information. This was the first realization of a quantum information protocol with an entangled state, where one is able to achieve something impossible with classical physics.-->

In 1998 (published in 2000), his group was the first to implement quantum cryptography with entangled photons. he performed the first implementation of one-way quantum computation. This is a protocol based on quantum measurement as proposed by Knill, Laflamme and Milburn. <!--Most recently, it has been shown that one-way quantum computation can be used to implement blind quantum computing. This solves a problem in Cloud computing, namely that, whatever algorithm a client employs on a quantum server is completely unknown, i.e. blind, to the operator of the server.-->

The experiments of Zeilinger and his group 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 over 144&nbsp;km between two Canary Islands, resulting in a successful demonstration that quantum communication with satellites is feasible. His dream is to put sources of entangled light onto a satellite in orbit.

Further novel entangled states

With his group, Anton Zeilinger made many contributions to the realization of novel entangled states. The source for polarization-entangled photon pairs developed with Paul Kwiat when he was a PostDoc in Zeilinger's group is used in many laboratories. The first demonstration of entanglement of orbital angular momentum of photons opened up a new field of research in many laboratories.

Macroscopic quantum superposition

Zeilinger is also interested to extend quantum mechanics into the macroscopic domain. In the early 1990s, he 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 part 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 these C<sub>60</sub> and C<sub>70</sub> molecules 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 .-->

In 2005, Zeilinger with his group investigated the quantum physics of mechanical cantilevers. In the year 2006 along with Heidmann in Paris and Kippenberg in Garching they demonstrated 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.-->

Using orbital angular momentum states, he was able to demonstrate entanglement of angular momentum up to 300 ħ.

Further fundamental tests

Zeilinger's program of fundamental tests of quantum mechanics is aimed at implementing experimental realizations of many non-classical features of quantum physics for individual systems. In 1998, he provided the final test of Bell's inequality closing the communication loophole by using superfast random number generators. His group also realized the first Bell inequality experiment implementing the freedom-of-choice condition and provided the first realization of a Bell test without the fair sampling assumption for photons. <!--All these experiments are not only of fundamental interest, but also important for quantum cryptography. In 2015, at the same time as the group of Ronald Hanson at Delft University of Technology and the group of Sae-Woo Nam at the National Institute of Standards and Technology (NIST), Zeilinger's group closed the locality and detection loopholes in Bell experiments, thereby corroborating quantum mechanics and ruling out theories that satisfy local causality and providing definitive proof that quantum cryptography can be unconditionally secure.-->

Among the further fundamental tests he performed the most notable one is his test of a large class of nonlocal realistic theories proposed by Leggett. The group of theories excluded by that experiment can be classified as those which allow reasonable subdivision of ensembles into sub-ensembles. It 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 Leggett inequality was shown to be violated in the experiments of the Zeilinger group.

In an analogous way, his group showed that even quantum systems where entanglement is not possible exhibit non-classical features which cannot be explained by underlying non-contextual probability distributions.

Neutron interferometry

Anton Zeilinger's earliest work is perhaps his least known. His work on neutron interferometry has provided a foundation for his later research. 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), 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. Zeilinger built a double-slit diffraction experiment on the S18 instrument at the Institut Laue-Langevin which, later on, gained in accuracy and could act with only one neutron at a time in the apparatus.

Honours and awards

International prizes and awards

  • Nobel Prize in Physics (2022, with John Clauser, Alain Aspect)
  • Micius Quantum Prize, Micius Quantum Foundation (2019, with Stephen Wiesner, Charles H. Bennett, Gilles Brassard, Artur Ekert and Pan Jianwei)
  • Cozzarelli Prize in Physical and Mathematical Sciences, PNAS and National Academy of Sciences (2018, with Alexey A. Melnikov, Hendrik Poulsen Nautrup, Mario Krenn, Vedran Dunjko, Markus Tiersch and Hans Briegel)
  • John Stewart Bell Prize for Research on Fundamental Issues in Quantum Mechanics and their Applications, University of Toronto (2017, with Ronald Hanson and Sae Woo Nam)
  • Silver medal of the Senate of the Czech Republic (2017)
  • Fellow of the American Association for the Advancement of Science (elected 2012)
  • Wolf Prize in Physics, Wolf Foundation (2012, with Alain Aspect and John Clauser)
  • Grand Merit Cross with Star of the Order of Merit of the Federal Republic of Germany (2009)
  • Inaugural Isaac Newton Medal, Institute of Physics (2008)
  • Quantum Electronics Prize, European Physical Society (2007)
  • King Faisal International Prize in physics, King Faisal Foundation (2005)
  • Descartes Prize, European Union, as member of the IST-QuComm project collaboration (2004)
  • Klopsteg Memorial Award, American Association of Physics Teachers (2004)
  • Order Pour le Mérite for Arts and Sciences (2000)
  • European Optics Prize, European Optical Society (1996)

Austrian prizes and awards

  • Grand Decoration of Honour in Gold with Sash for Services to the Republic of Austria (2024)
  • Austrian Decoration for Science and Art, Republic of Austria (2001)

Zeilinger has been interviewed by Morgan Freeman in season 2 of Through the Wormhole.

References

  • Curriculum Vitae of Anton Zeilinger
  • Quantum Teleportation by Zeilinger, 2003 update of 2000 Scientific American article
  • Spooky action and beyond an interview with Anton Zeilinger at signandsight.com
  • The lecture delivered by Professor Anton Zeilinger as the inaugural recipient of the Isaac Newton Medal, Institute of Physics, 17 June 2008, [http://www.iop.org/activity/awards/International%20Award/page_31978.html] (68 min 25 sec). <br />Note: On the page linked, a second video is accommodated which shows Professor Zeilinger speaking amongst others about his personal life.
  • Anton Zeilinger on the opening panel discussion at the Quantum to Cosmos festival at Perimeter Institute with Katherine Freese, Leo Kadanoff, Lawrence Krauss, Neil Turok, Sean M. Carroll, Gino Segrè, Andrew White, and David Tong.
  • Homepage of the International Academy Traunkirchen
  • Es stellt sich letztlich heraus, dass Information ein wesentlicher Grundbaustein der Welt ist , a German-language interview with Zeilinger by Andrea Naica-Loebell