Anton Zeilinger

Most widely known is his first realization of quantum teleportation of an independent qubit.[8] He later expanded this work to developing a source for freely propagating teleported qubits[9] and quantum teleportation over 144 kilometers between two Canary Islands.[10] 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 is the teleportation of an entangled state. After its proposal,[11] entanglement swapping has first been realized experimentally by Zeilinger's group in 1998.[12] It was then applied to carry out a delayed-choice entanglement swapping test.[13] Entanglement swapping is the crucial ingredient for quantum repeaters which are expected to connect future quantum computers.

Anton Zeilinger contributed decisively to the opening up of the field of multi-particle entanglement.[14] In 1990, he was the first with Daniel Greenberger and Michael Horne to work on entanglement of more than two qubits.[15] The resulting GHZ theorem[16] (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.[17] 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[18] and also the first test of quantum nonlocality for GHZ states.[19] 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.

In 1996, Anton Zeilinger with his group realized hyper-dense coding.[20] 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),[21] his group was the first to implement quantum cryptography with entangled photons. Zeilinger's group is now also developing a quantum cryptography prototype in collaboration with industry.

He then also applied quantum entanglement to optical quantum computation, where in 2005,[22] 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.[23] Most recently, it has been shown[24] 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.[25] This was then extended to larger distances across the city of Vienna[26] and over 144 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.[7] A first step was achieved during an experiment at the Italian Matera Laser Ranging Observatory.[27]

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[28] became a workhorse in many laboratories worldwide. The first demonstration of entanglement of orbital angular momentum of photons[29] opened up a new burgeoning field of research in many laboratories.

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 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 these C₆₀ and C₇₀ molecules[30] 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.

In 2005, Zeilinger with his group again started a new field, the quantum physics of mechanical cantilevers. The group was the first – in the year 2006 along with work from Heidmann in Paris and Kippenberg in Garching – to demonstrate experimentally the self-cooling of a micro-mirror by radiation pressure, that is, without feedback.[31] 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.[32]

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,[33] 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[34] and provided the first realization of a Bell test without the fair sampling assumption for photons.[35] 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,[36] 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.[37] 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.[38]

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.[39] It is expected that these latter experiments will also open up novel ways for quantum information.

Anton Zeilinger's earliest work is perhaps his least known. His work on neutron interferometry has provided an important foundation for his later research achievements. 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 very first such experiment confirmed a fundamental prediction of quantum mechanics, the sign change of a spinor phase upon rotation.[40] 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 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.

Then, as a professor at the University of Innsbruck, Zeilinger started experiments on entangled photons, as the low phase space density of neutrons produced by reactors precluded their use in such experiments. In all his career, from TU Vienna through Innsbruck and back to the University of Vienna, Zeilinger has had a most salubrious effect on the work of his colleagues and competitors alike, always noting connections and extensions to be investigated and unstintingly sharing remarks that have enhanced the field of quantum mechanics from foundational to purely applied work.

• Micius Quantum Prize, Micius Quantum Foundation (2019, with Stephen Wiesner, Charles H. Bennett, Gilles Brassard, Artur Ekert and Pan Jianwei)
• Cozzarelli Prize, PNAS and National Academy of Sciences (2019, 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)
• Medal of the Senate of the Czech Republic (2017)
• Willis E. Lamb Award, Physics of Quantum Electronics (PQE) conference (2016, with Stephen E. Harris, Maciej Lewenstein and John Madey)
• TWAS Prize, World Academy of Sciences (2015)
• Academy Medal of the Heidelberg Academy of Sciences and Humanities (2015)
• Medaille du Collège de France (2015)
• Medal of the National Academy of Sciences of Belarus (2014)
• Urania Medal, Urania Berlin (2013)
• Finalist, World Technology Award for Communications Technology, World Technology Network (2012)
• Ben Gurion Medal, Ben-Gurion University of the Negev(2010)
• Wolf Prize in Physics, Wolf Foundation (2010, with Alain Aspect and John Clauser)
• Grand Merit Cross with Star of the Order of Merit of the Federal Republic of Germany (2009)
• ERC Advanced Grant, European Research Council (2008)
• Quantum Communication Award, Tamagawa University (2008)
• Inaugural Isaac Newton Medal, Institute of Physics (2008)
• Quantum Electronics Prize, European Physical Society (2007)
• King Faisal International Prize, King Faisal Foundation (2005)
• Descartes Prize, European Union (2005)
• Lorenz-Oken-Medal, Society of German Scientists and Physicians (2004)
• Klopsteg Memorial Award, American Association of Physics Teachers(2004)
• Sartorius Prize, Sartorius AG(2003)
• Order Pour le Mérite for Arts and Sciences (2001)
• Senior Humboldt Fellow Prize, Alexander von Humboldt Foundation (2000)
• European Optics Prize, European Optical Society (1997)
• European Lecturer (1996)
• Prix Vinci d'Excellence (1995)

• Grand Decoration of Honour in Gold for Services to Vienna, City of Vienna (2018)
• Grand Decoration of Honour for Services to the Republic of Austria (2015)
• Tiroler Adler Orden, State Government of Tyrol (2013)
• Grand Gold Decoration, City of Vienna (2006)
• Wilhelm Exner Medal, Austrian Trade Association (2005).[41]
• Johannes Kepler-Prize, State Government of Upper Austria (2002)
• Austrian Decoration for Science and Art, Republic of Austria (2001, Austrian equivalent to the Order of Merit)[42]
• Visionary of the Year in Science (2001)
• Science Award of the City of Vienna (2000)
• Kardinal Innitzer Würdigungspreis, Roman Catholic Archdiocese of Vienna (1997)
• Austrian Scientist of the Year (1996)
• Junior Prize of the Theodor Körner Foundation (1980)
• Prize for Junior Scientists, Kardinal Innitzer Foundation (1979)
• Prize of the City of Vienna for the Encouragement of Young Scientists (1975)

• Honorary doctorates from the Humboldt University of Berlin (2005), the University of Gdańsk (2006), the National Academy of Sciences of Ukraine (2015), Technion (2020), the Okinawa Institute of Science and Technology Graduate University (2020, award ceremony delayed due to COVID restrictions) and the Israel Institute of Technology (2020, award ceremony delayed due to COVID restrictions)
• Honorary professorships from the University of Science and Technology of China (1996), Nanjing University (2016) and Xi’an Jiaotong University (2019)
• Member of the German Academy of Sciences Leopoldina, Berlin-Brandenburg, Austrian, Slovak Academies of Sciences, the National Academy of Sciences of Belarus, the Academia Scientiarum et Artium Europaea, the Serbian Academy of Sciences and Arts, the Academia Europaea and the French Académie des Sciences
• Foreign Honorary Member of the Romanian Academy of Sciences
• Foreign Member of the Chinese Academy of Sciences (CAS)
• Foreign Member of the Russian Academy of Sciences
• Foreign Member of the U.S. National Academy of Sciences
• Fellow of the American Physical Society, the American Association for the Advancement of Science (AAAS), the World Academy of Sciences (TWAS) and the Optical Society of America (OSA)
• Foreign Associate of the National Academy of Sciences of Belarus
• Socio Corrispondente Straniero, Accademia Galileiana
• Asteroid 48681 Zeilinger named for him to mark his 60th birthday (2005)
• In 2005, Anton Zeilinger was among the "10 people who could change the world", elected by the British newspaper New Statesman.[43][44]

• S.N. Bose Memorial Lecture, S.N. Bose National Centre for Basic Sciences, India (2021)[45]
• David M. Lee Historical Lecture in Physics, Harvard University, USA (2019)[46]
• Bethe Lectures, Cornell University, USA (2016)
• Zhongshan Lecture, Nanjing University, China (2016)
• Robert Hofstadter Memorial Lecture, Stanford University, USA (2015)[47]
• Montroll Memorial Lecture, University of Rochester, USA (2014)
• Herzberg Memorial Lecture, Canadian Association of Physicists, Canada (2012)
• Racah Lectures in Physics, Hebrew University, Israel (2012)
• Cherwell-Simon Memorial Lectures, Oxford University, UK (2012)
• Festkolloquium, 500. WE-Heraeus Seminar, Heraeus-Stiftung, Bad Honnef, Germany (2012)
• Vice-Chancellor's Open Lecture Series, University of Cape Town, South Africa (2011)[48]
• Mark W. Zemansky Lecture, City College of New York, US[49] (2011)
• Van Vleck Lecture, University of Minnesota, US (2011)
• Ockham Lecture, Merton College, Oxford University, UK (2010)[50]
• Dvorak Memorial Lecture, University of Prague, Czech Republic (2010)
• Celsius Lecture, Uppsala University, Sweden (2010)[51]
• Carl Friedrich von Weizsäcker Lectures, University of Hamburg, Germany (2009)
• Festvortrag, 150th birthday of Max Planck, Max Planck Society, German Physical Society, Berlin-Brandenburg Academy of Sciences, Humboldt University Berlin, Germany (2009)
• Inaugural Kavli Colloquium, Kavli Institute of Nanoscience, Delft University of Technology, Netherlands (2009)[52]
• Newton Prize Lecture, Institute of Physics, UK (2008)[53]
• Asher Perez Memorial Lecture, Technion, Israel (2008)
• Wolfgang-Paul Lecture, Bonn University, Germany (2007)[54]
• Seventh Johannes Gutenberg Endowed Professorship, Johannes Gutenberg University Mainz, Germany (2006)[55]
• Colloquium Ehrenfestii, Leiden University, Netherlands (2004)[56]
• Angstrom Lecture, Uppsala University, Sweden (2003)
• Amos de-Shalit Memorial Lecture, Weizmann Institute, Israel (2003)
• Solly Cohen and Shimon Ofer Memorial Lecture, Racah Institute of Physics, Hebrew University of Jerusalem, Israel (2003)
• Schrödinger Lecture, Imperial College, UK (2003)[57]
• Niels Bohr Lecture, Copenhagen University, Denmark (2003)
• Schrödinger Lecture, Trinity College, Ireland (1999)[58]
• H.L. Welsh Lecture in Physics, University of Toronto, Canada (1997)[59]
• Colloquium Ehrenfestii, Leiden University, Netherlands (1996)[56]