Alain Aspect

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Alain Aspect
Aspect in 2015, portrait via the Royal Society
Born (1947-06-15) 15 June 1947 (age 74)[ citation needed ]
Agen, France[ citation needed ]
Alma mater École Normale Supérieure de Cachan (E.N.S., 1965)
Known for Bell test experiments
Scientific career
Fields Physicist
Institutions Institut d'Optique
École Polytechnique
Centre national de la recherche scientifique

Alain Aspect (French:  [aspɛ] ( Loudspeaker.svg listen ); born 15 June 1947) is a French physicist noted for his experimental work on quantum entanglement. [2] [3] [4]



Aspect is a graduate of the École Normale Supérieure de Cachan (ENS Cachan). He passed the 'agrégation' in physics in 1969 and received his master's degree from Université d'Orsay. He then did his national service, teaching for three years in Cameroon.

In the early 1980s, while working on his PhD thesis [5] from the academic rank of lecturer, he performed the Bell test experiments that showed that Albert Einstein, Boris Podolsky and Nathan Rosen's reductio ad absurdum of quantum mechanics, namely that it implied 'ghostly action at a distance', did in fact appear to be realised when two particles were separated by an arbitrarily large distance (see EPR paradox). A correlation between their wave functions remained, as they were once part of the same wave-function that was not disturbed before one of the child particles was measured.

Aspect also received an honorary doctorate from Heriot-Watt University in 2008. [6]


Aspect's experiments, following the first experiment of Stuart Freedman and John Clauser in 1972, were considered to provide further support to the thesis that Bell's inequalities are violated in its CHSH version, in particular by closing a form of the locality loophole. However, his results were not completely conclusive since there were loopholes that allowed for alternative explanations that comply with local realism. [7]

After his works on Bell's inequalities, Aspect turned toward studies of laser cooling of neutral atoms and is mostly involved in Bose–Einstein condensates related experiments.

Aspect at the Ecole Polytechnique. 0012-alain-asp preview ecran.jpg
Aspect at the École Polytechnique.

Aspect was deputy director of the French "grande école" SupOptique until 1994. He is a member of the French Academy of Sciences and French Academy of Technologies, and professor at the École Polytechnique.

Aspect in Budapest, 2013 AlainAspectFotoThaler.JPG
Aspect in Budapest, 2013
Aspect on a visit to Tel Aviv University in 2010 Alain Aspect in Tel Aviv University.jpg
Aspect on a visit to Tel Aviv University in 2010

Awards and honors

Aspect was elected a Foreign Member of the Royal Society (ForMemRS) in 2015. [8] His certificate of election reads

For his fundamental experiments in quantum optics and atomic physics. Alain Aspect was the first to exclude subluminal communication between the measurement stations in experimental demonstrations that quantum mechanics invalidates separable hidden-variable theories and the first to demonstrate experimentally the wave–particle duality of single photons. He co-invented the technique of velocity-selective coherent population trapping, was the first to compare the Hanbury Brown-Twiss correlations of fermions and bosons under the same conditions, and the first to demonstrate Anderson localization in an ultra-cold atom system. His experiments illuminate fundamental aspects of the quantum-mechanical behaviour of single photons, photon pairs and atoms. [1]

In 2005 he was awarded the gold medal of the Centre national de la recherche scientifique, where he is Research Director. The 2010 Wolf Prize in physics was awarded to Aspect, Anton Zeilinger and John Clauser. In 2013 Aspect was awarded both the Niels Bohr International Gold Medal and the UNESCO Niels Bohr Medal. In 2013 he was also awarded the Balzan Prize for Quantum Information Processing and Communication.

Asteroid 33163 Alainaspect, discovered by astronomers at Caussols in 1998, was named after him. [9] The official naming citation was published by the Minor Planet Center on 8 November 2019 ( M.P.C. 118220). [10]

Related Research Articles

EPR paradox Early and influential critique leveled against quantum mechanics

The Einstein–Podolsky–Rosen paradox is a thought experiment proposed by physicists Albert Einstein, Boris Podolsky and Nathan Rosen (EPR), with which they argued that the description of physical reality provided by quantum mechanics was incomplete. In a 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?", they argued for the existence of "elements of reality" that were not part of quantum theory, and speculated that it should be possible to construct a theory containing them. Resolutions of the paradox have important implications for the interpretation of quantum mechanics.

Photon Elementary particle or quantum of light

The photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always move at the speed of light in vacuum, 299792458 m/s. The photon belongs to the class of bosons.

Quantum mechanics Branch of physics describing nature on an atomic scale

Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.

Wave–particle duality is the concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave. It expresses the inability of the classical concepts "particle" or "wave" to fully describe the behaviour of quantum-scale objects. As Albert Einstein wrote:

It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.

Bell's theorem proves that quantum physics is incompatible with local hidden-variable theories. It was introduced by physicist John Stewart Bell in a 1964 paper titled "On the Einstein Podolsky Rosen Paradox", referring to a 1935 thought experiment that Albert Einstein, Boris Podolsky and Nathan Rosen used to argue that quantum physics is an "incomplete" theory. By 1935, it was already recognized that the predictions of quantum physics are probabilistic. Einstein, Podolsky and Rosen presented a scenario that, in their view, indicated that quantum particles, like electrons and photons, must carry physical properties or attributes not included in quantum theory, and the uncertainties in quantum theory's predictions were due to ignorance of these properties, later termed "hidden variables". Their scenario involves a pair of widely separated physical objects, prepared in such a way that the quantum state of the pair is entangled.

A timeline of atomic and subatomic physics.

John Stewart Bell Physicist

John Stewart Bell FRS was a physicist from Northern Ireland and the originator of Bell's theorem, an important theorem in quantum physics regarding hidden variable theories.

Quantum indeterminacy is the apparent necessary incompleteness in the description of a physical system, that has become one of the characteristics of the standard description of quantum physics. Prior to quantum physics, it was thought that

In physics, hidden-variable theories are proposals to provide explanations of quantum mechanical phenomena through the introduction of unobservable hypothetical entities. The existence of fundamental indeterminacy for some measurements is assumed as part of the mathematical formulation of quantum mechanics; moreover, bounds for indeterminacy can be expressed in a quantitative form by the Heisenberg uncertainty principle. Most hidden-variable theories are attempts at a deterministic description of quantum mechanics, to avoid quantum indeterminacy, but at the expense of requiring the existence of nonlocal interactions.

In physics, the principle of locality states that an object is directly influenced only by its immediate surroundings. A theory that includes the principle of locality is said to be a "local theory". This is an alternative to the older concept of instantaneous "action at a distance". Locality evolved out of the field theories of classical physics. The concept is that for an action at one point to have an influence at another point, something in the space between those points such as a field must mediate the action. To exert an influence, something, such as a wave or particle, must travel through the space between the two points, carrying the influence.

Quantum optics is a branch of atomic, molecular, and optical physics dealing with how individual quanta of light, known as photons, interact with atoms and molecules. It includes the study of the particle-like properties of photons. Photons have been used to test many of the counter-intuitive predictions of quantum mechanics, such as entanglement and teleportation, and are a useful resource for quantum information processing.

In Bell tests, there may be problems of experimental design or set-up that affect the validity of the experimental findings. These problems are often referred to as "loopholes". See the article on Bell's theorem for the theoretical background to these experimental efforts. The purpose of the experiment is to test whether nature is best described using a local hidden variable theory or by the quantum entanglement theory of quantum mechanics.

A Bell test, also known as Bell inequality test or Bell experiment, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to Albert Einstein's concept of local realism. The experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables to explain the behavior of particles like photons and electrons. To date, all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave.

Anton Zeilinger Austrian quantum physicist

Anton Zeilinger is an Austrian quantum physicist who in 2008 received the Inaugural 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". Zeilinger is professor of physics at the University of Vienna and Senior Scientist at the Institute for Quantum Optics and Quantum Information IQOQI at the Austrian Academy of Sciences. Most of his research concerns the fundamental aspects and applications of quantum entanglement.

Bohr–Einstein debates Series of public disputes between physicists Niels Bohr and Albert Einstein

The Bohr–Einstein debates were a series of public disputes about quantum mechanics between Albert Einstein and Niels Bohr. Their debates are remembered because of their importance to the philosophy of science, since the disagreements and the outcome of Bohr's version of quantum mechanics that became the prevalent view form the root of the modern understanding of physics. Most of Bohr's version of the events held in Solvay in 1927 and other places was first written by Bohr decades later in an article titled, "Discussions with Einstein on Epistemological Problems in Atomic Physics". Based on the article, the philosophical issue of the debate was whether Bohr's Copenhagen Interpretation of quantum mechanics, which centered on his belief of complementarity, was valid in explaining nature. Despite their differences of opinion and the succeeding discoveries that helped solidify quantum mechanics, Bohr and Einstein maintained a mutual admiration that was to last the rest of their lives.

In physics, complementarity is a conceptual aspect of quantum mechanics that Niels Bohr regarded as an essential feature of the theory. The complementarity principle holds that objects have certain pairs of complementary properties which cannot all be observed or measured simultaneously. An example of such a pair is position and momentum. Bohr considered one of the foundational truths of quantum mechanics to be the fact that setting up an experiment to measure one quantity of a pair, for instance the position of an electron, excludes the possibility of measuring the other, yet understanding both experiments is necessary to characterize the object under study. In Bohr's view, the behavior of atomic and subatomic objects cannot be separated from the measuring instruments that create the context in which the measured objects behave. Consequently, there is no "single picture" that unifies the results obtained in these different experimental contexts, and only the "totality of the phenomena" together can provide a completely informative description.

Quantum mechanics is the study of very small things. It explains the behavior of matter and its interactions with energy on the scale of atomic and subatomic particles. By contrast, classical physics explains matter and energy only on a scale familiar to human experience, including the behavior of astronomical bodies such as the Moon. Classical physics is still used in much of modern science and technology. However, towards the end of the 19th century, scientists discovered phenomena in both the large (macro) and the small (micro) worlds that classical physics could not explain. The desire to resolve inconsistencies between observed phenomena and classical theory led to two major revolutions in physics that created a shift in the original scientific paradigm: the theory of relativity and the development of quantum mechanics. This article describes how physicists discovered the limitations of classical physics and developed the main concepts of the quantum theory that replaced it in the early decades of the 20th century. It describes these concepts in roughly the order in which they were first discovered. For a more complete history of the subject, see History of quantum mechanics.

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A hallmark of Albert Einstein's career was his use of visualized thought experiments as a fundamental tool for understanding physical issues and for elucidating his concepts to others. Einstein's thought experiments took diverse forms. In his youth, he mentally chased beams of light. For special relativity, he employed moving trains and flashes of lightning to explain his most penetrating insights. For general relativity, he considered a person falling off a roof, accelerating elevators, blind beetles crawling on curved surfaces and the like. In his debates with Niels Bohr on the nature of reality, he proposed imaginary devices intended to show, at least in concept, how the Heisenberg uncertainty principle might be evaded. In a profound contribution to the literature on quantum mechanics, Einstein considered two particles briefly interacting and then flying apart so that their states are correlated, anticipating the phenomenon known as quantum entanglement.

Aspect's experiment was the first quantum mechanics experiment to demonstrate the violation of Bell's inequalities. Its irrefutable result allowed for further validation of the quantum entanglement and locality principles. It also offered an experimental answer to Albert Einstein, Boris Podolsky and Nathan Rosen's paradox which had been proposed about fifty years earlier.


  1. 1 2 "Certificate of Election: EC/2015/48: Aspect, Alain". London: The Royal Society. Archived from the original on 2015-09-16.
  2. Experimental Realization of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment: A New Violation of Bell's Inequalities, A. Aspect, P. Grangier, and G. Roger, Physical Review Letters, Vol. 49, Iss. 2, pp. 91–94 (1982) doi : 10.1103/PhysRevLett.49.91
  3. Experimental Test of Bell's Inequalities Using Time-Varying Analyzers, A. Aspect, J. Dalibard and G. Roger, Physical Review Letters, Vol. 49, Iss. 25, pp. 1804–1807 (1982) doi : 10.1103/PhysRevLett.49.1804
  4. Aspect, Alain (2007). "Quantum mechanics: To be or not to be local". Nature. 446 (7138): 866–867. Bibcode:2007Natur.446..866A. doi: 10.1038/446866a . ISSN   0028-0836. PMID   17443174. S2CID   4397846.
  5. "CV". Archived from the original on 2012-03-20. Retrieved 2011-03-05.
  6. "Annual Review 2008: Principal's Review". Archived from the original on 2016-04-12. Retrieved 2016-03-29.
  7. Reference missing
  8. "Alain Aspect | Royal Society".
  9. "(33163) Alainaspect". Minor Planet Center. Retrieved 20 November 2019.
  10. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 20 November 2019.