Alain Aspect (born 1947, Agen, France) is a French physicist best known for decisive experiments on Quantum entanglement and tests of Bell's theorem that demonstrated violations of local realism, work recognized by the 2022 Nobel Prize in Physics shared with John F. Clauser and Anton Zeilinger. According to the Royal Swedish Academy of Sciences, the trio was honored “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.” Nobel Prize; American Physical Society. (nobelprize.org)

Early life and education

Aspect studied at the École normale supérieure de Cachan (now ENS Paris‑Saclay), passed the agrégation in physics in 1969, and later earned graduate degrees at Université d’Orsay (Paris‑Sud). He fulfilled national service by teaching in Cameroon before returning to France for doctoral work. Britannica; ENS Paris‑Saclay; Université Paris‑Saclay. (britannica.com)

Bell tests and entangled photons (1980–1982)

Working at Orsay, Aspect and collaborators engineered a sequence of experiments using photon pairs from a calcium atomic cascade to test Bell inequalities with unprecedented control. In 1981 they reported strong violations of generalized Bell inequalities using two‑channel polarizers, ruling out broad classes of local realistic theories. Phys. Rev. Lett.. In July 1982 they realized an EPR‑Bohm–type test with two‑channel analyzers, again in agreement with quantum mechanics and in conflict with local hidden‑variable models. Phys. Rev. Lett.. In December 1982, with time‑varying analyzers switched on nanosecond timescales while detectors were separated by about 12 meters, they performed a landmark test further closing locality concerns. Phys. Rev. Lett.; a plain‑language overview recounts the 12‑m separation, 10‑ns switching, and measured S ≈ 0.101 ± 0.02 consistent with quantum predictions. Britannica. (journals.aps.org)

Wave–particle duality and delayed‑choice studies

Beyond Bell tests, Aspect’s group produced seminal demonstrations of single‑photon nonclassicality and complementarity. With colleagues, he reported photon antibunching in multi‑atom resonance fluorescence (1986), a hallmark of quantized light. Phys. Rev. Lett.. Later, Aspect co‑authored an experimental realization of Wheeler’s delayed‑choice thought experiment with single photons, using a quantum random number generator to choose the measurement configuration in a relativistically separated manner. PubMed (Science 315, 2007). (journals.aps.org)

Atom optics and cold‑atom research

From the mid‑1980s, Aspect worked with Claude Cohen‑Tannoudji’s group at the Kastler–Brossel Laboratory on laser cooling of atoms, and subsequently established an atomic‑optics group at the Institut d’Optique Graduate School (Laboratoire Charles Fabry). His team explored atom‑wave phenomena and contributed to the foundations underpinning ultra‑cold‑atom physics and Bose–Einstein condensation. CNRS. (cnrs.fr)

Academic posts and affiliations

Aspect has long held appointments at the Institut d’Optique Graduate School and at École polytechnique, where he has served as Augustin Fresnel Chair; he is also research director emeritus at the CNRS. University and academy profiles note additional stints at ENS Cachan and collaborations at Collège de France. Université Paris‑Saclay; CNRS; APS Physics author profile. (universite-paris-saclay.fr)

Honors and academies

Major distinctions include the CNRS Gold Medal (2005), the Wolf Prize in Physics (2010, shared with Clauser and Zeilinger), the Niels Bohr and Albert Einstein Medals (2012–2013), the Balzan Prize for Quantum Information (2013), election as a Foreign Member of the Royal Society in 2015, and the 2022 Nobel Prize in Physics. CNRS; Royal Society; Nobel Prize. On June 26, 2025, he was elected to the Académie française (seat 22). Académie française; École polytechnique. (cnrs.fr)

Publications

Aspect co‑authored the advanced textbook Introduction to Quantum Optics: From the Semi‑classical Approach to Quantized Light, widely used in atomic and optical physics. [Introduction to Quantum Optics](book://Gilbert Grynberg; Alain Aspect; Claude Fabre|Introduction to Quantum Optics: From the Semi-classical Approach to Quantized Light|Cambridge University Press|2010); see also the publisher’s catalog entry. Cambridge University Press. He authored Einstein et les révolutions quantiques (2019), a concise account of the “first” and “second” quantum revolutions. CNRS Éditions. In 2025, he published a reflective volume Si Einstein avait su (If Einstein Had Known). Odile Jacob/Bookshop.org; Le Monde interview. (cambridge.org)

Impact

The Orsay experiments by Aspect and colleagues transformed the Einstein–Bohr debate into precise, loophole‑reducing tests, and helped launch a modern era in which nonlocal correlations are central resources for quantum communication and computation, a perspective emphasized in the 2022 Nobel announcements. Nobel Prize; Institute of Physics. (nobelprize.org)