Irving Shaknov

Irving Shaknov earned a Bronze Star for valor in the Second World War. He was a graduate student of the Columbia University physicist Chien-Shiung Wu.⁠[1][2]

In 1946 John Wheeler proposed that the pair of photons produced when an electron and a positron annihilate could be used to test a prediction of quantum electrodynamics, namely that the two photons are polarized at right angles to each other. Ernst Bleuler and Helmut Bradt at Purdue University had already observed the angular correlation, but their two Geiger counters were too imprecise for a detailed comparison with theory, and in August 1948 R. C. Hanna at the Cavendish Laboratory concluded from similar experiments that the observed asymmetry ratios were systematically smaller than theory predicts.⁠[1][3][4]

The Physics Today article says that Wheeler made the proposal in October 1946, after returning to Princeton UniversityPrinceton UniversityPrinceton University is a private university and Ivy League member in Princeton, New Jersey. Chartered on October 22, 1746 as the College of New Jersey, it moved to Princeton in 1756 and adopted its present name in 1896. Undergraduate education leads to A.B. and B.S.E. degrees and emphasizes small-group discussion, independent research and residential college life. Graduate education spans the humanities, social sciences, natural sciences and engineering. As of October 2026, Christopher L. Eisgruber was president. Its 2026–27 operating budget was $3.407 billion, including $342 million for undergraduate aid.Open the full entry from his work on the Manhattan ProjectManhattan ProjectThe Manhattan Project was the United States program that developed the atomic bomb during the Second World War, managed from 1942 by the Manhattan Engineer District of the Army Corps of Engineers with British and Canadian participation. It built plants and laboratories at Oak Ridge, Tennessee, Hanford, Washington, and Los Alamos, New Mexico, among other sites, carried out the first nuclear test in 1945, and produced the bombs dropped on Hiroshima and Nagasaki, Japan, later that year; after the war its functions passed to the civilian Atomic Energy Commission.Open the full entry, in a paper entitled “Polyelectrons,” as a test of predictions of the quantum electrodynamics that Paul DiracPaul DiracPaul Dirac (1902–1984) was a British physicist and one of the founders of quantum mechanics and quantum electrodynamics. He formulated the relativistic Dirac equation for the electron and predicted antiparticles, was Lucasian Professor of Mathematics at Cambridge from 1932 to 1969, and shared the 1933 Nobel Prize in Physics with Erwin Schrödinger.Open the full entry had developed in the 1930s. He proposed letting each photon undergo Compton scattering by an electron, detecting each scattered photon separately, using coincident detections to show that the two came from the same annihilation, and taking the asymmetry ratio as the quantity to measure; the article dates the proposal to 11 years after the EPR paper, and its authors point out that such spatially extended unbound singlet states are exactly what Albert EinsteinAlbert EinsteinAlbert Einstein (1879–1955) was a German-born physicist who formulated the special theory of relativity in 1905 and the general theory in 1915 and received the 1921 Nobel Prize in Physics for his discovery of the law of the photoelectric effect. From 1933 until his death he was a professor at the Institute for Advanced Study in Princeton, New Jersey, United States.Open the full entry, Podolsky and Rosen (EPR) had put forward in their thought experiment.⁠[1]

In June 1947 Maurice Pryce of Oxford and his doctoral student John Clive Ward published a calculation of the angular correlation of annihilation radiation in Nature; about five months later Hartland Snyder, Simon Pasternack and John Hornbostel of Brookhaven wrote a paper on the same problem, which appeared in the Physical Review in 1948, and the two groups arrived at the same maximum asymmetry ratio, 2.85 at a scattering angle of 82°. The letter of Bleuler and Bradt in the Physical Review in April 1948 gave an asymmetry ratio of 2.1 ± 0.64 at a scattering angle of 90°; Yu Shi’s paper notes that Hanna used more efficient counter arrangements and obtained asymmetry ratios consistently smaller than predicted.⁠[1][3]

In November 1949 Chien-Shiung Wu and Shaknov carried out the measurement in a laboratory below Columbia University’s Pupin Hall. They bombarded copper with accelerated deuterons to produce unstable copper-64 as a positron source, packed it into a capsule 8 millimeters long, and recorded the gamma photons from the annihilation with two detector sets made of photomultiplier tubes and anthracene crystal scintillators.⁠[1][4]

The Scientific American article says that the deuterons came from a cyclotron (the Columbia cyclotron, in Yu Shi’s paper) and repeats the university folklore that the machine’s multiton magnet was so gigantic that, a decade earlier, administrators had to blast a hole in an exterior wall and recruit the football team to maneuver the block of iron into the building. A figure caption in Physics Today specifies that the two photons first underwent Compton scattering in aluminum and were then detected by the flash they produced in the anthracene crystals. Yu Shi’s paper states that the mean scattering angle was very close to 82°, where theory puts the maximum of the asymmetry ratio, and attributes the success of the experiment in part to Chien-Shiung Wu’s work on sensitive gamma-ray detectors for the Manhattan Project; the Scientific American article says that the two collected significantly more data than the earlier teams. The Physics Today article explains that fixing each detector in turn was meant to eliminate potential experimental errors in the angular correlation measurements; the Scientific American article notes that Chien-Shiung Wu was known for the precision of her experimental designs and had confirmed Enrico FermiEnrico FermiEnrico Fermi (1901–1954) was an Italian-American physicist who received the 1938 Nobel Prize in Physics and in 1942 led the team that achieved the first controlled nuclear chain reaction in Chicago.Open the full entry’s theory of beta decay the year before.⁠[4][1][3]

One detector was kept fixed while the other was placed at relative azimuthal angles of 0°, 90°, 180° and 270°; then the second was fixed and the first rotated, the whole measurement running continuously for 30 hours. The scintillation counters were about ten times as efficient as Geiger counters, which raised the coincidence rate about a hundredfold.⁠[1][3]

On January 1, 1950, the two published their results as a one-page letter of fewer than 1,000 words in the Physical Review (volume 77, page 136), signed C. S. Wu and I. Shaknov.⁠[1][4][3]

The letter gives an asymmetry ratio of 2.04 ± 0.08, to be compared with a theoretical value of 2.00; for ideal geometry the theoretical maximum of the asymmetry ratio is 2.85, at a scattering angle of 82°.⁠[1][3]

Yu Shi’s paper describes the publication as a “Letter to the Editor,” and the reference list of CNA’s history places it in volume 77, number 1, of the Physical Review. The Physics Today article speaks of the satisfactory agreement of their result with the theoretical predictions; of the earlier work it says that the margin of error of Bleuler and Bradt left insufficient evidence to validate or refute the theory and that the asymmetry ratios Hanna observed were systematically smaller than theory predicts. CNA’s account says that the paper, published in “the prestigious Physical Review,” described an experiment he had conducted with his professor.⁠[3][5][1][2]

The letter does not mention the argument of Einstein, Podolsky and Rosen or speak of entanglement; it presents the experiment as a test of Wheeler’s prediction.⁠[6][4]

He received a Ph.D. in physics from Columbia University. Soon after completing his dissertation in 1951 he joined the Operations Evaluation Group; in 1962 that group and several other analysis groups were amalgamated into the Center for Naval Analyses, and CNA’s published history lists CNA Corporation as the name from 1990.⁠[2][5]

The Operations Evaluation Group was a contractor organization administered by the Massachusetts Institute of Technology that carried out studies for the United States Navy; the institute was its academic sponsor from 1945 to 1962.⁠[6][5]

CNA’s history lists Columbia University as academic sponsor for 1942–1945 and the Massachusetts Institute of Technology for 1945–1962, and states that the institute held the Navy’s contract for the Operations Evaluation Group’s services. The organization began in 1942 as the Anti-Submarine Warfare Operations Research Group, became the Operations Research Group in 1944 and the Operations Evaluation Group in 1945, and the same box lists the later names Center for Naval Analyses (1962) and CNA Corporation (1990); the history, published in 2021, says that it continues to this day as an important part of CNA’s Center for Naval Analyses. The Physics Today caption calls it a “military service agency” to the United States Navy.⁠[5][1]

In 1952 he went out to join other Operations Evaluation Group analysts supporting United StatesUnited StatesThe United States is a federal country in North America made up of 50 states, the District of Columbia as the seat of government, and territories such as Puerto Rico and Guam; its capital is Washington, D.C. The Continental Congress adopted the Declaration of Independence on July 4, 1776. The 2020 census (April 1, 2020) counted a resident population of 331,449,281, and the 435 seats of the House of Representatives are apportioned among the states on the basis of the census.Open the full entry forces in the Korean War. The civilian scientists’ mathematical models had already disproved the assumption that North Korean troops were largely being resupplied by sea, and his task was to collect and interpret data on the most effective methods of cutting off supply routes on land.⁠[2][5]

His colleagues knew him as “Spike.”⁠[2]

The analysts had found that Marine Corps night fighters flying at extremely low altitude were very effective at hitting supply trucks, but that the squadrons had difficulty finding enough targets. To gather data on the problem, Shaknov flew deep into North Korea on the night of May 14, 1952, in the radar operator’s position of a black two-seat Tigercat fighter. As the aircraft strafed a truck convoy, an antiaircraft shell hit one of its engines, and he was unable to eject before it crashed.⁠[2][5]

The American Battle Monuments Commission’s record describes him as a civilian attached to the Naval Forces Operational Evaluation Group in Korea who was flying that night as radar observer in an F7F-3N Tigercat of Marine Night Fighter Squadron 513 (Marine Air Group 33, 1st Marine Air Wing) on a night armed reconnaissance mission; the aircraft took a direct antiaircraft hit, exploded and crashed, and he was listed as Missing in Action.⁠[7]

CNA’s account says that by the age of 28 he already had the medal, the doctorate and the published paper, “more honors than most men could ever hope for”; the Physics Today article gives his age at death as 30.⁠[2][1]

He was posthumously awarded the Medal of Freedom, which his family accepted. CNA analysts have served in forward deployment in every major conflict involving United States troops since the Second World War, and he remains the only one to have been killed in action.⁠[2][5][6]

CNA’s account, after listing his early honors, says that another honor lay ahead, one that “could never be wished upon such a promising young man,” and goes on to the posthumous Medal of Freedom; the American Institute of Physics’ article describes his story as tragic and says that he was killed in 1952, while flying on a mission in Korea, when his plane was shot down by enemy fire.⁠[2][6]

Columbia University’s Roll of Honor lists him under the Korean War with Columbia College as his school and 1952 as his class year; it describes him as a civilian physicist working for the “Operations Analysis Group,” which it calls “a military service agency,” and dates the shooting down of his plane, during a secret mission over enemy territory, to May 15, 1953, which it also prints as his date of death. The other sources cited in this section give the night of May 14, 1952.⁠[8]

In 1957 David Bohm and Yakir Aharonov, in a paper in volume 108 of the Physical Review, used the data of the Wu–Shaknov experiment to show that the entangled state, not a classical mixture, gives the observed result; Bohm acknowledged Chien-Shiung Wu in a footnote to that article.⁠[3][6][4]

The American Institute of Physics’ article says that it was Bohm who found the 1950 paper and that its data matched a calculation he had asked Aharonov to make. Yu Shi’s paper explains that Furry had proposed in 1935 that separated entangled particles reduce to product states or a classical probabilistic mixture of them, and that Bohm and Aharonov in their 1957 paper still used the word “correlation,” not “entanglement.” The paper adds that Heitler, and Snyder, Pasternack and Hornbostel, had earlier written down the state of the photon pair without recognizing its significance for entanglement.⁠[6][3]

The experiment remained a standard citation as interest in testing the EPR paradox grew during the 1960s and beyond. In 1960 Asher Peres and Paul Singer contended that an analysis of photon behavior, and thus the Wu–Shaknov experiment, could not resolve whether the correlations were preserved, and at the 1962 conference at Xavier University Podolsky and Aharonov both cited its relevance.⁠[6]

The same article says that the 1960 paper of Peres and Singer suggested alternative approaches but made few waves, and that the 1962 conference at Xavier University in Cincinnati was organized by Boris Podolsky. Around 1964 Eyvind Wichmann suggested a photon-polarization correlation experiment to Carl Kocher, who completed it as his thesis in 1967 and discussed the Wu–Shaknov experiment in an appendix; the article that Kocher and Commins published that year connected their work with it in its second paragraph, and Abner Shimony, a philosopher-physicist then working at the Massachusetts Institute of Technology, and John Clauser, then a graduate student at Columbia University, each later took Kocher’s experiment as a starting point.⁠[6]

John Bell published the inequality named after him in 1964. Yu Shi’s paper states that the Wu–Shaknov arrangement could not test it, because it compared only parallel and perpendicular orientations, as Shimony and Clauser pointed out; the Physics Today article says that a visit by Clauser to Columbia University in 1975 renewed Chien-Shiung Wu’s interest in the angular correlation of high-energy gamma photons. Yu Shi’s paper names two further obstacles: scattering by electrons transfers the entanglement too weakly to violate the inequality, and annihilation photons are too energetic to be measured with polaroids.⁠[3][1]

In 1971 Chien-Shiung Wu designed a new version of the 1949 experiment, writing that it “should certainly quiet those proponents of the hidden variables.”⁠[4]

With her graduate students Leonard Kasday and John Ullman she also carried out a new experiment on Compton-scattered photons.⁠[1]

The paper on this experiment appeared in Il Nuovo Cimento B in 1975 (volume 25, starting on page 633); one detector could be set at arbitrary azimuthal angles relative to the other, which was fixed. The three concluded that, if the polarization of the photons could be detected ideally, their results would violate Bell’s inequality; Yu Shi’s paper notes that the conclusion rested on two assumptions, that an ideal polarization analyzer exists and that quantum mechanics correctly describes the analyzers and Compton scattering.⁠[1][3]

Anton Zeilinger wrote in 1999 that “an earlier experiment by Wu and Shaknov (1950) had demonstrated the existence of spatially separated entangled states.”⁠[4]

The American Institute of Physics’ history article notes that recent writers, among them Indianara Silva, Michelle Frank, Chon-Fai Kam and colleagues, and Yu Shi, stress its importance as the first experiment to clearly demonstrate entanglement; it adds that little documentation survives beyond the paper itself and that many of these authors are still looking for evidence that Wu and Shaknov had the EPR thought experiment in mind but chose not to mention it.⁠[6]

The Atomic Heritage Foundation’s profile suggests that the experiment may have been inspired by Chien-Shiung Wu’s understanding of the 1935 paper of Einstein, Podolsky and Rosen. CNA’s account calls it “one of the seminal tests of quantum physics.”⁠[9][2]

The Scientific American article says that historians agree that the Wu–Shaknov experiment was the first to document entangled photons, while noting that it was not designed to rule out competing explanations. It presents the research of the historian Indianara Silva, a professor of physical sciences and history at the State University of Feira de Santana in Brazil, published in The Oxford Handbook of the History of Quantum Interpretation (2022), who traced the publications from Bohm’s 1957 paper to Zeilinger that credit the experiment and holds that it inspired decades of research on the foundations of quantum mechanics. The physicist F. J. Duarte in 2012 described Wheeler’s “pair theory” as the essence of entanglement. David Kaiser observes that in the 1950s and 1960s research on quantum foundations was stigmatized as junk science and that some researchers disguised such work to protect their careers; the article offers as a conjecture that Chien-Shiung Wu may have done so for similar reasons.⁠[4]

The Physics Today article calls the experiment the first conclusive verification of photon entanglement, nearly 15 years after the EPR paper of 1935, and observes that quantum entanglement has in recent decades become the cornerstone of quantum information, quantum computation and quantum technology. Yu Shi’s paper calls it the first experiment to produce quantum entanglement in a controlled manner and Chien-Shiung Wu the experimental pioneer of entanglement; its acknowledgment records that Chen Ning YangChen Ning YangChen Ning Yang (1922–2025) was a theoretical physicist born in Hefei, Anhui, China, who shared the 1957 Nobel Prize in Physics with Tsung-Dao Lee for their investigation of the parity laws. In 1954 he and Robert L. Mills formulated non-Abelian gauge theory (Yang–Mills theory), and he worked in turn at the Institute for Advanced Study, Stony Brook University and Tsinghua University.Open the full entry advised the author to include her work on entanglement. The Atomic Heritage Foundation’s profile places the experiment in the basement of Pupin Hall and says that many believe the experiment was critical to scientists’ fundamental understanding of quantum mechanics, that its significance was not officially recognized during her lifetime, and that this was underscored by the 2022 Nobel PrizeNobel PrizeThe Nobel Prize is an international award established under the will of Alfred Nobel, comprising five prizes in physics, chemistry, physiology or medicine, literature and peace, awarded since 1901; its funds are managed by the Nobel Foundation, whose Board is based in Stockholm. The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, established in 1968, is not a Nobel Prize.Open the full entry for work on entanglement.⁠[1][3][9]

The 2022 Nobel Prize in Physics was shared by John Clauser, Alain Aspect and Anton Zeilinger. The Scientific American article notes that Chien-Shiung Wu was not mentioned when the prize was announced; the Physics Today article points out that she had died in 1997 and that Nobel Prizes are not awarded posthumously.⁠[4][1]

CNA’s headquarters has an Irving Shaknov Conference Center, in which his portrait hangs.⁠[2][5]

In a photograph printed in Physics Today he stands at the left, wearing a cap; the caption is based on a publication of the Center for Naval Analyses. The American Institute of Physics’ article carries a photograph of him in Korea, credited as courtesy of CNA Corporation.⁠[1][6]

CNA: Official website: https://www.cna.org/ (opens in a new window).⁠[10]

Columbia University: Official website: https://www.columbia.edu/ (opens in a new window).⁠[11]