John Clive Ward, (1 August 1924 – 6 May 2000) was an Anglo-Australian physicist who made significant contributions to quantum field theory, condensed-matter physics, and statistical mechanics. Andrei Sakharov called Ward one of the titans of quantum electrodynamics. Ward introduced the Ward–Takahashi identity. He was one of the authors of the Standard Model of gauge particle interactions: his contributions were published in a series of papers he co-authored with Abdus Salam. He is also credited with being an early advocate of the use of Feynman diagrams. It has been said that physicists have made use of his principles and developments "often without knowing it, and generally without quoting him." The Ising model was another one of his research interests. In 1955, Ward was recruited to work at the Atomic Weapons Research Establishment at Aldermaston. There, he independently derived a version of the Teller–Ulam design, for which he has been called the "father of the British H-bomb".
Early life John Clive Ward was born in East Ham, London, on 1 August 1924. He was the son of Joseph William Ward, a civil servant who worked in Inland Revenue, and his wife Winifred née Palmer, a schoolteacher. He had a sister, Mary Patricia. He attended Chalkwell Elementary School and Westcliff High School for Boys. In 1938 he sat for and won a £100 scholarship to Bishop Stortford College. He took the Higher School Certificate Examination in 1942, receiving distinctions in Mathematics, Physics, Chemistry and Latin, and was offered a postmastership (scholarship) to Merton College, Oxford. Although the Second World War was raging at the time, Ward was not called up by the Army, and was allowed to complete his Bachelor of Arts degree in Engineering Science with first class honours, studying mathematics under J. H. C. Whitehead and E. C. Titchmarsh. He received a bursary from the Harmsworth Trust, and in October 1946, with the war over, secured a position as a graduate assistant to Maurice Pryce, who had recently been appointed a professor of theoretical physics at Oxford.
Scientific contributions Ward's total number of published papers was only about 20, a fact that reflects a strong sense of self-criticism. He was also critical of what he called "PhD factories" and expressed scepticism towards the importance attached to having a large number of citations. He never supervised graduate students. He received some significant awards, including the Guthrie Medal and Dirac Medal of the University of New South Wales in 1981, the Heineman Prize in 1982, and the Hughes Medal in 1983 "for his highly influential and original contributions to quantum field theory, particularly the Ward identity and the Salam–Ward theory of weak interactions". He became a fellow of the Royal Society in 1965. Andrei Sakharov said Ward was one of the "titans" of quantum electrodynamics alongside Freeman Dyson, Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga and Gian Carlo Wick. In this regard, it has been said that physicists have made use of his principles and developments "often without knowing it, and generally without quoting him."
Quantum entanglement In 1947, Ward and Pryce published a paper in Nature, in which they were the first to calculate, and use, probability amplitudes for the polarisation of a pair of quantum entangled photons moving in opposite directions. For polarisations x and y, Ward derived this probability amplitude to be:
| ψ ⟩ = ( | x , y ⟩ − | y , x ⟩ ) {\displaystyle \left|\psi \right\rangle =(\left|x,y\right\rangle -\left|y,x\right\rangle )}
which can be normalised as:
| ψ ⟩ = 1 2 ( | x ⟩ 1 | y ⟩ 2 − | y ⟩ 1 | x ⟩ 2 ) {\displaystyle \left|\psi \right\rangle ={1 \over {\sqrt {2}}}(\left|x\right\rangle _{1}\left|y\right\rangle _{2}-\left|y\right\rangle _{1}\left|x\right\rangle _{2})}
This can be used to derive the correlation of polarisation of the two photons. Their prediction was confirmed experimentally by Chien-Shiung Wu and I. Shaknov in 1950. This was the first experimental confirmation of a pair of entangled photons as applicable to the Einstein–Podolsky–Rosen (EPR) paradox. The result was subsequently explained by Richard Dalitz and Frank Duarte. Apparently following Dirac's doctrine, Ward was never bothered by issues of interpretation in quantum mechanics. With his Harmsworth scholarship expiring, and seeing few prospects at Oxford, Ward responded to a job advertisement from the University of Sydney. He was offered a position, but when he arrived, found that it was for a tutor, and not a lecturer. He therefore served out the year, then returned to Oxford to complete his Doctor of Philosophy (D.Phil.) thesis on "Some Properties of the Elementary Particles". Ward expected that his thesis, an elaboration of his 1947 paper, would be easily approved by the external examiner, Nicholas Kemmer, but at the last minute Kemmer's place was taken by Rudolf Peierls, who refused to accept it. Only after a forceful argument by the internal examiner, J. de Witt, was the thesis awarded.
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