The second Wu quantum entanglement experiment

F. J. Duarte

F.J. Duarte

Yu Shi

In 1950, Wu and her student published a coincidence experiment on entangled photon pairs that were created in electron–positron annihilation. This experiment precisely verified the prediction of quantum electrodynamics. Additionally, it was also the first instance of a precisely controlled quantum entangled state of spatially separated particles, although Wu did not know about this at the time. In 1956, Wu initiated and led the so-called Wu experiment, which discovered parity nonconservation, becoming one of the greatest experiments of the 20th century. As Yang said, Wu’s experiments were well known for their precision and accuracy. Experimental precision and accuracy manifested Wu’s scientific spirit, which we investigate here in some details. This paper is the transcript of the speech the author made at the International Symposium Commemorating the 110th Anniversary of the Birth of Wu, on May 31, 2022. The above abstract is just the original abstract of the speech.

Yu Shi

In this paper, the historical origins of quantum entanglement in particle physics are systematically and thoroughly investigated. 1957, Bohm and Aharonov noted that the Einstein–Podolsky–Rosen correlation had been experimentally realized in the 1949 experiment of Chien-Shiung Wu and Shaknov. This was the first time in history that spatially separated quantum entanglement was explicitly realized in a controlled experiment. Wheeler first proposed such an experiment as a test of quantum electrodynamics, but his calculation was in error; the correct theoretical calculations came from Ward and Price, as well as from Snyder, Pasternack and Hornbostel, and the result was in accordance with Yang’s 1949 selection rule. After the publication of Bell’s inequality in 1964, it was considered whether it could be tested by using the Wu–Shaknov experiment. This gave an impetus to the field, and a new experiment was done by Wu’s group, though it was not successful as a test of Bell inequality violation. In 1957, Tsung-Dao Lee, Reinhard Oehme and Chen Ning Yang established the quantum mechanical description of the kaons and found that the neutral kaon is a two-state system. In 1958, based on an approach similar to Yang’s 1949 selection rule, Goldhaber, Lee and Yang were the first to write down the entangled states of kaon pairs, in which a single kaon can be charged or neutral. This gave, for the first time, quantum entanglement of internal degrees of freedom of high-energy particles other than photons. In 1960, as unpublished work, Lee and Yang discussed the consequences of quantum entanglement of neutral kaon pairs. We also describe several physicists in the past, especially Ward.

F. J. Duarte

F. J. Duarte