Das margens para o centro

A história da segunda revolução quânca

Olival Freire Jr. Universidade Federal da Bahia, Brazil

Ciência às 19 horas Instuto de Física de São Carlos – USP São Carlos 29 Novembro 2016 Alain Aspect, sico francês: duas revoluções quâncas no século XX. • A primeira, na primeira metade do século, deu origem à teoria cienfica que descreve o comportamento dos átomos, a radiação e suas interações. A segunda ocorreu na segunda metade e ainda vem evoluindo, uma vez que ela traz a promessa de computadores quâncos, o que ainda não se concrezou. • O seminário trata das origens desta segunda revolução e apresenta um histórico dos aspectos intelectuais e contextuais resultantes da renovação da pesquisa sobre os fundamentos da sica quânca. O foco será na história do teorema de Bell e do emaranhamento quânco

The vexing conceptual issues:

• Can quantum mechanics be supplemented with addional variables and sll preserve quantum predicons?

– The analogy with stascal mechanics and classical mechanics – Von Neumann’s 1932 proof against hidden variables – Einstein and Bohr debate, 1935. … – Bell’s theorem, 1965: Bell’s theorem Quantum mechanics may violate Bell’s Realism (systems have all inequalies

properes well defined http://upload.wikimedia.org/wikipedia/commons/7/77/Straigh... independent of observaon) + 1.00 Locality (measurement on A does not change B’s state) 0.00 ê 0 90 180 270 360 Quantum Correlation Quantum

Bell’s inequalies -1.00 Angle between detectors (degrees)

−2 ≤ Em(a,b ) + Em(a,b’) + Em(a’,b ) − Em(a’,b’) ≤ 2

1 of 1 11/13/12 9:58 AM Quantum teleportaon between the The long and impressive list Canary Islands La Palma and of experiments: Tenerife over both quantum and classical 143-km free-space channels

Clauser, Holt, 1972 Clauser, Fry, 1976 … Aspect, 1981 and 1982 … New source of entangled photons:

Shih (1988), Mandel, Zeilinger, Gisin …

Entanglement as physical phenomenon X-S Ma et al. Nature (2012) doi:10.1038/nature11472 A Cosmic Bell Test with Measurement Sengs from Astronomical Sources

Johannes Handsteiner, Andrew S. Friedman, Dominik Rauch, Jason Gallicchio, Bo Liu, Hannes Hosp, Johannes Kofler, David Bricher, Mahias Fink, Calvin Leung, Anthony Mark, Hien T. Nguyen, Isabella Sanders, Fabian Steinlechner, Rupert Ursin, Sören Wengerowsky, Alan H. Guth, David I. Kaiser, Thomas Scheidl, Anton Zeilinger hps://arxiv.org/abs/1611.06985, Submied on 21 Nov 2016

In previous experiments, this "freedom of choice" was addressed by ensuring that selecon of measurement sengs via convenonal "quantum random number generators" (QRNGs) was space-like separated from the entangled parcle creaon. […] Here we report on a new experimental test of Bell's inequality that, for the first me, uses distant astronomical sources as "cosmic seng generators." These foundaonal issues could have lain dormant for a long me if not for the role played by the quantum dissidents. See analogies with other controversies in physics

David Bohm, Jean-Pierre Vigier, […], Abner Shimony, John Bell, John Clauser, Bernard d’Espagnat, Franco Selleri, Alain Aspect, Nicolas Gisin, …

They took issue with the prevailing wisdom: They considered there was good physics to be done on these subjects and these issues had not yet been solved by the founding fathers of quantum mechanics

Some of them paid a high professional price due to the exisng bias against the research on these subjects. The sgma against hidden variables in quantum mechanics

• On December 2, 1966, when John Bell had just published his theorem, which contrasted quantum mechanics and hidden variables, Léon Rosenfeld wrote to him: “I need not tell you that I regard your hunng hidden parameters as a waste of your talent; I don’t know, either, whether you should be glad or sorry for that” “When I saw d’Espagnat The most conspicuous case is last week he had a leer John Clauser, the outstanding from the Dep’t Chairman American physicist who never at San Jose, inquiring got a permanent job in the whether what you have been doing is real American academia. physics. Needless to say, he’ll write a strong leer answering the queson in your favor. I’m sorry,

from that evidence, to find that your job situaon is sll unseled.”

Shimony to Clauser, Aug 1972

A milder statement …

• The controversy [on hidden variables] has finally reached a point where it can no longer be decided by any further experimental observaons; it henceforth belongs to the philosophy of science, rather than to the domain of physical science proper. Messiah, Quantum Mechanics, 1961 The Prize Commiee for Physics has unanimously decided that the 2010 Wolf Prize be jointly awarded to:

John F. Clauser; Alain Aspect; and Anton Zeilinger

For their fundamental conceptual and experimental contribuons to the foundaons of quantum physics, specifically an increasingly sophiscated series of tests of Bell’s inequalies or extensions there of using entangled quantum states

Philosophical concerns:

Determinism and realism Varenna 1970 1st summer school on foundaons of quantum mechanics The Woodstock of the quantum dissidents • I graduated with an original thesis on gauge theories, but at that me nobody cared about it. Then, in the polical context of late sixes, we hoped for a deep change not only in society, but even in the way of doing physics. So, we started from the foundaons of Q.M. […] (T. Tone)

• I was among the young physicists who parcipated in the Meeng and Assembly of the Italian Physical Society, in which we cricized instuonal research, and expressly proposed this School in the programs of the Varenna Summer Schools, with the proposal of introducing a reflecon on the foundaons of Physics (A. Baracca) • I found myself in a way, as we say, between the hammer and anvil, between the two, because on one part I had my professors, my old teachers who were not fascists, not at all, but certainly reaconary, and the young people who were pro-Communists, but too much. I said no, you are right here and you are wrong here, and I found myself in a very different posion. But later it was acknowledged that by taking that standpoint, I saved the Italian Physical Society. (Toraldo di Francia)

• I suppose there was, coming from the grassroots, some demands on calling into queson the received views. It was 1970, that is, a me with much polical and intellectual agitaon. In Italy, like in France, there were young physicists who were acvists. This might have played a role (B. d’Espagnat) B. Vitale, The War Physicists [Documents About the European Protest Against the Physicists Working for the American Military […], 1976 On the Other Side of the Atlanc

• The Vietnam War dominated the polical thoughts of my generaon. Being a young student living in this era of revoluonary thinking, I naturally wanted to ‘shake the world.’ Since I already believed that hidden variables may indeed exist, I figured that this was obviously the crucial experiment for finally revealing their existence. The no-cloning theorem, nowadays a central piece in quantum informaon, John Clauser resulted from insgaons from physicists gathered at Berkeley who idenfied themselves with the counter culture In 1970, Physics Today and American Journal of Physics opened a debate on the interpretaons of quantum mechanics

“The very interesng contribuons to the quantum mechanics debate in your April issue, and the paper by DeWi which triggered them, exemplify the highly complex and subtle ways in which scienfic opinion can change. When I was an undergraduate reading physics 20 years ago, [. . . ] the Copenhagen line was “scienfic,” anything else was meaningless, mumbo-jumbo, or, at best, mistaken. Now the curious thing is that, as far as I am aware, there has been no major finding or theorecal insight that could be held to demolish or supersede this interpretaon. Nevertheless, there is now considerable dissasfacon with it, and a willingness to regard other points of view—for example, hidden variables—as being at least respectable.”

M. Hammerton, Leer to Physics Today, 1971 Combinaon of contextual and internal factors:

Bell’s theorem and the series of increasing accurate measurements

The cultural and polical context of the late 1960s

The technical improvements in the 1980s – manipulaon of single quantum systems.

In the early 1990s, the merging of quantum physics with computer science leading to quantum cryptography and quantum informaon Entanglement and decoherence as the physics core of quantum informaon

The ruse of history

The quantum dissidents were victorious, foundaons became a respectable theme.

However they had higher expectaons. John Bell, the iconic figure among the quantum dissidents, used to say that quantum mechanics is “roen,” Hamlet’s famous line, in an oblique reference to Niels Bohr.

The ruse is that in trying to aack the foundaons of quantum mechanics, they ended up consolidang and developing quantum mechanics itself and quantum theory entered the 21st century as vindicated as ever.