![]() ![]() Subsequently, it became feasible to think of applications of quantum information processing. Since it takes very carefully engineered quantum states to realize and measure these effects, it took another decade to ascertain their experimental determination the violation of Bell’s inequality ruled out local hidden-variables theories. Alternatives, e.g., so-called local hidden-variable theories, were proposed Bell proved, 30 years later, that these were obliged to fulfill his famous inequality. It is mainly the study of the “second-order” effects of quantum theory, firstly recognized by Einstein, Podolsky, and Rosen in their famous EPR gedankenexperiment: quantum systems can exhibit non-local, entangled correlations unknown in the classical world, which Einstein opposed as “spooky action at a distance”, insisting that the quantum theory must be incomplete. (i) Quantum information science is the basis for the whole of QT 2.0. The primary innovative and non-classical ingredients of the new theory were the following: (i) a superposition of states was now possible, which had not been thinkable in the classical framework (ii) the time evolution of quantum systems was no longer deterministic and, therefore, required a probabilistic description (iii) objective properties, e.g., location and speed at the same time, were no longer existent apart from a determining measurement and (iv), most counter-intuitively, particles that are not locally connected could now correspond via their common wave function-the so-called entanglement. Both led to a full-grown quantum theory in the mathematical formulations of the matrix mechanics of Heisenberg, Born, and Jordan, as well as of Schrödinger’s wave mechanics. The revolution started with Planck’s quantum hypothesis to derive the correct black body radiation and Einstein’s explanation of the photoelectric effect. However, since approximately the turn of the 20th century, certain new phenomena that apparently could not be interpreted in the theoretical frame of classical physics shattered this notion and initiated an unexpected revolution. Compared to the USA, China’s contribution to the worldwide publication output is overproportionate, but not in the segment of highly cited papers.Īt the end of the 19th century, there was a prevalent opinion that the building of physics was complete, and nothing new was left to be discovered. The periods can be characterized by the publication of pioneering works, the exploration of research topics, and the maturing of quantum technology, respectively. Three successive time periods are distinguished in the analyses by their short doubling times in relation to the whole Web of Science. We use a publication set of 54,598 papers from Web of Science, published between 19, to investigate the time development of four main subfields of quantum technology in terms of numbers and shares of publications, as well as the occurrence of topics and their relation to the 25 top contributing countries. These experimental achievements enabled physicists, engineers, and computer scientists to utilize long-known quantum features-especially superposition and entanglement of single quantum states-for a whole range of practical applications. The second quantum technological revolution started around 1980 with the control of single quantum particles and their interaction on an individual basis.
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