Quantum theory, which was formulated in the first three decades of the twentieth century, describes a wide array of phenomena at the molecular, atomic and subatomic scales. Among its many technological applications, three have become ubiquitous in daily life: laser barcode scanners, light-emitting diodes (LEDs) and the global positioning system (GPS).
Nevertheless, quantum physics is still not entirely understood, and some of the phenomena concerned appear to fly in the face of common sense or everyday empirical experience, surprising not only the average layperson but also physicists and philosophers of science. Some of the counterintuitive aspects of quantum theory are due to its probabilistic nature. It offers a set of rules for calculating the probabilities of the possible measurement outcomes of physical systems and in general cannot predict the actual result of a single measurement.
One of the challenging ideas presented by quantum physics is non-locality, an aspect of reality manifested when two or more systems are generated or interact in such a way that the quantum states of any system cannot be described independently of the quantum states of the others. Technically speaking, scientists call such systems entangled, since they are strongly correlated even at a distance and their quantum state is not defined by the quantum states of their component parts.
Another challenging idea, which seems to point in the opposite direction, is contextuality, according to which the outcome of measuring a quantum object depends on the context, meaning other compatible measurements performed at the same time.
Non-locality and contextuality were born with quantum theory but followed independent paths for several decades. In 2014, scientists conducted a study involving a particular case in which they showed that only one of them can be observed in a quantum system. This finding became known as monogamy. The authors conjectured that non-locality and contextuality were different facets of the same general behavior observed either in one way or the other.
Now, however, a study by Brazilian and Chinese researchers has shown both theoretically and experimentally that this is not so. An article on the study is published in Physical Review Letters and highlighted as an Editors' Suggestion.
The research was led by Rafael Rabelo, last author of the article and a professor at the State University of Campinas's Gleb Wataghin Institute of Physics (IFGW-UNICAMP) in Brazil.
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