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An international research team from Germany and France has created structures in which light fields interact with electrons so strongly that the quantum vacuum itself is significantly altered. Using extremely short bursts of light, they interrupted this coupling much faster than the timescale of a vacuum fluctuation and observed an intriguing ringing of the emitted electromagnetic field, indicating the collapse of the vacuum state. Their key achievement could improve our understanding of the nature of nothingness-the vacuum of space itself, paving a way toward photonics exploiting vacuum fluctuations. The results are published in the current issue of Nature Photonics.

"Spooky action at a distance," Einstein's summation of quantum physics, has been a criticism of quantum mechanics since the field emerged. So far, descriptions of entangled particles to explain their apparently faster-than-light responses, and even explanations for the phase shifts induced by an electromagnetic field in regions where it is zero-the "Aharonov-Bohm" effect-have mostly addressed these concerns. However, recent theoretical and experimental demonstrations of a "counterfactual" quantum communication protocol have proved difficult to explain in terms of physical cause and effect. In this kind of quantum communication, observers on either side of a "transmission channel" exchange information without any particle passing between them-spooky indeed.