What is it about?

Radiation consists of photons. But when you send a pulse of radiation, we want to know what the photons look like when they arrive. Do they have a definite frequency? The answer is no -- otherwise there would be no definite arrival time. But we find that, paradoxically, even if you try to have a definite start and stop to the pulse, you gain more information about the photons that are arriving by also examining the vacuum out ahead of the pulse, and also behind it. This sounds like a violation of causality, but we show that it isn't.

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Why is it important?

This work can help in more precisely designing the fastest-rate photon transmission systems, to be used in secure communication.


I (David DiVincenzo) had wondered for a long time about how much you can localize a photon. The calculations we have done here have finally settled this puzzle in my mind, and have made clear to me that there is no problem having a photon with an indefinite frequency, and therefore an indefinite amount of energy.

David DiVincenzo
Forschungszentrum Jülich

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This page is a summary of: The photonic content of a transmission-line pulse, Proceedings of the National Academy of Sciences, January 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2314846121.
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