Researchers in Saudi Arabia and the US say that it should be possible to exchange quantum information – where two people equipped with suitable optical devices can, in principle, send and receive messages – without transferring even a single photon, meaning that the work is based on the notion of interaction-free measurements.
Put forward by Israeli physicists Avshalom Elitzur and Lev Vaidman in 1993, this involves using light to detect the presence of an object without actually bouncing any photons off it. Elitzur and Vaidman argued that the wave–particle duality of light dictates that an object obstructing one of two paths inside an interferometer can destroy the interference pattern in that device, even though no photons actually come into contact with it – a hypothesis subsequently confirmed experimentally. Another team of researchers used the principle last year to create a quantum-mechanically encoded key for the encryption and decryption of secret messages.
In the latest work, a team of scientists from the King Abdulaziz City for Science and Technology (KACST) and Texas A&M University (TAMU) aimed to find out whether it was possible to use interaction-free measurements to communicate actual messages rather than simply keys. To do this they used the "quantum Zeno effect", a phenomenon in which "a watched kettle never boils". In other words, repeated measurements on a quantum system prevent that system from evolving because of a very high probability that when measured it collapses back into its initial state.
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