Hatim Salih, Zheng-Hong Li, M. Al-Amri, M. Suhail Zubairy
It has long been assumed in physics that for information to travel between two parties in empty space, Alice and Bob, "physically real" entities have to travel between them. The recent techniques of interaction-free measurement [1-5](or quantum interrogation) - where the presence of an object is inferred without the object directly interacting with the interrogating light - has put a question mark over this basic assumption. This found recent application in quantum key distribution (QKD)[6-8], E-91 [9], B-92 [10], in the form of counterfactual QKD [11] - albeit with limited efficiency. Here, using the "chained" quantum Zeno effect [12, 13], we take this logic to its natural conclusion, showing how, in the ideal limit, information can be transferred between Alice and Bob without any physical particles whatsoever traveling between them - and without recourse to the quantum mechanical resource of entanglement. A question of interest is whether it is possible to communicate securely and directly without the need of a key. We consequently propose a new, secure protocol for direct "counterfactual" quantum communication, whose security, we emphasize, does not rely on the prior exchange of a secret key.
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http://arxiv.org/abs/1206.2042
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