![]() Is it possible (…) to amplify a quantum state, that is, to produce several copies of a quantum system (the polarized photon in the present case) each having the same state as the original? (…) We show here that the linearity of quantum mechanics forbids such replication and that this conclusion holds for all quantum systems. Wootters and Zurek were quick to disperse this idea: Could quantum mechanics facilitate superluminal communication? ![]() It was titled A single quantum cannot be cloned, and addressed this single, simple, yet tantalizing question. ![]() In October 1982, two scientists – William Wootters from the University of Texas and Wojciech Zurek from the California Institute of Technology – wrote a relatively short (fitting on a single sheet of standard scientific two-column paper) letter to the Nature magazine. I wrote that it was obviously wrong, but I expected that it would elicit considerable interest and that finding the error would lead to significant progress in our understanding of physics. I recommended to the editor of Foundations of Physics that this paper be published. Asher Peres, who was one of the reviewers of this submission, recalls in How the No-Cloning Theorem Got its Name that while it was obvious to him that the paper could not possibly be correct, he still recommended for it to be published: The core theoretical prerequisite for superluminal communication that the paper proposed, was the ability to create perfect copies of quantum states, in unlimited quantities. This potentially earth-shattering concept was of course in violation of the special theory of relativity, but nonetheless – or specifically, because of that – still drew a lot of attention. It was focused on what appeared at first to be an improbable idea – faster than light communication. ![]() In 1981, Nick Herbert submitted a paper called FLASH - A superluminal communicator based upon a new kind of measurement to Springer’s Foundations of Physics journal. In today’s part 6, we shall ask ourselves a seemingly innocent question – how to you clone a quantum state, or in other words, how do you copy a qubit? We grappled with its deeply mysterious behavior and tried to understand and project its consequences onto the Q# code. In the last part of this series we looked at the phenomenon of entanglement – one of the core concepts of quantum theory, which has been fundamentally important in the development of quantum information theory. ![]()
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