Entanglement, Nonlocality, Superluminal Signaling and Cloning

TL;DR

This paper critically reviews proposals for faster-than-light communication using quantum nonlocality and cloning, emphasizing the incompatibility of such schemes with quantum theory and clarifying misconceptions about quantum cloning.

Contribution

It provides a comprehensive critique of superluminal signaling proposals, including the first proof of the no-cloning theorem's role in preventing such schemes.

Findings

Cloning nonorthogonal states is impossible due to the No-Cloning Theorem.

Proposals based on hypothetical cloning machines for superluminal signaling are fundamentally flawed.

Recent similar proposals are also invalidated by the same quantum principles.

Abstract

The paper is a Chapter of a book. In it an exhaustive review of the proposals to send faster than light signals resorting to quantum nonlocality and the reduction process is presented, together with a critical analysis and rebuttal of all proposals. The most interesting part of the Chapter is the one in which the problem of quantum cloning is discussed. Actually, a proposal of superluminal signaling based on an hypothetical cloning machine has been presented by N. Herbert. The proposal does not work just because of the assumption that one can clone nonorthogonal states. The fact that such a machine is incompatible with quantum theory (i.e., the so-called No-Cloning Theorem) has been proved, for the first time, by the author of the present chapter in his referee's report to Herbert's paper. In the final part of the paper some recent (different but similarly not correct) proposals are analyzed and the reasons for which they are basically wrong are presented.