On a recent proposal of faster than light quantum communication

TL;DR

The paper critiques a recent proposal claiming faster-than-light quantum communication using a single-particle superposition, demonstrating that wave packet reduction cannot enable superluminal signaling.

Contribution

It provides a critical analysis of a new proposal for FTL communication, reaffirming the impossibility due to wave function collapse constraints.

Findings

The proposed setup does not allow superluminal communication.

Wave packet reduction cannot be exploited for faster-than-light signaling.

The critique confirms the consistency of quantum mechanics with relativity.

Abstract

In a recent paper, A.Y. Shiekh has discussed an experimental set-up which, in his opinion, should make possible faster-than-light communication using the collapse of the quantum wave function. Contrary to the many proposals which have been presented in the past, he does not resort to an entangled state of two systems but he works with a single particle in a superposition of two states - corresponding to its propagation in opposite directions - one of which goes through an appropriate interferometer. The possibility for an observer near the interferometer to introduce or not, at his free will, a phase shifter along one of the paths should allow to change instantaneously the probability of finding the particle in the far-away region corresponding to the other state of the superposition and, correspondingly, to change the intensity of a beam of particles reaching a distant observer. In this paper we show a flaw in the argument: once more, as it has been proved in full generality a long time ago, the process of wave packet reduction cannot be used for superluminal communication.