Author Topic: Superluminal Communication  (Read 3823 times)

Offline Paul

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Superluminal Communication
« on: January 27, 2010, 07:48:47 PM »
I recently observed the fact that superluminal (faster than light) communication is theoretically possible according to the current laws of quantum mechanics.  It is well known that the laws prove that perfect quantum cloning is an impossibility.  At the same time, however, they also allow the possibility of "imperfect" quantum cloning.  In imperfect cloning, the copied quantum state will not be completely random - it will have some non-unit fidelity to the quantum state being cloned.  In other words there will be some rate of error when cloning a quantum state.  If this theory is true, then it would be possible to create a superluminal communication system.

First, let me define the word "qubit".  I use this term loosely to indicate some measurable quantum state that is either true (1) or false (0).  This could, for example, be "electron is/isn't rotating clockwise around axis A".  Or in the "macro entanglement" experiment I recently read about, it might mean "ion is/isn't oscillating".

Consider the following:  Bob has qubit A, and Bill has qubit B.  The qubits are entangled.  Bob wants to send one bit of information to Bill.  To send a 1, he measures his qubit, causing the states of both A and B to collapse.  To send a 0, he does not measure his qubit, and the states of both A and B remain undetermined.  Then, before measuring his qubit, Bill creates an imperfect clone Bc of quibit B, and then he measures both B and Bc.  If the states of A and B were collapsed by Bob, then the states of B and Bc would both be the same, and Bill would read "1".  If the states of A and B were not collapsed by Bob, then Bill will collapse the states of B and Bc seperately by measuring them, and their states may or may not be the same.  If they are not the same, Bill would read "0".  This could be done numerous times to send a bit stream of audio data, and you'd have a superluminal communication system.

Of course, the received data will be full of errors, because imperfect cloning was used.  But what would it sound like?  Would the message be at all discernible amid the chaos?  To find out, I wrote an applet that simulates the exact type of output that you would receive with a system like this, based on the specified rate of error:

You can change the error rate and compare the effect on Morse code, classical music, and the human voice.  You will notice that Morse code really lends itself to this kind of high-error system.  Even at 95% error rate, the signal is still discernible by the human ear!
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