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by rdtsc 5481 days ago
Not _info_ transfer but it allows instantaneous collapse of the entangled state into known states after the measurement is done on a entangled system.

Here is how I remember it (and I am just a comp sci nerd, not a physicist so please correct me):

* you have 2 qubits Q1 and Q2. You entangle them. Now you have an entangled system Q1Q2.

* You separate Q1 and Q2 in space. Let's say you put Q2 on a spaceship and blast it into space, but leave Q1 in the lab on earth.

* After some time you measure Q1 to get its value. At that point the entanglement of Q1Q2 collapses. You now know the value of Q1 that you just measured and at the same time Q2 is forced to a known value too.

* At _appears_ as if you could send information this way but you cannot. Think about it. You don't know what value you'll measure in the lab for Q1. So you can't force Q2 to be a certain value either.

* Let's think about it another way -- suppose you tell the spaceship operator that if Q2 collapses to |0> then they should turn the spaceship immediately around and head back home and if it collapses to |1> they should arm their weapons and prepare for an alien attack. Now you are on earth in control of Q1, and you want to force Q2 to be measured to |1> because you know the aliens are coming. There is nothing you can do to Q1 to force Q2 to be measured as |1>.

1 comments

OK, but can you detect in the spaceship when Q2 collapses? (I know no quantum physics beyond a few articles0

If so why can't you simply modulate the signal on top of a series of collapsing entangled pairs. Basically morse code with the timing of the collapses, you don't care what value they collapse too.

Nice try, but no - basically, to use your phrasing, there's nothing to detect when Q2 collapses.
No. You can ask the spaceship to measure Q2 after a certain period of time. So "fly away and at a specific time T measure Q2" would be the command. Sorry I should have made that more clear.