You may have seen recent stories claiming that China has teleported an object to space. I would like to take a moment to explain what actually happened.
Here is an example that may help explain what they did…
Imagine I put a cat in a box with a radioactive isotope that has a 50% chance of decaying and killing the cat. This is a quantum system. Until I open the box and determine the state of the cat as alive or dead, both outcome states of the system are true. This is called a superposition of states. At the quantum level, the cat is both alive and dead until one of the two states is observed. This example is called Schroedinger’s Cat.
Now, say my name is Wigner, and I have a friend who is helping me do this Schroedinger’s Cat experiment. We set it all up so the cat is going to be in the box for one hour, and then my friend will open the box and measure the state of the cat. But just as we set it up, I go home for the day. My friend waits an hour and opens the box to observe the state of the cat and take it out of superposition. I come back the next day and ask my friend what happened.
During the time I was away, one of two things could be true. My friend may have measured the cat as alive, or dead. My friend was in superposition JUST LIKE THE CAT. Until he tells me what happened, the state of the cat is tied to the state of my friend. OOOR, you might say, the states are entangled. So once I measure the state of my friend, I know the state of the cat.
This is what they did except with the state of a photon.
That’s not even the spooky part.
Typically within the scope of a relativistic universe like ours, nothing can travel faster than light. But that doesn’t necessarily always hold true with quantum states. Specifically, entanglements ignore this rule. The reason they are calling it teleportation is because when states are entangled, and one is measured, the entanglement function collapses instantaneously, not at the speed of light.
So even if two entangled systems are at opposite ends of the universe, collapsing one will collapse the other instantaneously without waiting for the speed of light between them. Teleportation is probably not the best word for this.
Hopefully that desn’t make any sense, because if it did it wouldn’t be quantum mechanics.