Why people believe this
Two entangled qubits seem connected regardless of distance. If measuring one instantly affects the other, it seems natural to use this as a communication channel faster than light.
The correction
Measuring one entangled qubit does collapse the joint state instantly — but the outcome you get is random. You cannot control what result you get, so you cannot encode a message. The other party sees a random result too, with no way to tell whether your qubit was measured or not. This is the no-communication theorem. Entanglement enables quantum teleportation and superdense coding, but both require a classical channel alongside the entanglement — neither exceeds the speed of light.
Try it in the simulator
What to do
Load the Bell state preset and simulate. Notice the state is 50% |00> and 50% |11> — never |01> or |10>. Now add a measurement gate on q0 at step t2 and simulate multiple times. Every run, both qubits agree. But you cannot control which outcome you get — so you cannot send information.
Research notes
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