Quantum entanglement cannot be used as a means of instant communication, even across vast distances. This concept is often referred to as "quantum teleportation," but it is important to understand that it does not involve the transmission of classical information faster than the speed of light.
Quantum entanglement itself does exhibit non-local correlations, as mentioned earlier, where measurements on one entangled particle can instantaneously affect the state of the other, regardless of the distance between them. However, these correlations cannot be used to transmit information faster than the speed of light.
The reason for this limitation is due to the nature of quantum measurements. When a measurement is made on one entangled particle, it only provides a random outcome or a statistical result. To transmit information, you need a series of measurements that can convey a message. However, these individual measurement outcomes cannot be directly controlled or manipulated to carry a desired message.
To extract useful information from an entangled state, additional classical communication is required. This is because to make sense of the measurement outcomes, the parties involved in the communication must share their measurement results through conventional means, such as sending the results using classical signals, which are limited by the speed of light. Thus, the information transmitted through classical means can only travel at or below the speed of light, preserving the locality of cause and effect.
Quantum entanglement is a fascinating phenomenon with various applications in quantum information science, but it does not provide a means for superluminal communication or instant messaging across large distances.