The phenomenon you are referring to is called quantum entanglement, where two or more qubits become correlated in such a way that the state of one qubit cannot be described independently of the other qubits. When qubits are entangled, measuring the state of one qubit instantaneously determines the state of the other qubit, regardless of the distance between them.
Entanglement itself does not allow for the transfer of classical information faster than the speed of light, so it does not violate causality. This is because, even though the measurement of one qubit instantaneously affects the state of the other qubit, the information gained from that measurement cannot be used to transmit classical information.
To understand this, we need to consider a concept called "quantum no-cloning theorem." According to this theorem, it is not possible to make an exact copy of an unknown quantum state. When we measure an entangled qubit, we obtain a random outcome, and we cannot control or predict the result. Therefore, we cannot use the measurement outcome to transmit information faster than the speed of light.
The entangled qubits can be used for certain quantum protocols, such as quantum teleportation or quantum key distribution, which have practical applications in quantum communication and cryptography. However, these protocols require additional classical information to be transmitted alongside the entangled qubits in order to retrieve meaningful information at the receiving end.
In summary, while entangled qubits can exhibit instantaneous correlations, they cannot be used to transmit classical information faster than the speed of light, and thus they do not violate the principle of causality.