# Information causality

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Information causality is a physical principle suggested in 2009. Information Causality states that information gain that a receiver (Bob) can reach about previously unknown to him data of a sender (Alice), by using all his local resources and ${\displaystyle n}$ classical bits communicated by the sender, is at most ${\displaystyle n}$ bits.

The principle assumes classical communication: if quantum bits were allowed to be transmitted the information gain could be higher as demonstrated in the quantum superdense coding protocol. The principle is respected by all correlations accessible with quantum physics while it excludes all no-signaling correlations which violate the quantum Tsirelson bound.