From Bell’s theorem to secure quantum key distribution. No signaling and quantum key distribution. Secrecy extraction from no-signaling correlations. General properties of nonsignaling theories.

Teleporting an unknown quantum state via dual classical and Einstein–Podolsky–Rosen channels. Quantum cryptography based on Bell’s theorem.

on Computers, Systems and Signal Processing, Bangalore, India 175–179 (IEEE, 1984)Įkert, A. We suggest that information causality-a generalization of the no-signalling condition-might be one of the foundational properties of nature. Information causality may therefore help to distinguish physical theories from non-physical ones. If only one bit is sent by Alice ( m = 1), this is tantamount to Bob’s being able to access the value of any single bit of Alice’s data (but not all of them). However, no-signalling theories with maximally strong correlations would allow Bob access to all the data in any m-bit subset of the whole data set held by Alice. For m = 0, information causality reduces to the standard no-signalling principle. Namely, if Alice communicates m bits to Bob, the total information obtainable by Bob cannot be greater than m. Using all his local resources (which may be correlated with her resources) and allowing classical communication from her, the amount of information that Bob can recover is bounded by the information volume ( m) of the communication. The principle relates to the amount of information that an observer (Bob) can gain about a data set belonging to another observer (Alice), the contents of which are completely unknown to him. Here we introduce the principle of ‘information causality’ and show that it is respected by classical and quantum physics but violated by all no-signalling theories with stronger than (the strongest) quantum correlations. A broad class of theories exist that share such traits and allow even stronger (than quantum) correlations 3. However, these features do not uniquely define quantum physics. Quantum correlations may be stronger than any classical ones 2, but information cannot be transmitted faster than light (no-signalling). For example, it gives only probabilistic predictions (non-determinism) and does not allow copying of unknown states (no-cloning 1). Quantum physics has remarkable distinguishing characteristics.

Causality principle