At the beginning of the twenty-first century, quantum information theory is an exceptionally lively area of scientific research. Quantum computation and quantum cryptography promise powerful and efficient methods way beyond the scope of classical physics for solving practical problems. Quantum teleportation suggests the even more exciting possibility of achievements that would not even be dreamed of classically, and as minds adapt to new ways of thinking we must expect many other examples.

Quantum information theory emerged from a rich brew of scientific ideas that developed particularly in the 1980s and early 1990s. The ideas centred around the idea of quantum entanglement – the fact that, when two quantum particles have once interacted, even after separation their properties will be mutually dependent in a totally non-classical way. Crucially important were the theoretical analysis and experimental testing of the so-called Bell inequalities, the brain-child of John Bell, a physicist from Ireland.

Bell's main work and the initial experiments were performed in the 1960s and 1970s, respectively, and behind him was the famous Bohr–Einstein debate of the 1920s and 1930s. The Bohr–Einstein debate occurred at a critical point in the intellectual history of the twentieth century. By 1926, the ‘new’ quantum theory of Heisenberg and Schrödinger promised to provide the exact theoretical basis for the physics of atoms, but important questions remained about fundamental aspects of the theory.