Ignacio Cirac, a Spanish physicist, and Peter Zoller, an Austrian physicist, both at the University of Innsbruck, published on May 15, 1995, 'Quantum Computations with Cold Trapped Ions', the first concrete, physically realistic model of how to build a universal quantum computer. Until then, quantum computing was above all an abstract concept: Richard Feynman had proposed in 1982 simulating physics with quantum computers, and Peter Shor had developed in 1994 an algorithm capable of factoring large numbers exponentially faster than any classical computer, but no one had proposed a concrete physical system on which to implement the logic gates needed for such a machine. Cirac and Zoller solve the problem by proposing to confine a set of ions — electrically charged atoms — in a linear trap, cool them to extremely low temperatures, and manipulate them with laser beams. Each ion encodes a quantum bit (qubit) in its internal electronic states, while the collective vibrational motion of all the ions in the trap — the 'phonons' — acts as a quantum bus allowing any two ions to be coupled and quantum logic gates executed between them, with essentially negligible decoherence (loss of quantum information). The proposal is so concrete and physically plausible that, just months after its publication, David Wineland's group at NIST achieves the first experimental demonstration of a fundamental quantum logic gate following precisely this scheme. The idea triggers a worldwide experimental race: numerous research groups adopt the trapped-ion scheme as one of the most advanced platforms for building real quantum computers, a position it still holds three decades later. In later work, Cirac and Zoller also propose the use of ultracold atoms in optical lattices as a versatile toolbox for simulating many-body quantum systems — another research line that has given rise to an entire field of quantum simulators.