Engineering the quantum transport of atomic wavefunctions over macroscopic distances

The manipulation of matter waves had an important role in the history of quantum mechanics. The first experimental validation of matter-wave behaviour was the observation of diffraction of matter by crystals(1), followed by interference experiments with electrons, neutrons, atoms and molecules using gratings and Young's double slit(2-5). More recently, matter-wave manipulation has become a building block for quantum devices such as quantum sensors(6) and it has an essential role in a number of proposals for implementing quantum computers(7,8). Here, we demonstrate the coherent control of the spatial extent of an atomic wavefunction by reversibly stretching and shrinking the wavefunction over a distance of more than one millimetre. The quantum-coherent process is fully deterministic, reversible and in quantitative agreement with an analytical model. The simplicity of its experimental implementation could ease applications in the field of quantum transport and quantum processing.