Preface

An interferometer is a device that makes use of the effect of wave interference. Optical interferometers rely on the interference of light waves. Since the middle of the nineteenth century, interferometry has become a key technique in physics, bringing new insight into the nature of light and the laws of nature. The celebrated interferometry experiment conducted by A. Michelson and E. Morley in 1887 is generally considered to have ruled out the theory of aether and indirectly contributed to the founding of special relativity. The development of lasers since the early 1960s has renewed the field of optics and considerably enhanced the power of interferometers by providing a bright, directed, and coherent source of light for interferometry. Today, optical interferometers range among the most sensitive measurement devices, both for fundamental (gravitational wave detection, astrophysics, ...) and technical (inertial sensing for navigation of planes, satellites, ...) applications. Particle-wave duality, stated at the beginning of the twentieth century, enables the construction of interferometers for matter waves. Since the first observations demonstrating the wave nature of massive particles, ground-breaking interferometry experiments with electrons, neutrons, atoms, or molecules have allowed studying quantum phenomena, investigating the properties of matter, testing the fundamental laws of physics, and performing precision measurements [1]. Over the last decades, in particular with the progress of laser cooling and frequency combs, atom interferometers have evolved into devices at the leading edge of precision measurements. Long-lived coherent superpositions of internal atomic states have been used in atomic clocks to measure time with unprecedented accuracy, providing the definition of the second since 1967. Interferometers using quantum superposition of atomic motional states can also measure accelerations and