This book is an introduction to the field of quantum atom optics, the study of atomic many-body matter wave systems. In many ways, the field mirrors the field of quantum optics – the study of light at its fundamental quantum level. In quantum atom optics, many analogous concepts to quantum optics are encountered. The phenomenon of Bose–Einstein condensation (BEC) can be thought of as the atomic counterpart of lasing. Coherent states of light have analogues with spin coherent states for atoms, which can be visualized with Wigner and Q-functions. In this book, we start from the basic concepts of many-body atomic systems, learn methods for controlling the quantum state of atoms, and understand how such atoms can be used to store quantum information and be used for various quantum technological purposes.
Despite the many analogous concepts, there are also many differences of atoms and photons when treated at the quantum level. Most fundamentally, atoms can be bosons or fermions and possess mass, in contrast to photons. While lasing and BECs both have a macroscopic occupation of bosons, the mechanism that forms the BECs is ultimately at thermal equilibrium, whereas lasing is a nonequilibrium process. Coherent states of light do not conserve photon number, whereas generally atom numbers do not change shot to shot. Another stark difference is that atoms tend to possess much stronger interactions, whereas it is generally difficult to make photons interact strongly with each other. This makes the details of many-body atomic systems often quite different, which often leads to rather different approaches conceptually and theoretically.