Quantum Quantum In physics, a quantum (plural: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a physical property may be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum. For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation). Similarly, the energy of an electron bound within an atom is quantized and can exist only in certain discrete values. (Indeed,
European Physical Journal D European Physical Journal D The European Physical Journal D: Atomic, Molecular, Optical and Plasma Physics is an academic journal recognized by the European Physical Society, presenting new and original research results. The main areas covered are: The range of topics covered in these areas is extensive, from Molecular Interaction and Reactivity to Spectroscopy and Thermodynamics of Clusters, from Atomic Optics to Bose-Einstein Condensation to Femtochemistry. The EPJ D arose from various predecessors: "Il Nuovo Cimento (Section D)", "Journal de Physique", and "Zeitschrift für Physik D". Prior to 1998, this journal was named "Zeitschrift für Physik D: Atoms, Molecules and Clusters".