In atoms, an electrons location around the nucleus of an atom can be defined by four quantum numbers: the principal quantum number n , the orbital angular momentum quantum number l , the magnetic quantum number m l , and the electron spin quantum number m s. Nodes indicate regions where an electron has zero probability of being found. The loss of a photon is shown for the electronic transition with an energy of hf. Systems interacting with the environment in which they reside generally become entangled with that environment, a phenomenon known as quantum decoherence. Shapes of atomic orbitals. Table It was the central topic in the famous Bohr—Einstein debates , in which the two scientists attempted to clarify these fundamental principles by way of thought experiments. Want to join the conversation? Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.