Quarks, which are elementary particles and the fundamental building blocks of protons and neutrons, do not exist as free particles within atomic nuclei. Instead, they are bound together by the strong nuclear force to form these composite particles.
The behavior of quarks within protons and neutrons is described by the theory of quantum chromodynamics (QCD), which is a part of the Standard Model of particle physics. In QCD, quarks are constantly exchanging gluons, which are particles responsible for the strong force. This exchange creates a complex interaction known as confinement, which prevents quarks from existing in isolation.
While it is not accurate to say that quarks within nuclei are in a state of superposition, it is worth noting that the properties of protons and neutrons, such as their spin and charge distributions, are influenced by the collective behavior of the constituent quarks. The dynamics of the quarks within the nucleus are described by QCD and can be quite intricate, but they do not exhibit the same kind of superposition behavior as individual particles in quantum mechanics.