No, quantum tunneling is not limited to free particles. It is a phenomenon that can occur for both free particles and particles in bound states, such as those within an atomic nucleus or trapped in a potential well.
Quantum tunneling refers to the probabilistic penetration of a particle through a barrier or potential energy barrier that classically it would not have sufficient energy to overcome. According to quantum mechanics, particles are described by wave functions that can extend into regions where their classical energy would not allow them to exist.
In the case of a free particle, quantum tunneling occurs when the particle encounters a potential energy barrier. Despite not having enough energy to surmount the barrier according to classical mechanics, there is a finite probability that the particle will tunnel through the barrier and appear on the other side.
For particles in bound states, such as electrons in an atom or nucleons in a nucleus, quantum tunneling can also occur. In these cases, the particles are subject to a potential energy well or potential energy barriers created by the surrounding environment. Even though the particles are "bound" to these regions, there is still a non-zero probability for them to tunnel through the barriers or escape from the well.
Quantum tunneling is a fundamental aspect of quantum mechanics and has implications in various phenomena, including nuclear decay, scanning tunneling microscopy, and electron transport in quantum devices, among others.