semiklassical

Semiklassical is a term used in physics to describe approximations that bridge the gap between classical and quantum mechanics. It's not a distinct theory but rather a set of techniques or a perspective applied when quantum effects are present but can be treated as small perturbations or in a limited regime. In a semiklassical approach, some aspects of a system are described by classical physics, while others are treated quantum mechanically.

A common example is the semiclassical approximation in quantum mechanics, often associated with the WKB (Wentzel-Kramers-Brillouin) method. This method allows for approximate solutions to the Schrödinger equation, particularly in situations where the potential energy changes slowly compared to the de Broglie wavelength of the particle. It effectively uses the classical phase-space description of a particle's motion but incorporates quantum mechanical wave properties.

Semiklassical methods are particularly useful for understanding phenomena like tunneling, where particles can pass through potential barriers even if they classically lack the energy to do so, or for calculating energy levels of atoms and molecules. The goal is often to gain insight into quantum behavior using the more intuitive framework of classical mechanics, or to simplify complex quantum calculations. The validity of a semiklassical approximation depends on the specific system and the regime being considered, typically requiring that quantum effects are not overwhelmingly dominant.