Quantum mechanical tunneling, also known as quantum tunneling or barrier penetration, is a phenomenon in quantum mechanics where a particle can pass through a potential energy barrier even when it does not have enough classical energy to overcome the barrier.
According to classical physics, if a particle encounters a barrier with higher energy than its own, it would be expected to be reflected back or be unable to pass through. However, in quantum mechanics, particles are described by wave functions that can exhibit wave-like properties, including the ability to spread out and penetrate regions of space that are classically forbidden.
When a particle encounters a potential energy barrier, its wave function extends into the barrier region. Through a process called tunneling, there is a finite probability that the particle can "tunnel" through the barrier and emerge on the other side, even if its energy is lower than the barrier's height. This means that a particle can appear on the other side of the barrier even though it does not have enough energy to overcome the barrier classically.
Quantum tunneling is a fundamental aspect of quantum mechanics and has important implications in various areas of physics, including nuclear physics, solid-state physics, and even in devices like tunnel diodes. It is also relevant in understanding phenomena such as alpha decay, where alpha particles can escape from the nucleus of an atom through a classically forbidden region.
The probability of tunneling depends on several factors, including the barrier height and width, the energy of the particle, and the mass of the particle. In general, the lower the energy of the particle and the narrower and higher the barrier, the higher the probability of tunneling.
Quantum tunneling is a remarkable and counterintuitive aspect of quantum mechanics, and its understanding and application have led to significant advancements in various fields of science and technology.