Scribd
Upload
658 views2 pages

Tunneling Effect

Quantum tunnelling occurs when a quantum particle transitions through a classically forbidden state, such as passing through a potential energy barrier that it classically could not have enough energy to surmount. On a quantum scale, particles exhibit wave-like behavior and their wavefunctions can extend through barriers, allowing for a probability of detecting the particle on the other side. This effect is generally only seen on the nanoscale where quantum behavior is more pronounced. Tunnelling was first applied to explain alpha decay of radioactive nuclei, as classically nuclei could not emit particles through the strong nuclear force, but quantum mechanically there is a probability of tunnelling through the barrier. Tunnelling is now understood to be a general phenomenon in quantum

Uploaded by

api-3759956
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOC, PDF, TXT or read online on Scribd
658 views2 pages

Tunneling Effect

Quantum tunnelling occurs when a quantum particle transitions through a classically forbidden state, such as passing through a potential energy barrier that it classically could not have enough energy to surmount. On a quantum scale, particles exhibit wave-like behavior and their wavefunctions can extend through barriers, allowing for a probability of detecting the particle on the other side. This effect is generally only seen on the nanoscale where quantum behavior is more pronounced. Tunnelling was first applied to explain alpha decay of radioactive nuclei, as classically nuclei could not emit particles through the strong nuclear force, but quantum mechanically there is a probability of tunnelling through the barrier. Tunnelling is now understood to be a general phenomenon in quantum

Uploaded by

api-3759956
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOC, PDF, TXT or read online on Scribd
You are on page 1/ 2

Tunneling effect

Quantum tunnelling
Quantum tunnelling (or tunneling) is the quantum-mechanical effect of transitioning
through a classically-forbidden energy state. It can be generalized to other types of
classically-forbidden transitions as well.

Consider rolling a ball up a hill. If the ball is not given enough velocity, then it will not
roll over the hill. This scenario makes sense from the standpoint of classical mechanics,
but is an inapplicable restriction in quantum mechanics simply because quantum
mechanical objects do not behave like classical objects such as balls. On a quantum scale,
objects exhibit wavelike behavior. For a quantum particle moving against a potential
energy "hill", the wave function describing the particle can extend to the other side of the
hill. This wave represents the probability of finding the particle in a certain location,
meaning that the particle has the possibility of being detected on the other side of the hill.
This behavior is called tunnelling; it is as if the particle has 'dug' through the potential
hill.

As this is a quantum and non-classical effect, it can generally only be seen in nanoscopic
phenomena — where the wave behavior of particles is more pronounced.

Availability of states is necessary for tunneling to occur. In the above example, the
quantum mechanical ball will not appear inside the hill because there is no available
"space" for it to exist, but it can tunnel to the other side of the hill, where there is free
space. Analogously, a particle can tunnel through the barrier, but unless there are states
available within the barrier, the particle can only tunnel to the other side of the barrier.
The wavefunction describing a particle only expresses the probability of finding the
particle at a location assuming a free state exists.

Contents
• 1 History and consequences
• 2 Semiclassical calculation
• 3 See also
• 4 References

History and consequences


In the early 1900s, radioactive materials were known to have characteristic exponential
decay rates or half lives. At the same time, radiation emissions were known to have
certain characteristic energies. By 1928, George Gamow had solved the theory of the
alpha decay of a nucleus via tunnelling. Classically, the particle is confined to the nucleus
because of the high energy requirement to escape the very strong potential. Under this
system, it takes an enormous amount of energy to pull apart the nucleus. In quantum
mechanics, however, there is a probability the particle can tunnel through the potential
and escape. Gamow solved a model potential for the nucleus and derived a relationship
between the half-life of the particle and the energy of the emission.

Alpha decay via tunnelling was also solved concurrently by Ronald Gurney and Edward
Condon. Shortly thereafter, both groups considered whether particles could also tunnel
into the nucleus.

After attending a seminar by Gamow, Max Born recognized the generality of quantum-
mechanical tunnelling. He realised that tunnelling phenomena was not restricted to
nuclear physics, but was a general result of quantum mechanics that applies to many
different systems. Today the theory of tunnelling is even applied to

You might also like