Quantum communication: making two from one

In the future, quantum physics could become the guarantor of secure information technology. To achieve this, individual particles of light—photons—are used for secure transmission of data. Findings by physicists from ...

Graphene tunnelling junctions: beyond the breaking point

Molecular electronics is a burgeoning field of research that aims to integrate single molecules as active elements in electronic devices. Obtaining a complete picture of the charge transport properties in molecular junctions ...

Quantum tunnelling in water opens the way to improved biosensing

Researchers at the University of Sydney have applied quantum techniques to understanding the electrolysis of water, which is the application of an electric current to H2O to produce the constituent elements hydrogen and oxygen.

Probing quantum phenomena in tiny transistors

Nearly 1,000 times thinner than a human hair, nanowires can only be understood with quantum mechanics. Using quantum models, physicists from Michigan Technological University have figured out what drives the efficiency of ...

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Quantum tunnelling

Wave-mechanical tunnelling (also called quantum-mechanical tunnelling, quantum tunnelling, and the tunnel effect) is an evanescent wave coupling effect that occurs in the context of quantum mechanics because the behaviour of particles is governed by Schrödinger's wave-equation. All wave equations exhibit evanescent wave coupling effects if the conditions are right. Wave coupling effects mathematically equivalent to those called "tunnelling" in quantum mechanics can occur with Maxwell's wave-equation (both with light and with microwaves), and with the common non-dispersive wave-equation often applied (for example) to waves on strings and to acoustics.

For these effects to occur there must be a situation where a thin region of "medium type 2" is sandwiched between two regions of "medium type 1", and the properties of these media have to be such that the wave equation has "traveling-wave" solutions in medium type 1, but "real exponential solutions" (rising and falling) in medium type 2. In optics, medium type 1 might be glass, medium type 2 might be vacuum. In quantum mechanics, in connection with motion of a particle, medium type 1 is a region of space where the particle total energy is greater than its potential energy, medium type 2 is a region of space (known as the "barrier") where the particle total energy is less than its potential energy - for further explanation see the section on "Schrödinger equation - tunnelling basics" below.

If conditions are right, amplitude from a traveling wave, incident on medium type 2 from medium type 1, can "leak through" medium type 2 and emerge as a traveling wave in the second region of medium type 1 on the far side. If the second region of medium type 1 is not present, then the traveling wave incident on medium type 2 is totally reflected, although it does penetrate into medium type 2 to some extent. Depending on the wave equation being used, the leaked amplitude is interpreted physically as traveling energy or as a traveling particle, and, numerically, the ratio of the square of the leaked amplitude to the square of the incident amplitude gives the proportion of incident energy transmitted out the far side, or (in the case of the Schrödinger equation) the probability that the particle "tunnels" through the barrier.

This text uses material from Wikipedia, licensed under CC BY-SA