Tunnelling Through Quantum Tunnelling

Those Two Words

Quantum tunnelling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier that it cannot surmount under the provision of classical mechanics. Imagine this to be somewhat similar to a football that you hit towards a brick wall. Classical physics predicts that the football will not be able to surpass the wall. However, something phenomenal happens under the effects of quantum tunnelling. The ball appears on the other side, without inflicting any sort of damage to the brick wall. This phenomenon is beyond the scope of classical physics. Hence, quantum mechanics are employed, wherein matter is treated as having properties of both, waves and particles.

Owing to the dual nature of matter, quantum mechanics is highly probabilistic. Under quantum mechanics, consider that when a wave strikes against a barrier, only a part of it will get reflected. There is a small probability that some electrons might penetrate the medium and exist on the other side, similar to, but not exactly like what happens with a refracting light ray.

Where Can I See This Phenomenon

Commonly, this type of tunnelling occurs when a subatomic particle hits barriers of thickness of about 1-3nm or lower. It acts as an influence for some very important macroscopic phenomena, including, but not limited to, the following:

  1. Tunnelling is a source of current leakage in very-large-scale integration (VLSI) electronics and results in the substantial power drain and heating effects that plague high-speed and mobile technology; it is considered the lower limit on how small computer chips can be made.
  2. Tunnelling is a fundamental technique used to program the floating gates of flash memory, which is one of the most significant inventions in consumer electronics.
  3. NUCLEAR FUSION: Temperature and pressure in the core of stars are insufficient for nuclei to overcome the Coulomb barrier in order to achieve a thermonuclear fusion. However, the barrier can be penetrated owing to quantum tunnelling. Though the probability is very low, the extreme number of nuclei in a star generates a steady fusion reaction over millions or even billions of years.
  4. TUNNEL DIODE: A diode, used extensively in the electronics realm, is a semiconductor device which conducts electricity in one direction. Tunnel Diodes- manufactured first by Sony- are semiconductor diodes that experience the tunnelling effect.

    They have a heavily doped p–n junction, about 10 nm wide. The heavy doping results in a broken band gap, where conduction band electron states are more or less aligned with valence band hole states. Due to less width of the depletion region and the increased energy of the charge carriers, they penetrate through the potential barrier, instead of climbing over it, hence exhibiting a tunnelling effect.

    Tunnel diodes are usually made from germanium, but can also be made from gallium arsenide and silicon materials. They find common use in oscillators, amplifiers, and in circuits. They are also used as frequency converters and detectors. Their low capacitance allows them to function at microwave frequencies, above the range of ordinary diodes and transistors.

Common Misconceptions

While it is easy to mistake quantum tunnelling for teleportation, care must be maintained that the two distinct phenomena are not treated as the same. While the latter is a theoretical transfer of energy and matter through two physical points on a macroscopic level, the former is a phenomenon wherein a subatomic particle overcomes a potential barrier against the odds and expectations of classical physics.

While tunnelling phenomena might hold key to teleporting cats across space, they can not be considered to be the same phenomenon…yet.

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