What applications does quantum physics have, specifically?

[mustang19]

It's often said that modern electronics is based on quantum mechanics. As far as a I can tell however, detailed understanding of quantum mechanics isn't needed to, say, design a transistor. Although quantum mechanics sets a lower bound on the size of electronics, this would be obvious empirically anyway, and it seems that nothing beyond standard engineering and relativity actually has applications in most electronics, lasers, etc. In contrast to atomic physics and pharmaceuticals where it has extensive applications.

Thoughts?

 

[blue_leaf77]

this would be obvious empirically anyway, and it seems that nothing beyond standard engineering and relativity actually has applications in most electronics, lasers, etc.

The invention of laser relied heavily on quantum mechanics, without it, there is no way one can design such an scheme where light can be amplified using stimulated emission. See http://journals.aps.org/pr/pdf/10.1103/PhysRev.112.1940
Also consider those various types of electron microscopes.

 

[Vanadium 50]

detailed understanding of quantum mechanics isn't needed to, say, design a transistor.

What, specifically, of https://en.wikipedia.org/wiki/History_of_the_transistor do you disagree with?

 

[jfizzix]

I would say a study of solid state physics (the quantum mechanics of large blocks of atoms) is not essential to build a transistor in the same way that a detailed study of thermodynamics is not necessary to build an internal combustion engine. However, the discoveries that have arisen as a result of findings in such subfields of quantum physics are what make attempted improvements to these devices likely to succeed.

It is possible to discover a whole lot of physics without knowing the underlying math (Michael Faraday was legendary at this), but an understanding of the physics makes future progress so very much easier.

 

[mustang19]

What, specifically, of https://en.wikipedia.org/wiki/History_of_the_transistor do you disagree with?

It seems to me that it was more a matter of Shockley and others having problems with their prototypes and developing new physics in response to this, then proceeding with theory from the start as in, say, masers. But point taken.

As for lasers, although they certainly involve quantum effects, the principles used in their design cover a tiny part of quantum mechanics. Basically, you could design a laser if you lived in 1925 and understood Kramers transition matrix. None of the rigorous QM concepts we use today like the uncertainty principle are applied in lasers as far as I can tell.

 

[blue_leaf77]

It's true that stimulated emission was predicted by Einstein solely from the consideration of thermodynamics. But let me remind you this, one of the "sacred" rules in laser physics is that, two levels medium cannot be used as the gain medium. Only media which are active in three or more levels can yield population inversion leading to lasing. If quantum mechanics were never invented in the first place, how could they end up with the notion of energy levels?

 

[f95toli]

The most "hands-on" application of QM that I have ever come across is the design of AlGaAs/Ga heterostructures (for e.g. laser diodes). The basic process is to design the "sandwich" of materials which results in a potential landscape (with position on the x-axis and electric potential on the y-axis), where the potential depends on the relative amount of aluminium.
Once you have your "landscape" you get the energy levels -and thereby e.g. the frequency of the laser- by solving the Schrödinger equation.
It is very straightforward and you can even get some reasonable answers using analytical methods.

However, to answer the original questions I would argue that almost everything in moderns physics and electronics depends on QM; often this is "hidden" but just about everything in semiconductor- and solid-state physics uses concepts from QM.
The same thing is (obviously) true for modern chemistry.

 

[DennisN]

@mustang19
There are also tunnel diodes.

Another member on the forum posted about this recent research in another thread, which I found fascinating (I post it as a teaser of the possibility of future applications):

Article: https://www.uni-wuerzburg.de/en/sonstiges/meldungen/detail/artikel/die-erste-elektrisch-betriebene-lichtantenne-der-welt/ (University of Würzburg)
Electrically-driven optical antennas (17 August 2015)
Arxiv: http://arxiv.org/ftp/arxiv/papers/1502/1502.04935.pdf
Nature Photonics: http://www.nature.com/nphoton/journal/v9/n9/abs/nphoton.2015.141.html