When did quantum mechanics first enable practical technology?

[mjpam]

This thread is primarily the history of quantum mechanics, so I am not sure if it is appropriate for this forum.

I understand that most of the foundational experiments in quantum mechanics were done in the first two or three decades of the 20th century. As far as I can remember, it is hard to explain semiconductor band gap theory without appealing to quantum mechanics, so the development of the solid state transistor required the quantum mechanics to occur.

Is there another technology that applies quantum mechanics that was developed earlier than the transistor?

 

[Bill_K]

X-ray machines

 

[mjpam]

X-ray machines

X-rays were discover before the formalization of quantum mechanics, though.

 

[Ynaught?]

I'd say the transistor.

 

[akhmeteli]

Is there another technology that applies quantum mechanics that was developed earlier than the transistor?

I would say quantum mechanics was applied earlier than that to electronic microscopy, as quantum effects determine the ultimate resolution of this imaging technology.

 

[gomunkul51]

I would say atomic fission was harnessed solely by the use of the quantum theory of physics (Nuclear weapons, thermonuclear power).