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Warning about computation using light. The DeBroglie wavelength of practical light is huge! Don’t expect miniaturization.

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There are still some use cases where light-based computation could work very well without miniaturization, just don't expect it to replace general-purpose chips.

One possible application is in the amplification stages of optical communication links. If you could do error correction in pure optical circuits, you could avoid the optical -> electrical -> optical conversion, and save lots of energy -- something quite relevant for submarine cables, for example.

Good point.

What does this mean?

Light has a wavelength hundreds of nanometers. That means it's hard, if not impossible, to do useful stuff with it with higher density than that. And there is light with shorter wavelengths, like extreme ultraviolet, but it has other disadvantages.

I think it means that quantum effects become a problem when you get to around that size.

No. Actually it’s the extreme difficulty of making coherent light at short wavelengths and, if you succeed, material absorption. If you could overcome these, the quantum effects “help” you, because you have succeeded in making and guiding light at a smaller wavelength, hence miniaturization, which is everything.

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