Processors used to be mechanical, using macroscopic switches and gears. Then they began to use valve switches. Then they used microscopic circuitry that you could only see with a powerful magnifying glass or a microscope. Now, they're using nanoscale transistors and all manner of quantum tricks so the manufacturers can cram more power into a smaller area.
The same can be said of storage media: there was a time when modified televisions and sound waves travelling through mercury were used as volatile storage. Now we have tiny little SRAM chips that can only be viewed with an electron microscope.
Modern integrated circuits are designed taking into account quantum effects, down to the electron. There must have been a starting point for this, when an effect discovered, identified, isolated or explained using quantum mechanics was first used in hardware as a result of this discovery.
At what point were quantum effects first deliberately designed into classical computing hardware (as a result of their aforementioned discovery, identification, isolation or explanation using quantum mechanics) in order to accomplish a specific effect that could not have been predicted using scientific models not involving quantum mechanics, so that the quantum effect occurs in normal use of the hardware?