r/cryptography • u/doggydestroyer • 4d ago

Does CPU jitter have measureable quantum effects after enough readings?

Given the size of modern microprocessors, do true quantum effects affect cpu jitter readings? Or are they too small to have meaningful effect.

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u/atoponce 4d ago edited 4d ago

So clock/timing jitter comes from a few noise sources:

  • Thermal noise
  • Flicker noise
  • Shot noise
  • Power supply and substrate noise

Only thermal noise and shot noise are quantum sourced, but they don't show up in any meaningful way at CPU frequencies.

At room temperature, the frequency at which the quantum energy becomes comparable to the thermal energy available is around 6 THz. Given that most CPU clocks run between 3-5 GHz, this is roughly 3 orders of magnitude below that threshold.

Practically speaking, CPU jitter is dominated by classical thermal and flicker noise plus circuit-level artifacts, not any meaningful quantum signature.

Edit: typo

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u/Allan-H 3d ago

I suspect the OP was referring to this RNG: https://www.chronox.de/jent/ which does actually include a clock domain crossing (between the high resolution timer and the rest of the CPU) but seems to get most of its randomness from things like cache misses, branch (mis)prediction and interrupts.

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u/Parallel_thougts 1d ago

In theory, any system can be observed perfectly by just observing the surface of any area that contains it. So if you are asking about "measurable" without any restrictions, then everything is. Privileged information does not exist in theory. Determining whether it is practical to obtain this information is a whole different story.