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Building a trapped ion quantum computer requires optimizing for different things than a cold atomic clock system. However, a lot of money is currently being dumped into rapidly developing this quantum computing platform. In addition, these systems allow for the generation of large-scale entanglement (and eventually error correction), which would allow for potential entanglement based performance enhancements that would scale favorably in performance as these systems matured/got bigger.

This leads to the question of whether these systems could be used as a potential platform for precise clocks. So my question here is:

  1. Could you use a current state of the art trapped ion quantum computer (e.g. IonQ's latest system) as an atomic clock (e.g. via a Ramsey sequence and using no entanglement for enhancements)?
  2. If so, what sort of clock performance (Allan deviation) could one roughly expect to get?
  3. If not, why not? Or rather, if these systems make for terrible clocks, why?
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People do use trapped ions for atomic clocks, I believe. Generally they are optical clocks, where your "oscillator" is a laser, and then you mix it down to microwave frequencies using a frequency comb.

I think the reason you don't see microwave clocks with trapped ions is that ANY noise or drift on the trapping fields would move the states around and affect clock frequency. The best microwave clocks tend to be in atoms that are not trapped at all, but rather in free fall (in an atomic fountain) shielded from all radiation and all DC electric and magnetic fields of any kind. And that is with neutral atoms. I imagine ions are even more sensitive to background fields.

With optical clocks, the levels you're interacting with optically can be different from the levels you're interacting with to achieve trapping, and there's all this stuff about "forbidden transitions." So I'm sure you still have to do a good job of shielding, but you can also interact with levels that are just more immune to noisy background fields, I think. Plus, tiny shifts in energy levels that are separated by optical frequencies represent a much smaller fractional frequency change than the same shifts in levels separated by microwave frequencies.

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