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I have been looking at several circuits being generated by Stim in the literature, e.g. in https://arxiv.org/pdf/2302.02192.pdf, and I have stumbled upon the operation

circuit.append_operation("SHIFT_COORDS", [], [0,0,1])

Can someone explain how this operation works and what is the effect on the circuit? What coordinates are shifted? Also, why is it only placed after detectors?

Thank you very much in advance!

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SHIFT_COORDS exists so that detectors declared in a REPEAT block can end up with different coordinates from iteration to iteration. Otherwise, when you made a detector error model diagram (or some other thing that uses the coordinates instead of ignoring them), they'd all end up on top of each other.

What SHIFT_COORDS does is to accumulate an offset to add to later coordinate data in DETECTOR and QUBIT_COORDS commands.

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  • $\begingroup$ Thank you very much for your response! May I also ask, what do each of the list arguments following SHIFT_COORDS mean? $\endgroup$ Jan 23 at 5:50
  • $\begingroup$ @EzequielRodriguezChiacchio Well there's the first coordinate shift, the second coordinate shift, the third coordinate shift, etc $\endgroup$ Jan 23 at 9:33

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