I tried putting some ELSE_CORRELATED_ERROR on my custom made surface code circuit and I am getting this error while counting logical errors. What does it mean? And how can I fix it?


1 Answer 1


This is because you have an error that's flipping more than 15 detectors at once. This can either be because your detector declarations are wrong (e.g. all detectors reach back to the start of time, instead of having local sensitivity regions) or because your error model includes very high weight errors.

Assuming it's the high weight error thing, there's a few things you can do:

  • Have a version of the circuit without the high weight errors, used to generate the detector error model to configure the decoder.
  • Just don't decompose. Use decompose_errors=False (the default) instead of decompose_errors=True.
  • Decompose manually. You know which of your detectors are X type and which are Z type, and you can use this knowledge to split apart the D# terms in the dem into X type and Z type groups. For example, include a coordinate in each detector's coordinate data that is 0 for X and 1 for Z, produce the dem, then generate a new dem by iterating over the error mechanisms of the first dem while separating the detector terms of each error based on their coordinates.

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