Forward propagate an error in Stim

Question

The method Circuit.explain_detector_error_model_errors() allows one to check which errors result in certain detector flips and logical flips.

Is the reverse process possible? Can I provide Stim with a CircuitErrorLocation and get which detectors and logicals are flipped?

One way to do it is by creating a circuit with only the desired error we want to propagate, and checking the DEM, but I was wondering if there is a more native method available.

Answer 1

That would be a reasonable method to have, but currently it does not exist.

The closest approximation would be to call stim.Circuit.detecting_regions. This will return a dictionary that allows you to solve the problem for yourself more easily, by looking up detector sensitivities at given times and locations. But it requires a TICK to be present in the circuit at the location where you want the error to be.

An error will set off a detector if it anticommutes with the sensitivity region of a detector at that location and time. You may need to massage the returned data structure a bit more to get something truly fast to query.

import stim
circuit = stim.Circuit.generated(
    "surface_code:rotated_memory_x",
    rounds=5,
    distance=4,
)

detecting_regions = circuit.detecting_regions(
    targets=["L0", (2, 4), stim.DemTarget.relative_detector_id(5)],
    ticks=range(5, 15),
)
for target, tick_regions in detecting_regions.items():
    print("target", target)
    for tick, sensitivity in tick_regions.items():
        print("    tick", tick, "=", sensitivity)

target D1
    tick 5 = +____________________X______________________
    tick 6 = +____________________Z______________________
target D5
    tick 5 = +______X____________________________________
    tick 6 = +______Z____________________________________
target D14
    tick 5 = +__________X_X______XXX_____________________
    tick 6 = +__________X_X______XZX_____________________
    tick 7 = +__________X_X______XZX_____________________
    tick 8 = +__________X_X______XXX_____________________
    tick 9 = +__________XXX_____XXX______________________
    tick 10 = +__________XXX_______X______________________
    tick 11 = +__________X_________X______________________
    tick 12 = +____________________X______________________
    tick 13 = +____________________Z______________________
target D29
    tick 7 = +____________________Z______________________
    tick 8 = +____________________X______________________
    tick 9 = +____________________XX_____________________
    tick 10 = +___________________XXX_______X_____________
    tick 11 = +____________X______XXXX______X_____________
    tick 12 = +__________X_X______XXX_____________________
    tick 13 = +__________X_X______XZX_____________________
    tick 14 = +__________X_X______XZX_____________________
target D44
    tick 14 = +____________________Z______________________
target L0
    tick 5 = +_X________X________X________X______________
    tick 6 = +_X________X________X________X______________
    tick 7 = +_X________X________X________X______________
    tick 8 = +_X________X________X________X______________
    tick 9 = +_X________X_______XX________X______________
    tick 10 = +_X________X________X________X______________
    tick 11 = +_X________XX_______X________XX_____________
    tick 12 = +_X________X________X________X______________
    tick 13 = +_X________X________X________X______________
    tick 14 = +_X________X________X________X______________