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We are trying to simulate the erasure channel in stim, but it is a biased erasure - meaning that the replaced qubit doesn't have a depolarizing channel but a biased channel. We saw that there is a function in stim "HERALDED_ERASE" channel, but here the replaced qubit has a depolarizing channel. Can we use it to have another error channel on the replaced qubit?

Also, when we use MWPM to decode, is the weight of the edge (in the matching graph) associated with the erased qubit updated appropriately?

Thank you!

QEC beginner
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2 Answers2

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Since v1.12, you can use the HERALDED_PAULI_CHANNEL_1 instruction to get biased heralded errors.

Note that you will still need to find a decoder that understands the erasures. For example, as of this writing, pymatching will just ignore the heralds and do normal decoding instead of erasure-informed decoding.

Craig Gidney
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The problem with simulating biased erasure is that resetting the qubit to $|0\rangle$ is not a Pauli channel, while resetting the qubit to the maximally mixed state is. So I'm not sure HERALDED_PAULI_CHANNEL_1 will help... Conditional reset just seems to be a tricky one to simulate efficiently.

(I wanted to comment but I don't have enough reputation haha)

Mingyu Kang
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