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Fix kraus channels for fallbacks to super-operators#7537

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mhucka merged 5 commits intoquantumlib:mainfromdstrain115:kraus_protocol_fixes

Jul 25, 2025

Merged

Fix kraus channels for fallbacks to super-operators#7537

mhucka merged 5 commits intoquantumlib:mainfromdstrain115:kraus_protocol_fixes

Jul 25, 2025

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dstrain115 commentedJul 25, 2025•
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There were a few issues with the new strategy to fall back to super-operator calculations using apply_channels.
First, the super_operator_to_kraus function is generally not precise or numerically stable enough to support an atol of 1e-10 so loosened this to 1e-6 and also allowed the ability to specify this as a parameter.
Next, some operators define decomposition, so cirq.kraus should try to decompose and get a unitary before falling back to using apply_channel.

Fixes:#7536

Fix kraus channels for fallbacks to super-operators

3c6d299

- There were a few issues with the new strategy to fall backto super-operator calculations using apply_channels.- First, the super_operator_to_kraus function is generally notprecise or numerically stable enough to support an atol of 1e-10so loosened this to 1e-6 and also allowed the ability to specifythis as a parameter.- Next, some operators define decomposition, so cirq.kraus shouldtry to decompose and get a unitary before falling back tousing apply_channel.

dstrain115 requested review froma team andvtomole ascode owners

July 25, 2025 18:05

dstrain115 requested a review fromfdmalone

July 25, 2025 18:05

github-actionsbot added the size: S10< lines changed <50 label

Jul 25, 2025

Fix lint issue.

c352590

mhucka requested changes

Jul 25, 2025

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LGTM with requests for some minor docstring adjustments.

cirq-core/cirq/protocols/kraus_protocol.pyShow resolvedHide resolved

cirq-core/cirq/protocols/kraus_protocol.py Outdated

		default: Determines the fallback behavior when `val` doesn't have
		a channel. If `default` is not set, a TypeError is raised. If
		default is set to a value, that value is returned.
		atol: If calculating kraus channels from channels, use this tolerance

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mhuckaJul 25, 2025

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Typo: kraus → Kraus

cirq-core/cirq/protocols/kraus_protocol_test.py Outdated



		deftest_kraus_channel_with_has_unitary():
		"""CZSWAP is a gate with no unitary but has a unitary."""

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I think there is something wrong with this docstring ;-)

dstrain115 added3 commits

July 25, 2025 11:24

Docstrings

29fafac

Fix moment test.

f1eb5e9

remove unneeded line

2835273

dstrain115 requested a review frommhucka

July 25, 2025 22:17

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codecovbot commentedJul 25, 2025•
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.53%. Comparing base (31df8ef) to head (2835273).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@##             main    #7537      +/-   ##==========================================- Coverage   97.53%   97.53%   -0.01%==========================================  Files        1095     1095                Lines       99006    99014       +8     ==========================================+ Hits        96570    96576       +6- Misses       2436     2438       +2

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Jul 25, 2025

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LGTM

mhucka added this pull request to themerge queue

Jul 25, 2025

Merged via the queue intoquantumlib:main with commit6d10979

Jul 25, 2025

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This was referencedAug 5, 2025

Add a new transformer that performs random pauli insertion#7558

Closed

update the RB fitting method to compensate for the standard deviation induced from the random number generator#7562

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pavoljuhas pushed a commit that referenced this pull request

Aug 14, 2025

Fix kraus channels for fallbacks to super-operators (#7537)

6f1a975

- There were a few issues with the new strategy to fall back tosuper-operator calculations using apply_channels.- First, the super_operator_to_kraus function is generally not preciseor numerically stable enough to support an atol of 1e-10 so loosenedthis to 1e-6 and also allowed the ability to specify this as aparameter.- Next, some operators define decomposition, so cirq.kraus should try todecompose and get a unitary before falling back to using apply_channel.Fixes:#7536