Fix decomposition of C3SXGate #7230
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The phases used in the decomposition were inverted, so that the gate was actually equivalent to `SdgXGate().control(3)` rather than the intended `SXGate().control(3)`. Note that both gates are valid square roots of `C3XGate()`, which is likely how this went undetected, but the names and value of `ControlledGate.base_gate` did not match. The decomposition of `C4XGate` had a similar negative-phase error, but the prelude cancelled with the use of the inverse `C3SXGate`, resulting in a correct gate in the end. This commit updates `C4XGate` to work with the new `C3SXGate`.
jakelishman
added
the
Changelog: Bugfix
Pull Request Test Coverage Report for Build 1439617041
💛 - Coveralls |
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Should we add a test for this? E.g. with 🙂 Otherwise LGTM 👍🏻 |
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Whoops, not sure why I didn't write those before, thanks. Done in 1afc46a. |
Cryoris
approved these changes
Nov 9, 2021
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Summary
The phases used in the decomposition were inverted, so that the gate was
actually equivalent to
SdgXGate().control(3)rather than the intendedSXGate().control(3). Note that both gates are valid square roots ofC3XGate(), which is likely how this went undetected, but the names andvalue of
ControlledGate.base_gatedid not match.The decomposition of
C4XGatehad a similar negative-phase error, butthe prelude cancelled with the use of the inverse
C3SXGate, resultingin a correct gate in the end. This commit updates
C4XGateto workwith the new
C3SXGate.Details and comments
Fix #7209.