Delayed Phase Correction

[pehamTom]

Description

This PR introduces a feature where stabilizer phases are ignored during Clifford synthesis. If that happens, the phases are corrected during a post-processing step.

Fixes #326

Checklist:

• [ ] The pull request only contains commits that are related to it.
• [ ] I have added appropriate tests and documentation.
• [ ] I have made sure that all CI jobs on GitHub pass.
• [ ] The pull request introduces no new warnings and follows the project's style guidelines.

[burgholzer]

Hey @pehamTom 👋🏼

Haven't looked through this at all yet. Just a brief question: Is this something that's always guaranteed to be faster than the original version? If so, could we just fully replace the old version and avoid adding all those if statements for deciding between both options? Just thinking about maintainability here.

[pehamTom]

Ignoring the phase during synthesis does not guarantee depth-optimality. One could always back-propagate Paulis and fuse them with any single-qubit gates as a post-processing step. But I think it makes sense to respect the chosen gateset and leave the rest up to the user.

I wanted to compress the settings we have anyway. The maxsat method should be removed entirely for example as it is always worse. But that is something for another PR.

[codecov[bot]]

Codecov Report

Merging #397 (4b48b48) into main (5453be3) will increase coverage by 0.1%. Report is 2 commits behind head on main. The diff coverage is 96.2%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #397     +/-   ##
=======================================
+ Coverage   92.3%   92.4%   +0.1%     
=======================================
  Files         44      49      +5     
  Lines       4158    4468    +310     
  Branches     701     764     +63     
=======================================
+ Hits        3839    4132    +293     
- Misses       319     336     +17     

Flag	Coverage Δ
cpp	92.0% <96.2%> (+0.2%)	:arrow_up:
python	95.9% <ø> (ø)

Files	Coverage Δ
include/cliffordsynthesis/Configuration.hpp	100.0% <ø> (ø)
include/cliffordsynthesis/Tableau.hpp	97.6% <100.0%> (+0.5%)	:arrow_up:
...de/cliffordsynthesis/encoding/ObjectiveEncoder.hpp	100.0% <100.0%> (ø)
include/cliffordsynthesis/encoding/SATEncoder.hpp	100.0% <ø> (ø)
...e/cliffordsynthesis/encoding/SingleGateEncoder.hpp	100.0% <ø> (ø)
...lude/cliffordsynthesis/encoding/TableauEncoder.hpp	100.0% <100.0%> (ø)
src/Architecture.cpp	95.0% <100.0%> (ø)
src/cliffordsynthesis/CliffordSynthesizer.cpp	97.5% <100.0%> (+<0.1%)	:arrow_up:
src/cliffordsynthesis/Utils.cpp	100.0% <100.0%> (ø)
...rc/cliffordsynthesis/encoding/MultiGateEncoder.cpp	100.0% <100.0%> (ø)
... and 10 more

... and 1 file with indirect coverage changes

[burgholzer]

Ignoring the phase during synthesis does not guarantee depth-optimality. One could always back-propagate Paulis and fuse them with any single-qubit gates as a post-processing step. But I think it makes sense to respect the chosen gateset and leave the rest up to the user.

I wanted to compress the settings we have anyway. The maxsat method should be removed entirely for example as it is always worse. But that is something for another PR.

Sorry for responding so late here. For some reason, I missed the notification for the message.

I see! In that case, the separate option definitely makes sense. Compressing the settings is definitely much appreciated (in a separate PR, of course).

Is this PR ready for review then?

[pehamTom]

Now it is ready for review.

[github-actions[bot]]

Cpp-Linter Report :warning:

Some files did not pass the configured checks!

clang-tidy reports: 1 concern(s)

• src/Architecture.cpp

  /src/Architecture.cpp:95:21: warning: [readability-identifier-naming]

  invalid case style for static constant 'singleQubitGates'

    static const auto singleQubitGates = {"id", "u1", "u2", "u3",
                      ^~~~~~~~~~~~~~~~
                      SINGLE_QUBIT_GATES
  

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