Mitiq

Summary

This is a patch release to fix two bugs (gh-736, gh-737) related to the integration with optional packages.
It also fixes other minor problems (see the list of changes below).

All Changes

- Patch 0.9.0 (rmlarose, gh-739).
- Make readthedocs succeed in building the pdf with pdflatex (andreamari, gh-743).
- Update energy landscape example in docs (andreamari, gh-742).
- Remove old deprecation warnings (rmlarose, gh-744).

Summary

The main addition introduced in this release is the implementation of a new error mitigation technique: (variable-noise) Clifford data regression ([arXiv:2005.10189](https://arxiv.org/abs/2005.10189), [arXiv:2011.01157](https://arxiv.org/abs/2011.01157)). This is structured as
a Mitiq module called `mitiq.cdr`.

Another important change is the integration with Amazon Braket, such that Mitiq is now compatible with circuits of type `braket.circuits.Circuit`. Moreover all the existing Mitiq integrations are now organized into unique module called `mitiq.interface`.

In the context of probabilistic error cancellation, the sub-module `mitiq.pec.representations` has been significantly improved. Now one can easily compute the optimal quasi-probabiliy representation of an ideal gate as a linear combination of `NoisyOperation` objects.

Thanks to all contributors (L-P-B, Aaron-Robertson, francespoblete, LaurentAjdnik, maxtremblay, andre-a-alves, paniash, purva-thakre) and in particular to the participants of [unitaryHACK](https://2021.unitaryhack.dev/)!

All Changes

- New notation NoisyOperation(circuit, channel_matrix) (andreamari, gh-725).
- Update docs for transforming Qiskit registers (rmlarose, gh-724).
- Remove classical register transformations in Qiskit conversions (Aaron-Robertson, gh-672).
- Change return format for `execute_with_cdr` (rmlarose, gh-722).
- Organize supported packages in `mitiq.interface` (rmlarose, gh-706).
- Change requirements to Cirq 0.10 (andreamari, gh-717).
- Make CDR work with any `QPROGRAM` (rmlarose, gh-718).
- Clearer return type for extrapolate and remove deprecated method (rmlarose, gh-714).
- Update feature request template (rmlarose, gh-713).
- CDR part two - Clifford data regression functions to fit training data (L-P-B gh-677).
- Consolidate images, update README. (rmlarose, gh-709).
- New logo for readme (crazy4pi314, francespoblete, gh-709).
- Update Guidelines for Release (nathanshammah, gh-707).
- Add action to close stale issues/pr 698 (crazy4pi314, gh-699).
- Optimal quasi-probability representations (andreamari, gh-701).
- Update links to Cirq documentation (LaurentAjdnik, gh-704).
- Warning for short programs [unitaryHACK] (Yash-10, gh-700).
- Preparing for optimal representations: Helper functions for channel manipulation. (andreamari, gh-694).
- [UnitaryHACK] Improve conversion from braket to cirq (maxtremblay, gh-688).
- [unitaryHack] Add instructions to solve make docs error for Windows/3.8 users (andre-a-alves, gh-691).
- Add link to docs for source installation in README (paniash, gh-682).
- Mention Braket in the README (andreamari, gh-687).
- [UnitaryHACK] ZNE-PEC uniformity (andre-a-alves, gh-656).
- Minor update of parameter noise scaling (andreamari, gh-684).
- Add braket support via rudimentary translator (rmlarose, gh-590).
- Specify qiskit elements in output of about.py (purva-thakre, gh-674).
- Depend only on cirq-core (rmlarose, gh-673). This was reverted in gh-717.
- Fix docs build (rmlarose, gh-671).
- Fix is_clifford logic for Clifford Data Regression (L-P-B gh-669).

Summary

This release has the following major components:

- Re-implements local folding functions (`zne.scaling.fold_gates_from_left`, `zne.scaling.fold_gates_from_right` and `zne.scaling.fold_gates_at_random`) to make them more uniform at large scale factors and match how they were defined in [Digital zero-noise extrapolation for quantum error mitigation](https://arxiv.org/abs/2005.10921).
- Adds a new noise scaling method, `zne.scaling.fold_all`, which locally folds all gates. This can be used, e.g., to "square CNOTs," a common literature technique, by calling `fold_all` and excluding single-qubit gates.
- Adds functionality for the training portion of [Clifford data regression](https://arxiv.org/abs/2005.10189), specifically to map an input (pre-compiled) circuit to a set of (near) Clifford circuits which are used as training data for the method. The full CDR technique is still in development and will be complete with the addition of regression methods.
- Improves the (sampling) performance of PEC (by a lot!) via fewer circuit conversions.
- Adds `PauliString` object, the first change of several in the generalization of executors. This object is not yet used in any error mitigation pipelines but can be used as a stand-alone.

Additionally, this release

- Fixes some CI components including uploading coverage from master and suppressing nightly Test PyPI uploads on forks.
- Adds links to GitHub on README and RTD.

Special thanks to all contributors - purva-thakre, Aaron-Robertson, andre-a-alves, mstechly, ckissane, HaoTy, briancylui, and L-P-B - for your work on this release!

All Changes

- Remove docs/pdf in favor of RTD (rmlarose, gh-662).
- Redefine and re-implement local folding functions (andreamari, gh-649).
- Move Cirq executors from docs to utilities (purva-thakre, gh-603).
- Add functionality for the training portion of Clifford Data Regression (L-P-B, gh-601).
- Fix custom factory example in docs (andreamari, gh-601).
- Improves PEC sampling speed via fewer conversions (ckissane, HaoTy, briancylui, gh-647).
- Minor typing fixes (mstechly, gh-652).
- Add new `fold_all` scaling method (rmlarose, gh-648).
- Add `PauliString` (rmlarose, gh-633).
- Update information about formatting in RTD (purva-thakre, gh-622).
- Fix typo in getting started guide (andre-a-alves, gh-640).
- Suppress Test PyPI nightly upload on forks (purva-thakre, gh-597).
- Add link to GitHub in README and add octocat link to GitHub on RTD (andre-a-alves, gh-637).
- Move all benchmark circuit generation to `mitiq.benchmarks`, adding option for converions (Aaron-Robertson, gh-632).
- Use `execute_with_shots_and_noise` in Qiskit utils test (Aaron-Robertson, gh-621).
- Install only the Qiskit packages we need (purva-thakre, gh-614).
- Update PR template (rmlarose, gh-634).
- Add blurb about unitaryHACK (nathanshammah).

Summary

This release focuses on contributions from the community.
Many thanks yhindi for adding a method to parametrically scale noise in circuit, to aaron-robertson and pchung39 for adding Qiskit executors with depolarizing noise to the utils,
to purva-thakre for several bug fixes and improvements. Thanks also to BobinMathew and marwahaha for typo corrections.

All Changes

- Pin `docutils` version to solve CI issues (purva-thakre, gh-626)
- Add qiskit executor example for exact density matrix simulation with depolarizing noise (aaron-robertson, gh-574)
- Replace Qiskit utils with Qiskit executors from docs (pchung39, aaron-robertson, gh-584)
- Change custom depolarizing channel in PEC (purva-thakre, gh-615)
- Document codecov fetch depth change and increase codecov action version (grmlarose, gh-618)
- Fix spelling typo (marwahaha, gh-616)
- Add link for MEP (purva-thakre, gh-610)
- Correct a typo in the readme (BobinMathew, gh-609)
- Add `represent_operations_in_circuit_...` functions for PEC (andreamari, gh-515)
- Add qiskit and cirq executor examples gifs to readme (nathanshammah, gh-587)
- Move Cirq executors in docs to cirq_utils (purva-thakre, gh-603)
- Add parametrized scaling (yhindyYousef, gh-411)
- Fix mitiq.about() qiskit version (aaron-robertson, gh-598)
- Fix typo in ZNE documentation (purva-thakre, gh-602)
- Add minimal section on PEC to documentation (nathanshammah andreamari, gh-564)
- Various improvements to CI and testing (rmlarose, gh-583)
- Corrects typo in docs of error mitigation guide (purva-thakre, gh-585)
- Remove factory equality and fix bug in `PolyExpFactory.extrapolate` (rmlarose, gh-580)
- [Bug Fix] Examples (notebooks) in the online documentation now have output code cells (Aaron-Robertson, gh-576)
- Update version to dev (andreamari, gh-572)
- Change custom depolarizing channel in PEC test (purva-thakre, gh-615)

Summary

The automated workflows for builds and releases are improved and PyPI releases are now automated.
We have more documentation on PEC and have a new tutorial on QAOA with Mitiq, as well as some miscellaneous bug fixes.

All Changes

- Add minimal section on PEC to documentation (nathanshammah, gh-564)

- Improve CI and release/patch workflow and documentation (crazy4pi314 gh-566).
- Adding a Mitiq Enhancement Proposal template and process (crazy4pi314 gh-563).
- Add to the documentation papers citing Mitiq, close gh-424 (nathanshammah gh-560).
- Added a new tutorial where MaxCut is solved with a mitigated QAOA (andreamari, gh-562).
- Bumping the version of Qiskit version in `dev_requirements` (andreamari gh-554)
- Retain measurement order when folding Qiskit circuits (rmlarose gh-557)
- Standardize and touch up docs (rmlarose gh-553)
- Adding make doc-clean command (crazy4pi314 gh-549)
- Fix and refactor RB circuits function (rmlarose gh-539)
- Improve GateOperation simplification in exponents (rmlarose gh-541)

Summary

The implementation of Probabilistic Error Cancellation is now multi-platform and
documented in the docs (for the moment only in the _Getting Started_ section).
A new infrastructure based on [MyST](https://myst-parser.readthedocs.io/en/stable/)
can now be used for writing the documentation and, in particular, for adding new examples
in the _Mitiq Examples_ section.

All Changes

- Adding documentation section for examples, support for Jyupyter notebooks (crazy4pi314, gh-509).
- Add minimal documentation for PEC in the Getting Started (andreamari, gh-532).
- Optionally return a dictionary with all pec data in execute_with_pec (andreamari, gh-518).
- Added local_depolarizing_representations and Choi-based tests (andreamari, gh-502).
- Add multi-platform support for PEC (rmlarose, gh-500).
- Added new `plot_data` and `plot_fit` methods for factories(crazy4pi314 elmandouh, gh-333).
- Fixes random failure of PEC sampling test(rmlarose, gh-481).
- Exact copying of shell commands, update make target for pdf and update development version(rmlarose, gh-469).
- Add a new FakeNodesFactory class based on an alternative interpolation method (elmandouh, gh-444).
- Add parameter calibration method to find base noise for parameter noise (yhindy, gh-411).
- Remove duplication of the reduce method in every (non-adaptive) factory (elmandouh, gh-470).