Release v0.11.0

Changelog

Version 0.11.0 (November 3rd, 2021)

Summary

This release introduces Observables as a major new feature to the Mitiq workflow and a few breaking changes. Support
for Pennylane has been added by adding pennylane.QuantumTapes to mitiq.QPROGRAM.

New features

• Specify and use a mitiq.Observable in any error-mitigation technique.

  • This means the executor function does not have to return the expectation value as a float anymore, but rather
    can return a mitiq.QuantumResult - i.e., an object from which the expectation value can be computed provided
    an observable.
  • The executor function can still return a float, in which case the Observable does not need to be specified
    (and should not be specified).

• All error mitigation techniques can now use batching with the same interface.

• PEC can be run with only a subset of representations of the gates in a circuit. In other words, if the circuit has
  two gates, H and CNOT, you can run execute_with_pec by only providing an OperationRepresentation for, e.g.,
  the CNOT.

  • Before, you had to provide all representations or an error would be raised.
  • Performance of PEC may be better by providing all OperationRepresentations. This change is only with respect to
    usability and not performance.

• Circuits written in Pennylane (as QuantumTapes) are now recognized and suppported by Mitiq.

Breaking changes

• Signatures of execute_with_xxx error-mitigation techniques have changed to include Observables. The default value
  is None, meaning that the executor should return a float as in the old usage, but the additional argument and
  change to keyword-only arguments (see below) may require you to make updates.

• You must now use provide keywords for technique-specific arguments in error mitigation techniques. Example:

# Example new usage of providing keyword arguments. Do this.
execute_with_pec(circuit, executor, observable, representations=representations)

instead of

# Old usage. Don't do this. Technique-specific arguments like `representations` are now keyword-only.
execute_with_pec(circuit, executor, observable, representations)

The latter will raise # TypeError: execute_with_pec() missing 1 required keyword-only argument: 'representations'.

• The first argument of execute_with_zne is now circuit instead of qp to match signatures of other
  execute_with_xxx functions.

All Changes

• Increase shots in test_zne.py (@andreamari, gh-1011)
• Refactor qp to circuit in execute_with_zne (@rmlarose, gh-1009)
• Add Observable documentation and Observable.from_pauli_string_collections method (@rmlarose, gh-1007)
• Executor docs (@rmlarose, gh-1008)
• Bump qiskit to version 0.31 and pin it explicitly in dev requirements (@andreamari, gh-993)
• Use Executor.evaluate for batching in ZNE (@rmlarose, gh-1005)
• Add Executor.evaluate and use for batched execution (@rmlarose, gh-1001)
• Bump PyQuil (@rmlarose, gh-992)
• CDR with Observables (@rmlarose, gh-985)
• Fix bug in OperationRepresentation printing (@andreamari, gh-975)
• Ignore patch releases in dependabot (@rmlarose, gh-981)
• Update pydata-sphinx-theme requirement from ~=0.6.3 to ~=0.7.1 (@dependabot, gh-962)
• Update flake8 requirement from ~=3.9.2 to ~=4.0.1 (@dependabot, gh-982)
• Add PennyLane to frontend table in the readme (@andreamari, gh-973)
• Update amazon-braket-sdk requirement from ~=1.9.1 to ~=1.9.5 (@dependabot, gh-970)
• Update pytest-cov requirement from ~=2.12.1 to ~=3.0.0 (@dependabot, gh-963)
• Fix pip package resolving problems (@andreamari, gh-976)
• Add support for pennylane circuits (everybody and their grandmother, gh-836)
• Keyword only arguments in execute_with_technique functions (@rmlarose, gh-971)
• Foldability check includes a check for inverse (@purva-thakre, gh-939)
• Bump actions/github-script from 3 to 5 (@dependabot, gh-969)
• PEC with Observables & skip operations without known representations (@rmlarose, gh-954)
• Update qiskit-terra requirement from ~=0.18.2 to ~=0.18.3 (@dependabot, gh-955)
• Add observable to zne_decorator (@rmlarose, gh-967)
• Update qiskit-ibmq-provider requirement from ~=0.16.0 to ~=0.17.0 (@dependabot, gh-965)
• Binder badge workflow (@AkashNarayanan, gh-964)
• Fix links and typos in vqe-pyquil-demo.myst and pyquil_demo.myst (@Misty-W, gh-959)
• ZNE with Observables (@rmlarose, gh-948)
• Add PauliString multiplication (@rmlarose, gh-949)
• Update amazon-braket-sdk requirement from ~=1.9.0 to ~=1.9.1 (@dependabot, gh-950)
• Fixing changelog and improving release documentation (@crazy4pi314, gh-946)
• Update version to 0.11.0dev (@rmlarose, gh-947)
• Update pytest-xdist[psutil] requirement from ~=2.3.0 to ~=2.4.0 (@dependabot, gh-938)
• Fix AWS example by fixing a bug in mirror circuits (@andreamari, gh-940)
• Bump codecov/codecov-action from 2.0.3 to 2.1.0 (@dependabot, gh-922)
• Improve OperationRepresentation printing (@andreamari, gh-901)
• Updating release process (@crazy4pi314, gh-936)

Huge thanks to all contributors on this release! @Misty-W, @AkashNarayanan, @purva-thakre, @trbromley, @nathanshammah,
@crazy4pi314, @andreamari, and @rmlarose.