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@josh146 josh146 released this Sep 9, 2019 · 6 commits to master since this release

New features since last release

  • Adds a new optimizer, qml.QNGOptimizer, which optimizes QNodes using quantum natural gradient descent. See https://arxiv.org/abs/1909.02108 for more details. #295 #311

  • Adds a new QNode method, QNode.metric_tensor(), which returns the block-diagonal approximation to the Fubini-Study metric tensor evaluated on the attached device. #295

  • Sampling support: QNodes can now return a specified number of samples from a given observable via the top-level pennylane.sample() function. To support this on plugin devices, there is a new Device.sample method.

    Calculating gradients of QNodes that involve sampling is not possible. #256

  • default.qubit has been updated to provide support for sampling. #256

  • Added controlled rotation gates to PennyLane operations and default.qubit plugin. #251

Breaking changes

  • The method Device.supported was removed, and replaced with the methods Device.supports_observable and Device.supports_operation. Both methods can be called with string arguments (dev.supports_observable('PauliX')) and class arguments (dev.supports_observable(qml.PauliX)). #276

  • The following CV observables were renamed to comply with the new Operation/Observable scheme: MeanPhoton to NumberOperator, Homodyne to QuadOperator and NumberState to FockStateProjector. #243

Improvements

  • The AmplitudeEmbedding function now provides options to normalize and pad features to ensure a valid state vector is prepared. #275

  • Operations can now optionally specify generators, either as existing PennyLane operations, or by providing a NumPy array. #295 #313

  • Adds a Device.parameters property, so that devices can view a dictionary mapping free parameters to operation parameters. This will allow plugin devices to take advantage of parametric compilation. #283

  • Introduces two enumerations: Any and All, representing any number of wires and all wires in the system respectively. They can be imported from pennylane.operation, and can be used when defining the Operation.num_wires class attribute of operations. #277

    As part of this change:

    • All is equivalent to the integer 0, for backwards compatibility with the existing test suite

    • Any is equivalent to the integer -1 to allow numeric comparison operators to continue working

    • An additional validation is now added to the Operation class, which will alert the user that an operation with num_wires = All is being incorrectly.

  • The one-qubit rotations in pennylane.plugins.default_qubit no longer depend on Scipy's expm. Instead they are calculated with Euler's formula. #292

  • Creates an ObservableReturnTypes enumeration class containing Sample, Variance and Expectation. These new values can be assigned to the return_type attribute of an Observable. #290

  • Changed the signature of the RandomLayer and RandomLayers templates to have a fixed seed by default. #258

  • setup.py has been cleaned up, removing the non-working shebang, and removing unused imports. #262

Documentation

  • A documentation refactor to simplify the tutorials and include Sphinx-Gallery. #291

    • Examples and tutorials previously split across the examples/ and doc/tutorials/ directories, in a mixture of ReST and Jupyter notebooks, have been rewritten as Python scripts with ReST comments in a single location, the examples/ folder.

    • Sphinx-Gallery is used to automatically build and run the tutorials. Rendered output is displayed in the Sphinx documentation.

    • Links are provided at the top of every tutorial page for downloading the tutorial as an executable python script, downloading the tutorial as a Jupyter notebook, or viewing the notebook on GitHub.

    • The tutorials table of contents have been moved to a single quick start page.

  • Fixed a typo in QubitStateVector. #295

  • Fixed a typo in the default_gaussian.gaussian_state function. #293

  • Fixed a typo in the gradient recipe within the RX, RY, RZ operation docstrings. #248

  • Fixed a broken link in the tutorial documentation, as a result of the qml.expval.Observable deprecation. #246

Bug fixes

  • Fixed a bug where a PolyXP observable would fail if applied to subsets of wires on default.gaussian. #277

Contributors

This release contains contributions from (in alphabetical order):

Simon Cross, Aroosa Ijaz, Josh Izaac, Nathan Killoran, Johannes Jakob Meyer, Rohit Midha, Nicolás Quesada, Maria Schuld, Antal Száva, Roeland Wiersema.

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