Pennylane-qiskit

New features since last release

* Added the ability to automatically convert Qiskit `QuantumCircuits`
or QASM circuits directly into PennyLane templates. The loaded
operations can be used directly inside PennyLane circuits.
[55](https://github.com/XanaduAI/pennylane-qiskit/pull/55)

* Updated the list of operations such that each operation is now
used from PennyLane. Added capability to specify the inverses
of operations.
[58](https://github.com/XanaduAI/pennylane-qiskit/pull/58)

Improvements

* Added integration tests for converting objects from Qiskit
using PennyLane.
[57](https://github.com/XanaduAI/pennylane-qiskit/pull/57)

* Added warnings for hardware simulators using `analytic==True`
when calculating expectations and variances.
[59](https://github.com/XanaduAI/pennylane-qiskit/pull/59)

Bug fixes

* Removed `gates.py` including operations `Rot` and `BasisState`
such that these operations are decomposed by PennyLane and no
errors arise for the `BasisState` initialized with all-zero states.
[60](https://github.com/XanaduAI/pennylane-qiskit/pull/60)

Contributors

This release contains contributions from (in alphabetical order):

Antal Száva

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New features since last release

* All Qiskit devices now support tensor observables using the
`return expval(qml.PauliZ(0) qml.Hermitian(A, [1, 2]))`
syntax introduced in PennyLane v0.6.

Contributors

This release contains contributions from (in alphabetical order):

Josh Izaac

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Bug fixes

* Fixed a bug where backend keyword arguments, such as `backend_options`
and `noise_model`, were being passed to backends that did not support it.
[51](https://github.com/XanaduAI/pennylane-qiskit/pull/51)

Contributors

This release contains contributions from (in alphabetical order):

Josh Izaac

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This is a significant release, bringing the plugin up to date with the latest
PennyLane and Qiskit features.

New features since last release

* The plugin and the tests have been completely re-written from scratch, to ensure
high quality and remove technical debt.
[44](https://github.com/XanaduAI/pennylane-qiskit/pull/44)
[43](https://github.com/XanaduAI/pennylane-qiskit/pull/43)

* Samples and variance support have been added to all devices.
[46](https://github.com/XanaduAI/pennylane-qiskit/pull/46)

* Multi-qubit hermitian observables are now supported, due to
support being added in Qiskit version 0.12.

* Support has been added for IBM Q Experience 2.0.
[44](https://github.com/XanaduAI/pennylane-qiskit/pull/44)

Improvements

* Hardware and software devices are now treated identically, with expectations,
variance, and samples computed via the _probability_, not the amplitudes.
This has several consequences:

- It makes the code cleaner and simpler, as there is now one defined
way of computing statistics.

- It is faster in most cases, as this does not require computing
large matrix-vector products, or Kronecker products. Instead,
eigenvalues of single- and multi-qubit observables are computed using
dyanamic programming.

- It reduces the number of tests required.

* Test suite now includes tests against the IBM Q Experience, in addition
to the local simulators.

Bug fixes

* Due to the move to IBM Q 2.0 credentials, users remaining with IBM Q v1.0
now must pass an additional URL argument to the service. The plugin
has been modified to allow the user to pass this argument if required.
[44](https://github.com/XanaduAI/pennylane-qiskit/pull/44)

Contributors
This release contains contributions from:

Shahnawaz Ahmed, Josh Izaac

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New features since last release

- Added noise model and backend options to the devices as well as new observables.
- Added support for all PennyLane observables for calculating expectation values.
- Added (copied & adjusted from pennylane-forest) test for the expectation values.
- Added the necessary DefaultQubit device for comparison.
- Added logging.

Improvements

- Changed expval_queue to obs_queue and expectations to observables as per latest pennylane.
- Reversed qregs to match the default qubit device behavior.
- Renamed devices correctly.
- Made wires explicit. If num_wires of operation is 0 then use the whole system as wires!
- Renamed the IBMQ device from `qiskit.ibm` to `qiskit.ibmq`.

Fixed

- Fixed the Unitary gate.
- Fixed the token loading and the shots.
- Fixed and updated to qiskit v0.10.1
- Fixed the valid expectation values of all devices. Along with it tests where fixed.

Removed

- Removed the IBMQX_TOKEN import and replace with the correct args.
- Removed the unconditional make coverage.
- Removed default qubit device, this is not tested in this package!

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Removed

- Removed the `LegacySimulatorsQiskitDevice` as this isn't supported in `qiskit` anymore.

Improvements

- updated to `qiskit` version `0.10.*`.

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