Pennylane-qiskit

New features since last release

* Qiskit devices now support custom wire labels.
[(99)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/99)
[(100)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/100)

One can now specify any string or number as a custom wire label,
and use these labels to address subsystems on the device:

python
dev = qml.device('qiskit.ibmq', wires=['q1', 'ancilla', 0, 1])

def circuit():
qml.Hadamard(wires='q1')
qml.CNOT(wires=[1, 'ancilla'])


Improvements

* Adds support for Qiskit v0.20.
[(101)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/101)

Bug fixes

* When converting QASM or Qiskit circuit to PennyLane templates, the `CU1` gate
is now natively supported and converted to a `QubitUnitary`.
[(101)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/101)

Contributors

This release contains contributions from (in alphabetical order):

Maria Schuld, Antal Száva

---

New features since last release

Breaking changes

* Now supports Qiskit version 0.19.1. As a result of breaking changes
within Qiskit, version 0.18 and below are no longer supported.
[(81)](https://github.com/XanaduAI/pennylane-qiskit/pull/81)
[(85)](https://github.com/XanaduAI/pennylane-qiskit/pull/85)
[(86)](https://github.com/XanaduAI/pennylane-qiskit/pull/86)

Improvements

* Ported the `QiskitDevice` class to inherit from the `QubitDevice` class
defined in PennyLane to use unified qubit operations and ease development.
[(83)](https://github.com/XanaduAI/pennylane-qiskit/pull/83)

* Added a test for returning probabilities when using the `IBMQDevice`.
[(82)](https://github.com/XanaduAI/pennylane-qiskit/pull/82)

Documentation

* Major redesign of the documentation, making it easier to navigate.
[(78)](https://github.com/XanaduAI/pennylane-qiskit/pull/78)
[(79)](https://github.com/XanaduAI/pennylane-qiskit/pull/79)

Bug fixes

* Added a type conversion of parameters for parametrized gates, and renamed
various gates for Qiskit version 0.18.0 support.
[(81)](https://github.com/XanaduAI/pennylane-qiskit/pull/81)

* Renamed `QiskitDevice.probabilities` to `QiskitDevice.probability` to overload
`pennylane.Device.probability`. This fixes a bug that raises `NotImplementedError`
when a QNode is used to compute probabilities on a IBMQ device.
[(80)](https://github.com/XanaduAI/pennylane-qiskit/pull/80)


Contributors

This release contains contributions from (in alphabetical order):

Rafael Haenel, Josh Izaac, Maria Schuld, Antal Száva

---

Bug fixes

* Fixed a bug where users with `IBMQ` tokens linked to multiple
providers would experience an error.
[(74)](https://github.com/XanaduAI/pennylane-qiskit/pull/74)

Contributors

This release contains contributions from (in alphabetical order):

Antal Száva

---

Bug fixes

* Fixed a bug where gradient computations always returned 0 when
loading a parametrized Qiskit circuit as a PennyLane template.
[(71)](https://github.com/XanaduAI/pennylane-qiskit/pull/71)

Contributors

This release contains contributions from (in alphabetical order):

Josh Izaac

---

Bug fixes

* Removed v1 `IBMQ` credentials, disallowed `unitary_simulator` backend to
have `memory=True` and discontinuing support for `QubitStateVector` on
the `unitary_simulator` backend due to Qiskit's 0.14.0 version.
[65](https://github.com/XanaduAI/pennylane-qiskit/pull/65)

Contributors

This release contains contributions from (in alphabetical order):

Antal Száva

---

Bug fixes

* Set `analytic=False` as default, since by default warnings are raised
for hardware simulators.
[64](https://github.com/XanaduAI/pennylane-qiskit/pull/64)

Contributors

This release contains contributions from (in alphabetical order):

Antal Száva

---