Release notes for Terra 0.21rc1 (#8227)

* Fix typos in release notes

* Remove release notes from 0.20.x patches

* Update releasenotes/notes/delay-fake-backends-3f68c074e85d531f.yaml

* Update add_check_from_sparse_list-97f13fde87c7bcb6.yaml

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

releasenotes/notes/add-group-commuting-method-in-PauliList-and-SparsePauliOp-5dec2877c4a97861.yaml

@@ -5,8 +5,6 @@ features:
     which partition these operators into sublists where each element commutes with all the others.
     For example::
 
-    .. code-block:: python
-
       from qiskit.quantum_info import PauliList, SparsePauliOp
 
       groups = PauliList(["XX", "YY", "IZ", "ZZ"]).group_commuting()

releasenotes/notes/add-overloading@-3fedb7bc2fd4d7f7.yaml

@@ -1,14 +1,6 @@
 ---
 features:
   - |
-    Adds a ``@`` (``__matmul__``) binary operator to ``BaseOperator`` subclasses
+    Added the ``@`` (``__matmul__``) binary operator to ``BaseOperator`` subclasses
     in the :mod:`qiskit.quantum_info` module. This is shorthand to call the
-    classes ``dot`` method (``A @ B == A.dot(B)``).
-
-    Example
-
-    .. code:: python
-    
-      from qiskit.quantum_info import Pauli
-
-      Pauli("X") @ Pauli("Y")
+    classes' ``dot`` method (``A @ B == A.dot(B)``).

releasenotes/notes/add-serializable-parametric-pulse-31490c4d2cc49ec6.yaml

@@ -1,22 +1,20 @@
 ---
 features:
   - |
-    New pulse base class :class:`~SymbolicPulse` has been added. This is a
-    replacement of the conventional :class:`~ParametricPulse` which will be deprecated.
-    In new base class, pulse envelope and parameter validation functions are
-    represented by symbolic expression objects, which are lambidfied immediately when
-    corresponding methods are called for the first time.
-    The new class provides a self-contained and portable pulse data since these symbolic equations
+    Added a new pulse base class :class:`.SymbolicPulse`. This is a
+    replacement of the conventional :class:`.ParametricPulse`, which will be deprecated.
+    In the new base class, pulse-envelope and parameter-validation functions are
+    represented by symbolic-expression objects.
+    The new class provides self-contained and portable pulse data since these symbolic equations
     can be easily serialized through symbolic computation libraries.
-    QPY serialization support of these pulses is planned.
 upgrade:
   - |
-    Importing pulse class from ``qiskit.pulse.library.*`` now import :class:`~SymbolicPulse`
-    subclass rather than :class:`~ParametricPulse` subclass.
-    There are same set of pulse subclass in the symbolic pulse module,
+    The pulse classes in :mod:`qiskit.pulse.library` are now subclasses of
+    :class:`.SymbolicPulse` rather than :class:`.ParametricPulse`.  The available
+    classes remain unchanged as
     :class:`~qiskit.pulse.library.Gaussian`,
     :class:`~qiskit.pulse.library.GaussianSquare`,
     :class:`~qiskit.pulse.library.Drag`, and
     :class:`~qiskit.pulse.library.Constant`.
-    Becasue :class:`~SymbolicPulse` supports full backward compatibility,
-    there is no loss of functionality due to the switching of the base class.
+    :class:`.SymbolicPulse` has full backward compatibility, and there should be
+    no loss of functionality.

releasenotes/notes/add-support-non-hermitian-op-aerpauliexpectation-653d8e16de4eca07.yaml

@@ -1,5 +1,5 @@
 features:
   - |
-    Added the support of non-hermitian operators for :class:`~qiskit.opflow.AerPauliExpectation`.
-    This for instance enables using Aer's fast snapshot expectation value in algorithms such as
-    :class:`~qiskit.algorithms.QEOM`.
+    Added support for non-Hermitian operators in :class:`.AerPauliExpectation`.
+    This allows the use of Aer's fast snapshot expectation computations in
+    algorithms such as :class:`~qiskit.algorithms.QEOM`.

releasenotes/notes/add_check_from_sparse_list-97f13fde87c7bcb6.yaml

@@ -1,6 +1,6 @@
 ---
-features:
+fixes:
   - |
-    Allow checking for duplicate qubit indices in :meth:`~qiskit.quantum_info.SparsePauliOp.from_sparse_list`.
-    The checks can be turned off by setting the new keyword argument ``do_checks`` to ``False`` 
-    (it  is ``True`` per default).
+    Duplicate qubit indices given to :meth:`.SparsePauliOp.from_sparse_list` will now
+    correctly raise an error, instead of silently overwriting previous values.
+    The old behavior can be accessed by passing the new keyword argument ``do_checks=False``.

releasenotes/notes/change-instruction-data-scalar-81f2066ca2435933.yaml

@@ -3,14 +3,14 @@ upgrade:
   - |
     The data type of each element in :attr:`.QuantumCircuit.data` has changed.
     It used to be a simple 3-tuple of an :class:`~.circuit.Instruction`, a list
-    of :class:`.Qubit`\ s, and a list of `:class:`.Clbit`\ s, whereas it is now
+    of :class:`.Qubit`\ s, and a list of :class:`.Clbit`\ s, whereas it is now
     an instance of :class:`.CircuitInstruction`.
 
     The attributes of this new class are :attr:`~.CircuitInstruction.operation`,
     :attr:`~.CircuitInstruction.qubits` and :attr:`~.CircuitInstruction.clbits`,
     corresponding to the elements of the previous tuple.  However,
     :attr:`~.CircuitInstruction.qubits` and :attr:`~.CircuitInstruction.clbits`
-    are now `tuple` instances, not `list`\ s.
+    are now ``tuple`` instances, not ``list``\ s.
 
     This new class will behave exactly like the old 3-tuple if one attempts to
     access its index its elements, or iterate through it.  This includes casting

releasenotes/notes/cleanup-timeline-drawer-a6287bdab4459e6e.yaml

@@ -1,14 +1,12 @@
 ---
 features:
   - |
-    New attribute :attr:`op_start_times` has been added to :class:`~QuantumCircuit`.
-    This information is populated when one of scheduling analysis passes is run on the circuit.
-    It can be used to obtain circuit instruction with instruction time, for example:
-
-    .. code-block:: python
+    A new attribute :attr:`.QuantumCircuit.op_start_times` 
+    is populated when one of scheduling analysis passes is run on the circuit.
+    It can be used to obtain circuit instruction with instruction time, for example::
 
       from qiskit import QuantumCircuit, transpile
-      from qiskit.test.mock import FakeMontreal
+      from qiskit.providers.fake_provider import FakeMontreal
 
       backend = FakeMontreal()
 
@@ -23,11 +21,12 @@ features:
 
 fixes:
   - |
-    Time misalignment bug of drawing classical register with :func:`~timeline_drawer`
-    has been fixed. Now classical register slots are drawn at correct position.
+    The :func:`.timeline_drawer` visualization will no longer misalign classical
+    register slots.
 deprecations:
   - |
-    Calling :func:`~timeline_drawer` with unscheduled circuit has been deprecated.
-    All circuits, e.g. even though one consisting only of delay instructions,
-    must be transpiled with ``scheduling_method`` option to generate
-    schedule information being stored in :attr:`QuantumCircuit.op_start_times`.
+    Calling :func:`.timeline_drawer` with an unscheduled circuit has been deprecated.
+    All circuits, even one consisting only of delay instructions,
+    must be transpiled with the ``scheduling_method`` keyword argument of
+    :func:`.transpile` set, to generate schedule information being stored in
+    :attr:`.QuantumCircuit.op_start_times`.

releasenotes/notes/clear-circuit-b8edd4126f47d75a.yaml

@@ -1,13 +1,11 @@
 ---
 features:
   - |
-    Added a new method :py:meth:`.QuantumCircuit.clear` which is used to to erase all instructions
-    from a QuantumCircuit. We clear both the data and the parameter table.
+    Added a new method :meth:`.QuantumCircuit.clear` which is used to remove all instructions
+    from a :class:`.QuantumCircuit`.
   - |
-    Added a new method :py:meth:`QuantumCircuit.copy_empty_like` which is used to get a cleared copy of a
-    :class:`~.QuantumCircuit` instnace. This is logically equivalent to `qc.copy().clear()` however, it is done
-    avoiding a deepcopy of the original QuantumCircuit, and therefore it is more efficient. This functionality
-    already implemented for :class:`~.DAGCircuit`, and retains all relevant circuit properties other than the
-    instructions and associated parameters (e.g. registers, bits, name, metadata). Unlike the
-    :meth:`.DAGCircuit.copy_empty_like` method, this new :class:`~.QuantumCircuit` method allows for
-    an optional parameter to update the name of the copied circuit, mimicking ``qc.copy(name)``.
+    Added a new method :meth:`.QuantumCircuit.copy_empty_like` which is used to get a cleared copy of a
+    :class:`~.QuantumCircuit` instance. This is logically equivalent to ``qc.copy().clear()``, but
+    significantly faster and more memory-efficient.  This is useful when one needs a new empty
+    circuit with all the same resources (qubits, classical bits, metadata, and so on) already
+    added.

releasenotes/notes/delay-fake-backends-3f68c074e85d531f.yaml

@@ -1,12 +1,8 @@
 ---
 fixes:
   - |
-    The :class:`~.BackendV2` based fake backends in
+    The :class:`~.BackendV2`\ -based fake backends in
     the :mod:`qiskit.providers.fake_provider` module, such as
-    ``FakeMontrealV2``, previously were missing the :class:`~qiskit.circuit.Delay` operation
-    support from their :attr:`~.BackendV2.target` attribute. This prevented
-    compiling some :class:`~.QuantumCircuit` objects that contained
-    :class:`~qiskit.circuit.Delay` instructions to these backends. This has been corrected
-    by adding the :class:`~qiskit.circuit.Delay` to the :class:`~.Target` object for each
-    fake backend to ensure that the compiler knows that :class:`~qiskit.circuit.Delay` is
-    a valid operation on the fake backends.
+    :class:`.FakeMontrealV2`, now support the :class:`~qiskit.circuit.Delay` operation
+    in their :attr:`~.BackendV2.target` attributes.  Previously, :class:`.QuantumCircuit` objects
+    that contained delays could not be compiled to these backends.

releasenotes/notes/deprecate-nx-dag-f8a8d947186222c2.yaml

@@ -1,17 +1,17 @@
 ---
 deprecations:
   - |
-    The `NetworkX <https://networkx.org/>`_  converter function for the
-    :class:`~.DAGCircuit`, :meth:`~.DAGCircuit.to_networkx` and
+    The `NetworkX <https://networkx.org/>`__  converter functions for the
+    :meth:`.DAGCircuit.to_networkx` and
     :meth:`~.DAGCircuit.from_networkx`, along with the
     :meth:`.DAGDependency.to_networkx` method have been deprecated and will be
     removed in a future release. Qiskit has been using
     `retworkx <https://qiskit.org/documentation/retworkx/>`__ as its graph
-    library since the qiskit-terra 0.12.0 release and since then the networkx
-    converter function have been a lossy process. They were originally added so
-    that users could leverage NetworkX's algorithms library to leverage
-    functionality not present in retworkx. Since that time retworkx has matured
-    and offers more functionality and the :class:`~.DAGCircuit` is tightly
+    library since the qiskit-terra 0.12.0 release, and since then the networkx
+    converter functions have been lossy. They were originally added so
+    that users could leverage functionality in NetworkX's algorithms library
+    not present in retworkx.  Since that time, retworkx has matured
+    and offers more functionality, and the :class:`~.DAGCircuit` is tightly
     coupled to retworkx for its operation. Having these converter methods
     provides limited value moving forward and are therefore going to be
     removed in a future release.

releasenotes/notes/feature-trotter-qrte-f7b28c4fd4b361d2.yaml

@@ -1,23 +1,17 @@
 ---
 features:
   - |
-    Added Trotterization-based Quantum Real Time Evolution Algorithm
-    :class:`qiskit.algorithms.TrotterQRTE`. It is compliant with the new Quantum Time Evolution
-    Framework and makes use of :class:`qiskit.synthesis.evolution.ProductFormula` and
-    :class:`qiskit.circuit.library.PauliEvolutionGate` implementations.
+    Added a Trotterization-based quantum real-time evolution algorithm
+    :class:`qiskit.algorithms.TrotterQRTE`. It is compliant with the new quantum time evolution
+    framework and makes use of the :class:`.ProductFormula` and
+    :class:`.PauliEvolutionGate` implementations.
 
     .. code-block:: python
 
       from qiskit.algorithms import EvolutionProblem
-      from qiskit.algorithms.evolvers.trotterization import (
-          TrotterQRTE,
-      )
-      from qiskit.opflow import (
-          X,
-          Z,
-          StateFn,
-          SummedOp,
-      )
+      from qiskit.algorithms.evolvers.trotterization import TrotterQRTE
+      from qiskit.opflow import X, Z, StateFn, SummedOp
+
       operator = SummedOp([X, Z])
       initial_state = StateFn([1, 0])
       time = 1

releasenotes/notes/fix-eigs_bounds-function-in-TridiagonalToeplitz-class-52cfad8f72ae7341.yaml

@@ -1,7 +1,7 @@
 ---
 fixes:
   - |
-    Fix a bug in TridiagonalToeplitz.eigs_bounds() method, which caused
-    a returning of wrong eigenvalues bounds in some cases with negative
-    eigenvalues. Refer to `#7939 <https://github.com/Qiskit/qiskit-terra/issues/7939>` 
-    for more details.
+    Fixed a bug in :meth:`.TridiagonalToeplitz.eigs_bounds`, which caused
+    incorrect eigenvalue bounds to be returned in some cases with negative
+    eigenvalues. Refer to `#7939 <https://github.com/Qiskit/qiskit-terra/issues/7939>`__
+    for more details.

releasenotes/notes/fix-latex-ket-max-size-f11c3a89215a49e7.yaml

@@ -1,5 +1,5 @@
 ---
 fixes:
   - |
-    Fixed a bug in which the latex state vector drawer ignores the `max_size`
+    Fixed a bug in which the LaTeX statevector drawer ignored the ``max_size``
     parameter.

releasenotes/notes/fix-qpy-controlled-gates-e653cbeee067f90b.yaml

@@ -14,7 +14,7 @@ fixes:
     :class:`~.ControlledGate` objects. Previously, an exception would be raised
     by :func:`.qpy.load` when trying to reconstruct the custom
     :class:`~.ControlledGate`.
-    Fixed `#7999 <https://github.com/Qiskit/qiskit-terra/issues/7999>`__
+    Fixed `#7999 <https://github.com/Qiskit/qiskit-terra/issues/7999>`__.
   - |
     Fixed support for QPY serialization (:func:`.qpy.dump`) and deserialization
     (:func:`.qpy.load`) of a :class:`~.QuantumCircuit` object containing custom

releasenotes/notes/fix-t2-configurablefakebackend-8660ab3d7a57a824.yaml

@@ -1,5 +1,5 @@
 ---
 fixes:
   - |
-    Fixed the ``t2`` attribute of ``qiskit.providers.fake_provider.ConfigurableFakeBackend``,
-    which was previously incorrectly set based on the provided ``t1``.
+    Fixed the :attr:`.ConfigurableFakeBackend.t2` attribute,
+    which was previously incorrectly set based on the provided ``t1`` value.

releasenotes/notes/fix-target-dt-4d306f1e9b07f819.yaml

@@ -1,8 +1,8 @@
 ---
 fixes:
   - |
-    Fixed an issue with :class:`~.BackendV2` based fake backend classes from the 
-    ``qiskit.providers.fake_provider`` module such as ``FakeMontrealV2`` where the
+    Fixed an issue with :class:`~.BackendV2`\ -based fake backend classes from the 
+    :mod:`qiskit.providers.fake_provider` module such as :class:`.FakeMontrealV2` where the
     value for the :attr:`~.BackendV2.dt` attribute (and the :attr:`.Target.dt` attribute) 
     were not properly being converted to seconds. This would cause issues when
     using these fake backends with scheduling.