Add BaseEstimatorV2 (#11527)

* Add BaseEstimatorV2 class

Taken from 11227, but modified to
- remove options from BaseEstimatorV2
- add precision attribute to BaseEstimatorV2 and EstimatorPub
- remove BasePrimitiveV2 and BasePub

Co-Authored-By: Ikko Hamamura <[email protected]>
Co-Authored-By: Ian Hincks <[email protected]>

* Fix removal of BasePub

* Remove precision from EstimatorPub

* Add BaseEstimator._make_data_bin() static method

* Apply suggestions from code review

Co-authored-by: Ian Hincks <[email protected]>

* Apply suggestions from code review

Co-authored-by: Ian Hincks <[email protected]>

* linting

* Move precision to EstimatorPub and Estimator.run

* Update EstimatorV2 run return type, fix some typos

* Fix some minor problems

* add tests

* Add `*` arg blocker, np.float -> np.float64

* linting

* add test for line of code changed in observables_array.py

---------

Co-authored-by: Ikko Hamamura <[email protected]>
Co-authored-by: Ian Hincks <[email protected]>
Co-authored-by: Ian Hincks <[email protected]>
Co-authored-by: Ian Hincks <[email protected]>

qiskit/primitives/__init__.py

@@ -31,6 +31,7 @@
    BaseEstimator
    Estimator
    BackendEstimator
+   EstimatorPub
 
 Sampler
 =======
@@ -41,6 +42,7 @@
    BaseSampler
    Sampler
    BackendSampler
+   SamplerPub
 
 Results
 =======
@@ -59,6 +61,13 @@
 from .base import BaseEstimator, BaseSampler
 from .base.estimator_result import EstimatorResult
 from .base.sampler_result import SamplerResult
-from .containers import BindingsArray, ObservablesArray, PrimitiveResult, PubResult, SamplerPub
+from .containers import (
+    BindingsArray,
+    ObservablesArray,
+    PrimitiveResult,
+    PubResult,
+    SamplerPub,
+    EstimatorPub,
+)
 from .estimator import Estimator
 from .sampler import Sampler

qiskit/primitives/base/__init__.py

@@ -14,7 +14,7 @@
 Abstract base classes for primitives module.
 """
 
-from .base_estimator import BaseEstimator
 from .base_sampler import BaseSampler, BaseSamplerV2
+from .base_estimator import BaseEstimator, BaseEstimatorV2
 from .estimator_result import EstimatorResult
 from .sampler_result import SamplerResult

qiskit/primitives/base/base_estimator.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2022.
+# (C) Copyright IBM 2022, 2023, 2024.
 #
 # This code is licensed under the Apache License, Version 2.0. You may
 # obtain a copy of this license in the LICENSE.txt file in the root directory
@@ -14,9 +14,79 @@
 
 .. estimator-desc:
 
-=====================
-Overview of Estimator
-=====================
+========================
+Overview of EstimatorV2
+========================
+
+:class:`~BaseEstimatorV2` is a primitive that estimates expectation values for provided quantum
+circuit and observable combinations.
+
+Following construction, an estimator is used by calling its :meth:`~.BaseEstimatorV2.run` method
+with a list of pubs (Primitive Unified Blocs). Each pub contains three values that, together,
+define a computation unit of work for the estimator to complete:
+
+* a single :class:`~qiskit.circuit.QuantumCircuit`, possibly parametrized, whose final state we
+  define as :math:`\psi(\theta)`,
+
+* one or more observables (specified as any :class:`~.ObservablesArrayLike`, including
+  :class:`~.Pauli`, :class:`~.SparsePauliOp`, ``str``) that specify which expectation values to
+  estimate, denoted :math:`H_j`, and
+
+* a collection parameter value sets to bind the circuit against, :math:`\theta_k`.
+
+Running an estimator returns a :class:`~qiskit.providers.JobV1` object, where calling
+the method :meth:`qiskit.providers.JobV1.result` results in expectation value estimates and metadata
+for each pub:
+
+.. math::
+
+    \langle\psi(\theta_k)|H_j|\psi(\theta_k)\rangle
+
+The observables and parameter values portion of a pub can be array-valued with arbitrary dimensions,
+where standard broadcasting rules are applied, so that, in turn, the estimated result for each pub
+is in general array-valued as well. For more information, please check
+`here <https://github.com/Qiskit/RFCs/blob/master/0015-estimator-interface.md#arrays-and
+-broadcasting->`_.
+
+Here is an example of how the estimator is used.
+
+.. code-block:: python
+
+    from qiskit.primitives.statevector_estimator import Estimator
+    from qiskit.circuit.library import RealAmplitudes
+    from qiskit.quantum_info import SparsePauliOp
+
+    psi1 = RealAmplitudes(num_qubits=2, reps=2)
+    psi2 = RealAmplitudes(num_qubits=2, reps=3)
+
+    H1 = SparsePauliOp.from_list([("II", 1), ("IZ", 2), ("XI", 3)])
+    H2 = SparsePauliOp.from_list([("IZ", 1)])
+    H3 = SparsePauliOp.from_list([("ZI", 1), ("ZZ", 1)])
+
+    theta1 = [0, 1, 1, 2, 3, 5]
+    theta2 = [0, 1, 1, 2, 3, 5, 8, 13]
+    theta3 = [1, 2, 3, 4, 5, 6]
+
+    estimator = Estimator()
+
+    # calculate [ <psi1(theta1)|H1|psi1(theta1)> ]
+    job = estimator.run([(psi1, hamiltonian1, [theta1])])
+    job_result = job.result() # It will block until the job finishes.
+    print(f"The primitive-job finished with result {job_result}"))
+
+    # calculate [ [<psi1(theta1)|H1|psi1(theta1)>,
+    #              <psi1(theta3)|H3|psi1(theta3)>],
+    #             [<psi2(theta2)|H2|psi2(theta2)>] ]
+    job2 = estimator.run(
+        [(psi1, [hamiltonian1, hamiltonian3], [theta1, theta3]), (psi2, hamiltonian2, theta2)]
+    )
+    job_result = job2.result()
+    print(f"The primitive-job finished with result {job_result}")
+
+
+========================
+Overview of EstimatorV1
+========================
 
 Estimator class estimates expectation values of quantum circuits and observables.
 
@@ -82,24 +152,36 @@
 
 import warnings
 from abc import abstractmethod
-from collections.abc import Sequence
+from collections.abc import Iterable, Sequence
 from copy import copy
 from typing import Generic, TypeVar
 
-from qiskit.utils.deprecation import deprecate_func
+import numpy as np
+from numpy.typing import NDArray
+
 from qiskit.circuit import QuantumCircuit
 from qiskit.circuit.parametertable import ParameterView
 from qiskit.providers import JobV1 as Job
 from qiskit.quantum_info.operators import SparsePauliOp
 from qiskit.quantum_info.operators.base_operator import BaseOperator
+from qiskit.utils.deprecation import deprecate_func
 
-from .base_primitive import BasePrimitive
+from ..containers import (
+    make_data_bin,
+    DataBin,
+    EstimatorPub,
+    EstimatorPubLike,
+    PrimitiveResult,
+    PubResult,
+)
 from . import validation
+from .base_primitive import BasePrimitive
+from .base_primitive_job import BasePrimitiveJob
 
 T = TypeVar("T", bound=Job)
 
 
-class BaseEstimator(BasePrimitive, Generic[T]):
+class BaseEstimatorV1(BasePrimitive, Generic[T]):
     """Estimator base class.
 
     Base class for Estimator that estimates expectation values of quantum circuits and observables.
@@ -254,3 +336,45 @@ def parameters(self) -> tuple[ParameterView, ...]:
             Parameters, where ``parameters[i][j]`` is the j-th parameter of the i-th circuit.
         """
         return tuple(self._parameters)
+
+
+BaseEstimator = BaseEstimatorV1
+
+
+class BaseEstimatorV2:
+    """Estimator base class version 2.
+
+    An estimator estimates expectation values for provided quantum circuit and
+    observable combinations.
+
+    An Estimator implementation must treat the :meth:`.run` method ``precision=None``
+    kwarg as using a default ``precision`` value.  The default value and methods to
+    set it can be determined by the Estimator implementor.
+    """
+
+    @staticmethod
+    def _make_data_bin(pub: EstimatorPub) -> DataBin:
+        # provide a standard way to construct estimator databins to ensure that names match
+        # across implementations
+        return make_data_bin(
+            (("evs", NDArray[np.float64]), ("stds", NDArray[np.float64])), pub.shape
+        )
+
+    @abstractmethod
+    def run(
+        self, pubs: Iterable[EstimatorPubLike], *, precision: float | None = None
+    ) -> BasePrimitiveJob[PrimitiveResult[PubResult]]:
+        """Estimate expectation values for each provided pub (Primitive Unified Bloc).
+
+        Args:
+            pubs: An iterable of pub-like objects, such as tuples ``(circuit, observables)`` or
+                  ``(circuit, observables, parameter_values)``.
+            precision: The target precision for expectation value estimates of each
+                       run :class:`.EstimatorPub` that does not specify its own
+                       precision. If None the estimator's default precision value
+                       will be used.
+
+        Returns:
+            A job object that contains results.
+        """
+        pass

qiskit/primitives/base/base_sampler.py

@@ -278,7 +278,7 @@ class BaseSamplerV2:
 
     @abstractmethod
     def run(
-        self, pubs: Iterable[SamplerPubLike], shots: int | None = None
+        self, pubs: Iterable[SamplerPubLike], *, shots: int | None = None
     ) -> BasePrimitiveJob[PrimitiveResult[PubResult]]:
         """Run and collect samples from each pub.
 

qiskit/primitives/containers/__init__.py

@@ -16,7 +16,8 @@
 
 from .bindings_array import BindingsArray
 from .bit_array import BitArray
-from .data_bin import make_data_bin
+from .data_bin import make_data_bin, DataBin
+from .estimator_pub import EstimatorPub, EstimatorPubLike
 from .observables_array import ObservablesArray
 from .primitive_result import PrimitiveResult
 from .pub_result import PubResult

qiskit/primitives/containers/data_bin.py

@@ -59,7 +59,7 @@ def make_data_bin(
 
     .. code-block:: python
 
-        my_bin = make_data_bin([("alpha", np.NDArray[np.float])], shape=(20, 30))
+        my_bin = make_data_bin([("alpha", np.NDArray[np.float64])], shape=(20, 30))
 
         # behaves like a dataclass
         my_bin(alpha=np.empty((20, 30)))