Add support for v2 provider interface (qiskit-community/qiskit-aqua#1270

)

* Add support for v2 provider interface

In Qiskit#5086 the v2 provider interface is being added.
This starter interface is basically a drop in replacement for the v1
interface with 3 changes it's explicitly versioned at the object level,
Backend.run() can take in a circuit object, and Job objects can also be
async or sync. Eventually the interace will likely evolve towards a
model similar to what was initially done in Qiskit#4885.
This commit adds initial support for v2 provider backend objects, the
explicit type checking for BaseBackend objects is blocking the terra PR
from moving forward (because it switched BasicAer to use the v2
interface). This initial support just means accepting v2 Backend objects
in addition to v1 BaseBackend objects.

Depends on Qiskit#5086

* Fix import path

* fix style

Co-authored-by: Manoel Marques <manoel.marques@ibm.com>

qiskit/aqua/operators/converters/circuit_sampler.py

@@ -18,6 +18,7 @@
 from time import time
 
 from qiskit.providers import BaseBackend
+from qiskit.providers import Backend
 from qiskit.circuit import QuantumCircuit, Parameter, ParameterExpression
 from qiskit import QiskitError
 from qiskit.aqua import QuantumInstance
@@ -48,7 +49,7 @@ class CircuitSampler(ConverterBase):
     """
 
     def __init__(self,
-                 backend: Union[BaseBackend, QuantumInstance] = None,
+                 backend: Union[Backend, BaseBackend, QuantumInstance] = None,
                  statevector: Optional[bool] = None,
                  param_qobj: bool = False,
                  attach_results: bool = False) -> None:
@@ -101,7 +102,7 @@ def _check_quantum_instance_and_modes_consistent(self) -> None:
                              'backend, not {}.'.format(self.quantum_instance.backend))
 
     @property
-    def backend(self) -> BaseBackend:
+    def backend(self) -> Union[Backend, BaseBackend]:
         """ Returns the backend.
 
         Returns:
@@ -110,11 +111,11 @@ def backend(self) -> BaseBackend:
         return self.quantum_instance.backend
 
     @backend.setter
-    def backend(self, backend: BaseBackend):
+    def backend(self, backend: Union[Backend, BaseBackend]):
         """ Sets backend without additional configuration. """
         self.set_backend(backend)
 
-    def set_backend(self, backend: BaseBackend, **kwargs) -> None:
+    def set_backend(self, backend: Union[Backend, BaseBackend], **kwargs) -> None:
         """ Sets backend with configuration.
 
         Raises:
@@ -133,13 +134,14 @@ def quantum_instance(self) -> QuantumInstance:
         return self._quantum_instance
 
     @quantum_instance.setter
-    def quantum_instance(self, quantum_instance: Union[QuantumInstance, BaseBackend]) -> None:
+    def quantum_instance(self, quantum_instance: Union[QuantumInstance,
+                                                       Backend, BaseBackend]) -> None:
         """ Sets the QuantumInstance.
 
         Raises:
             ValueError: statevector or param_qobj are True when not supported by backend.
         """
-        if isinstance(quantum_instance, BaseBackend):
+        if isinstance(quantum_instance, (Backend, BaseBackend)):
             quantum_instance = QuantumInstance(quantum_instance)
         self._quantum_instance = quantum_instance
         self._check_quantum_instance_and_modes_consistent()

qiskit/aqua/operators/expectations/expectation_factory.py

@@ -17,6 +17,7 @@
 
 from qiskit import BasicAer
 from qiskit.providers import BaseBackend
+from qiskit.providers import Backend
 from qiskit.aqua.utils.backend_utils import (is_statevector_backend,
                                              is_aer_qasm,
                                              has_aer)
@@ -38,7 +39,7 @@ class ExpectationFactory:
 
     @staticmethod
     def build(operator: OperatorBase,
-              backend: Optional[Union[BaseBackend, QuantumInstance]] = None,
+              backend: Optional[Union[Backend, BaseBackend, QuantumInstance]] = None,
               include_custom: bool = True) -> ExpectationBase:
         """
         A factory method for convenient automatic selection of an Expectation based on the