Deprecate passing backend as a string (#1804)

* Deprecate passing backend as a string

* add release note

qiskit_ibm_runtime/batch.py

@@ -18,6 +18,7 @@
 
 from qiskit_ibm_runtime import QiskitRuntimeService
 from .session import Session
+from .utils.deprecation import issue_deprecation_msg
 
 
 class Batch(Session):
@@ -98,6 +99,14 @@ def __init__(
         Raises:
             ValueError: If an input value is invalid.
         """
+        if isinstance(backend, str):
+            issue_deprecation_msg(
+                msg="Passing a backend as a string is deprecated",
+                version="0.26.0",
+                remedy="Use the actual backend object instead.",
+                period="3 months",
+            )
+
         super().__init__(service=service, backend=backend, max_time=max_time)
 
     def _create_session(self) -> Optional[str]:

qiskit_ibm_runtime/estimator.py

@@ -163,6 +163,12 @@ def __init__(
                 " the service using `QiskitRuntimeService().backend('ibm_backend')`",
                 3,
             )
+            issue_deprecation_msg(
+                msg="Passing a backend as a string is deprecated",
+                version="0.26.0",
+                remedy="Use the actual backend object instead.",
+                period="3 months",
+            )
         if mode is None:
             mode = session if backend and session else backend if backend else session
         BasePrimitiveV2.__init__(self, mode=mode, options=options)

qiskit_ibm_runtime/sampler.py

@@ -122,6 +122,14 @@ def __init__(
                 " the service using `QiskitRuntimeService().backend('ibm_backend')`",
                 3,
             )
+            issue_deprecation_msg(
+                msg="Passing a backend as a string is deprecated",
+                version="0.26.0",
+                remedy="Use the actual backend object instead.",
+                period="3 months",
+                stacklevel=2,
+            )
+
         if mode is None:
             mode = session if backend and session else backend if backend else session
         BasePrimitiveV2.__init__(self, mode=mode, options=options)

qiskit_ibm_runtime/session.py

@@ -130,6 +130,12 @@ def __init__(
                     else QiskitRuntimeService.global_service
                 )
             if isinstance(backend, str):
+                issue_deprecation_msg(
+                    msg="Passing a backend as a string is deprecated",
+                    version="0.26.0",
+                    remedy="Use the actual backend object instead.",
+                    period="3 months",
+                )
                 self._backend = self._service.backend(backend)
             elif backend is None:
                 raise ValueError('"backend" is required')

release-notes/unreleased/1804.deprecation.rst

@@ -0,0 +1,2 @@
+Passing in a backend as a string into ``Session``, ``Batch``, ``EstimatorV2``, and ``SamplerV2``
+has been deprecated. Use the actual backend object instead.