Adds target kwarg to tomography init (qiskit-community#1025)

This allows specifying a custom target for analysis when initializing the experiments. If set to None automatic target calculation is disabled.

Co-authored-by: Will Shanks <wshaos@posteo.net>

qiskit_experiments/library/tomography/qpt_experiment.py

@@ -64,6 +64,7 @@ def __init__(
         basis_indices: Optional[Sequence[Tuple[List[int], List[int]]]] = None,
         qubits: Optional[Sequence[int]] = None,
         analysis: Union[BaseAnalysis, None, str] = "default",
+        target: Union[Statevector, DensityMatrix, None, str] = "default",
     ):
         """Initialize a quantum process tomography experiment.
 
@@ -94,6 +95,10 @@ def __init__(
             analysis: Optional, a custom analysis instance to use. If ``"default"``
                 :class:`~.ProcessTomographyAnalysis` will be used. If None no analysis
                 instance will be set.
+            target: Optional, a custom quantum state target for computing the
+                state fidelity of the fitted density matrix during analysis.
+                If "default" the state will be inferred from the input circuit
+                if it contains no classical instructions.
         """
         if analysis == "default":
             analysis = ProcessTomographyAnalysis()
@@ -115,7 +120,9 @@ def __init__(
 
         # Set target quantum channel
         if isinstance(self.analysis, TomographyAnalysis):
-            self.analysis.set_options(target=self._target_quantum_channel())
+            if target == "default":
+                target = self._target_quantum_channel()
+            self.analysis.set_options(target=target)
 
     def _target_quantum_channel(self) -> Union[Choi, Operator]:
         """Return the process tomography target"""

qiskit_experiments/library/tomography/qst_experiment.py

@@ -59,6 +59,7 @@ def __init__(
         basis_indices: Optional[Sequence[List[int]]] = None,
         qubits: Optional[Sequence[int]] = None,
         analysis: Union[BaseAnalysis, None, str] = "default",
+        target: Union[Statevector, DensityMatrix, None, str] = "default",
     ):
         """Initialize a quantum process tomography experiment.
 
@@ -82,6 +83,10 @@ def __init__(
             analysis: Optional, a custom analysis instance to use. If ``"default"``
                 :class:`~.StateTomographyAnalysis` will be used. If None no analysis
                 instance will be set.
+            target: Optional, a custom quantum state target for computing the
+                state fidelity of the fitted density matrix during analysis.
+                If "default" the state will be inferred from the input circuit
+                if it contains no classical instructions.
         """
         if isinstance(circuit, Statevector):
             # Convert to circuit using initialize instruction
@@ -110,7 +115,9 @@ def __init__(
 
         # Set target quantum state
         if isinstance(self.analysis, TomographyAnalysis):
-            self.analysis.set_options(target=self._target_quantum_state())
+            if target == "default":
+                target = self._target_quantum_state()
+            self.analysis.set_options(target=target)
 
     def _target_quantum_state(self) -> Union[Statevector, DensityMatrix]:
         """Return the state tomography target"""

releasenotes/notes/tomo-kwargs-b091ce13d6983bc1.yaml → releasenotes/notes/tomography-b091ce13d6983bc1.yaml

@@ -1,11 +1,10 @@
 ---
 features:
   - |
-    Adds ``backend`` and ``analysis`` init kwargs to :class:`~.StateTomography`
-    and :class:`~.ProcessTomography` experiments to match the base
-    :class:`~.TomographyExperiment` init kwargs. This allows specifying the
-    intented backend, or a custom analysis class when initializing the
-    experiments.
+    Adds ``backend``, ``analysis``, and ``target`` init kwargs to the
+    :class:`~.StateTomography` and :class:`~.ProcessTomography` experiments.
+    These allow specifying intended backend, a custom analysis class, or a
+    custom target for fidelity calculations, when initializing the experiments.
 upgrade:
   - |
     Renames the ``qubits``, ``measurement_qubits``, and ``preparation_qubits``

test/library/tomography/test_process_tomography.py

@@ -24,6 +24,7 @@
 from qiskit_aer.noise import NoiseModel
 from qiskit_experiments.library import ProcessTomography, MitigatedProcessTomography
 from qiskit_experiments.library.tomography import ProcessTomographyAnalysis, basis
+from qiskit_experiments.database_service import ExperimentEntryNotFound
 from .tomo_utils import (
     FITTERS,
     filter_results,
@@ -477,3 +478,21 @@ def test_mitigated_full_qpt_random_unitary(self, qubits):
                     f_threshold,
                     msg=f"{fitter} fit fidelity is low for qubits {qubits}",
                 )
+
+    def test_target_none(self):
+        """Test setting target=None disables fidelity calculation."""
+        seed = 4343
+        backend = AerSimulator(seed_simulator=seed)
+        target = qi.random_unitary(2, seed=seed)
+        exp = ProcessTomography(target, backend=backend, target=None)
+        expdata = exp.run()
+        self.assertExperimentDone(expdata)
+        state = expdata.analysis_results("state").value
+        self.assertTrue(
+            isinstance(state, qi.Choi),
+            msg="Fitted state is not Choi matrix",
+        )
+        with self.assertRaises(
+            ExperimentEntryNotFound, msg="process_fidelity should not exist when target=None"
+        ):
+            expdata.analysis_results("process_fidelity")

test/library/tomography/test_state_tomography.py

@@ -26,6 +26,7 @@
 
 from qiskit_experiments.library import StateTomography, MitigatedStateTomography
 from qiskit_experiments.library.tomography import StateTomographyAnalysis, basis
+from qiskit_experiments.database_service import ExperimentEntryNotFound
 from .tomo_utils import (
     FITTERS,
     filter_results,
@@ -252,7 +253,7 @@ def test_experiment_config(self):
         self.assertTrue(self.json_equiv(exp, loaded_exp))
 
     def test_analysis_config(self):
-        """ "Test converting analysis to and from config works"""
+        """Test converting analysis to and from config works"""
         analysis = StateTomographyAnalysis()
         loaded = StateTomographyAnalysis.from_config(analysis.config())
         self.assertNotEqual(analysis, loaded)
@@ -375,3 +376,21 @@ def test_mitigated_full_qst(self, qubits):
                     f_threshold,
                     msg=f"{fitter} fit fidelity is low for qubits {qubits}",
                 )
+
+    def test_target_none(self):
+        """Test setting target=None disables fidelity calculation."""
+        seed = 4343
+        backend = AerSimulator(seed_simulator=seed)
+        target = qi.random_statevector(2, seed=seed)
+        exp = StateTomography(target, backend=backend, target=None)
+        expdata = exp.run()
+        self.assertExperimentDone(expdata)
+        state = expdata.analysis_results("state").value
+        self.assertTrue(
+            isinstance(state, qi.DensityMatrix),
+            msg="Fitted state is not density matrix",
+        )
+        with self.assertRaises(
+            ExperimentEntryNotFound, msg="state_fidelity should not exist when target=None"
+        ):
+            expdata.analysis_results("state_fidelity")