Make the cutting workflow work with any Hashable as label

circuit_knitting/cutting/cutting_decomposition.py

@@ -34,9 +34,9 @@
 class PartitionedCuttingProblem(NamedTuple):
     """The result of decomposing and separating a circuit and observable(s)."""
 
-    subcircuits: dict[str | int, QuantumCircuit]
+    subcircuits: dict[Hashable, QuantumCircuit]
     bases: list[QPDBasis]
-    subobservables: dict[str | int, PauliList] | None = None
+    subobservables: dict[Hashable, PauliList] | None = None
 
 
 def partition_circuit_qubits(
@@ -162,7 +162,7 @@ def cut_gates(
 
 def partition_problem(
     circuit: QuantumCircuit,
-    partition_labels: Sequence[str | int] | None = None,
+    partition_labels: Sequence[Hashable] | None = None,
     observables: PauliList | None = None,
 ) -> PartitionedCuttingProblem:
     r"""
@@ -258,8 +258,8 @@ def partition_problem(
 
 
 def decompose_observables(
-    observables: PauliList, partition_labels: Sequence[str | int]
-) -> dict[str | int, PauliList]:
+    observables: PauliList, partition_labels: Sequence[Hashable]
+) -> dict[Hashable, PauliList]:
     """
     Decompose a list of observables with respect to some qubit partition labels.
 

circuit_knitting/cutting/cutting_evaluation.py

@@ -14,7 +14,7 @@
 from __future__ import annotations
 
 from typing import NamedTuple
-from collections.abc import Sequence
+from collections.abc import Sequence, Hashable
 
 from qiskit.circuit import QuantumCircuit
 from qiskit.quantum_info import PauliList
@@ -28,15 +28,15 @@
 class CuttingExperimentResults(NamedTuple):
     """Circuit cutting subexperiment results and sampling coefficients."""
 
-    results: SamplerResult | dict[str | int, SamplerResult]
+    results: SamplerResult | dict[Hashable, SamplerResult]
     coeffs: Sequence[tuple[float, WeightType]]
 
 
 def execute_experiments(
-    circuits: QuantumCircuit | dict[str | int, QuantumCircuit],
-    subobservables: PauliList | dict[str | int, PauliList],
+    circuits: QuantumCircuit | dict[Hashable, QuantumCircuit],
+    subobservables: PauliList | dict[Hashable, PauliList],
     num_samples: int,
-    samplers: BaseSampler | dict[str | int, BaseSampler],
+    samplers: BaseSampler | dict[Hashable, BaseSampler],
 ) -> CuttingExperimentResults:
     r"""
     Generate the sampled circuits, append the observables, and run the sub-experiments.
@@ -90,7 +90,7 @@ def execute_experiments(
 
     if isinstance(samplers, dict):
         # Ensure that each sampler is unique
-        collision_dict: dict[int, str | int] = {}
+        collision_dict: dict[int, Hashable] = {}
         for k, v in samplers.items():
             if id(v) in collision_dict:
                 raise ValueError(
@@ -109,7 +109,7 @@ def execute_experiments(
     )
 
     # Set up subexperiments and samplers
-    subexperiments_dict: dict[str | int, list[QuantumCircuit]] = {}
+    subexperiments_dict: dict[Hashable, list[QuantumCircuit]] = {}
     if isinstance(subexperiments, list):
         subexperiments_dict = {"A": subexperiments}
     else:
@@ -124,7 +124,7 @@ def execute_experiments(
     # Make sure the first two cregs in each circuit are for QPD and observable measurements
     # Run a job for each partition and collect results
     results = {}
-    for label in sorted(subexperiments_dict.keys()):
+    for label in subexperiments_dict.keys():
         for circ in subexperiments_dict[label]:
             if (
                 len(circ.cregs) != 2
@@ -152,7 +152,7 @@ def execute_experiments(
     return CuttingExperimentResults(results=results_out, coeffs=coefficients)
 
 
-def _validate_samplers(samplers: BaseSampler | dict[str | int, BaseSampler]) -> None:
+def _validate_samplers(samplers: BaseSampler | dict[Hashable, BaseSampler]) -> None:
     """Replace unsupported statevector-based Samplers with ExactSampler."""
     if isinstance(samplers, BaseSampler):
         if (

circuit_knitting/cutting/cutting_experiments.py

@@ -14,7 +14,7 @@
 from __future__ import annotations
 
 from collections import defaultdict
-from collections.abc import Sequence
+from collections.abc import Sequence, Hashable
 
 import numpy as np
 from qiskit.circuit import QuantumCircuit, ClassicalRegister
@@ -34,11 +34,11 @@
 
 
 def generate_cutting_experiments(
-    circuits: QuantumCircuit | dict[str | int, QuantumCircuit],
-    observables: PauliList | dict[str | int, PauliList],
+    circuits: QuantumCircuit | dict[Hashable, QuantumCircuit],
+    observables: PauliList | dict[Hashable, PauliList],
     num_samples: int | float,
 ) -> tuple[
-    list[QuantumCircuit] | dict[str | int, list[QuantumCircuit]],
+    list[QuantumCircuit] | dict[Hashable, list[QuantumCircuit]],
     list[tuple[float, WeightType]],
 ]:
     r"""
@@ -98,7 +98,7 @@ def generate_cutting_experiments(
     # can be shared between both cases.
     if isinstance(circuits, QuantumCircuit):
         is_separated = False
-        subcircuit_list = [circuits]
+        subcircuit_dict: dict[Hashable, QuantumCircuit] = {"A": circuits}
         subobservables_by_subsystem = decompose_observables(
             observables, "A" * len(observables[0])
         )
@@ -108,16 +108,16 @@ def generate_cutting_experiments(
         }
         # Gather the unique bases from the circuit
         bases, qpd_gate_ids = _get_bases(circuits)
-        subcirc_qpd_gate_ids = [qpd_gate_ids]
+        subcirc_qpd_gate_ids: dict[Hashable, list[list[int]]] = {"A": qpd_gate_ids}
 
     else:
         is_separated = True
-        subcircuit_list = [circuits[key] for key in sorted(circuits.keys())]
+        subcircuit_dict = circuits
         # Gather the unique bases across the subcircuits
         subcirc_qpd_gate_ids, subcirc_map_ids = _get_mapping_ids_by_partition(
-            subcircuit_list
+            subcircuit_dict
         )
-        bases = _get_bases_by_partition(subcircuit_list, subcirc_qpd_gate_ids)
+        bases = _get_bases_by_partition(subcircuit_dict, subcirc_qpd_gate_ids)
 
         # Create the commuting observable groups
         subsystem_observables = {
@@ -135,7 +135,7 @@ def generate_cutting_experiments(
     sorted_samples = sorted(random_samples.items(), key=lambda x: x[1][0], reverse=True)
 
     # Generate the output experiments and their respective coefficients
-    subexperiments_dict: dict[str | int, list[QuantumCircuit]] = defaultdict(list)
+    subexperiments_dict: dict[Hashable, list[QuantumCircuit]] = defaultdict(list)
     coefficients: list[tuple[float, WeightType]] = []
     for z, (map_ids, (redundancy, weight_type)) in enumerate(sorted_samples):
         actual_coeff = np.prod(
@@ -144,22 +144,20 @@ def generate_cutting_experiments(
         sampled_coeff = (redundancy / num_samples) * (kappa * np.sign(actual_coeff))
         coefficients.append((sampled_coeff, weight_type))
         map_ids_tmp = map_ids
-        for i, (subcircuit, label) in enumerate(
-            strict_zip(subcircuit_list, sorted(subsystem_observables.keys()))
-        ):
+        for label, so in subsystem_observables.items():
+            subcircuit = subcircuit_dict[label]
             if is_separated:
-                map_ids_tmp = tuple(map_ids[j] for j in subcirc_map_ids[i])
+                map_ids_tmp = tuple(map_ids[j] for j in subcirc_map_ids[label])
             decomp_qc = decompose_qpd_instructions(
-                subcircuit, subcirc_qpd_gate_ids[i], map_ids_tmp
+                subcircuit, subcirc_qpd_gate_ids[label], map_ids_tmp
             )
-            so = subsystem_observables[label]
             for j, cog in enumerate(so.groups):
                 meas_qc = _append_measurement_circuit(decomp_qc, cog)
                 subexperiments_dict[label].append(meas_qc)
 
     # If the input was a single quantum circuit, return the subexperiments as a list
     subexperiments_out: list[QuantumCircuit] | dict[
-        str | int, list[QuantumCircuit]
+        Hashable, list[QuantumCircuit]
     ] = dict(subexperiments_dict)
     assert isinstance(subexperiments_out, dict)
     if isinstance(circuits, QuantumCircuit):
@@ -170,16 +168,16 @@ def generate_cutting_experiments(
 
 
 def _get_mapping_ids_by_partition(
-    circuits: Sequence[QuantumCircuit],
-) -> tuple[list[list[list[int]]], list[list[int]]]:
+    circuits: dict[Hashable, QuantumCircuit],
+) -> tuple[dict[Hashable, list[list[int]]], dict[Hashable, list[int]]]:
     """Get indices to the QPD gates in each subcircuit and relevant map ids."""
     # Collect QPDGate id's and relevant map id's for each subcircuit
-    subcirc_qpd_gate_ids: list[list[list[int]]] = []
-    subcirc_map_ids: list[list[int]] = []
+    subcirc_qpd_gate_ids: dict[Hashable, list[list[int]]] = {}
+    subcirc_map_ids: dict[Hashable, list[int]] = {}
     decomp_ids = set()
-    for circ in circuits:
-        subcirc_qpd_gate_ids.append([])
-        subcirc_map_ids.append([])
+    for label, circ in circuits.items():
+        subcirc_qpd_gate_ids[label] = []
+        subcirc_map_ids[label] = []
         for i, inst in enumerate(circ.data):
             if isinstance(inst.operation, SingleQubitQPDGate):
                 try:
@@ -194,24 +192,24 @@ def _get_mapping_ids_by_partition(
                         "belonging to the same cut to be sampled jointly."
                     )
                 decomp_ids.add(decomp_id)
-                subcirc_qpd_gate_ids[-1].append([i])
-                subcirc_map_ids[-1].append(decomp_id)
+                subcirc_qpd_gate_ids[label].append([i])
+                subcirc_map_ids[label].append(decomp_id)
 
     return subcirc_qpd_gate_ids, subcirc_map_ids
 
 
 def _get_bases_by_partition(
-    circuits: Sequence[QuantumCircuit], subcirc_qpd_gate_ids: list[list[list[int]]]
+    circuits: dict[Hashable, QuantumCircuit],
+    subcirc_qpd_gate_ids: dict[Hashable, list[list[int]]],
 ) -> list[QPDBasis]:
     """Get a list of each unique QPD basis across the subcircuits."""
     # Collect the bases corresponding to each decomposed operation
     bases_dict = {}
-    for i, subcirc in enumerate(subcirc_qpd_gate_ids):
+    for label, subcirc in subcirc_qpd_gate_ids.items():
+        circuit = circuits[label]
         for basis_id in subcirc:
-            decomp_id = int(
-                circuits[i].data[basis_id[0]].operation.label.split("_")[-1]
-            )
-            bases_dict[decomp_id] = circuits[i].data[basis_id[0]].operation.basis
+            decomp_id = int(circuit.data[basis_id[0]].operation.label.split("_")[-1])
+            bases_dict[decomp_id] = circuit.data[basis_id[0]].operation.basis
     bases = [bases_dict[key] for key in sorted(bases_dict.keys())]
 
     return bases

circuit_knitting/cutting/cutting_reconstruction.py

@@ -13,7 +13,7 @@
 
 from __future__ import annotations
 
-from collections.abc import Sequence
+from collections.abc import Sequence, Hashable
 
 import numpy as np
 from qiskit.quantum_info import PauliList
@@ -26,9 +26,9 @@
 
 
 def reconstruct_expectation_values(
-    results: SamplerResult | dict[str | int, SamplerResult],
+    results: SamplerResult | dict[Hashable, SamplerResult],
     coefficients: Sequence[tuple[float, WeightType]],
-    observables: PauliList | dict[str | int, PauliList],
+    observables: PauliList | dict[Hashable, PauliList],
 ) -> list[float]:
     r"""
     Reconstruct an expectation value from the results of the sub-experiments.
@@ -85,7 +85,7 @@ def reconstruct_expectation_values(
         subobservables_by_subsystem = decompose_observables(
             observables, "A" * len(observables[0])
         )
-        results_dict: dict[str | int, SamplerResult] = {"A": results}
+        results_dict: dict[Hashable, SamplerResult] = {"A": results}
         expvals = np.zeros(len(observables))
 
     else:
@@ -100,13 +100,11 @@ def reconstruct_expectation_values(
         label: ObservableCollection(subobservables)
         for label, subobservables in subobservables_by_subsystem.items()
     }
-    sorted_subsystems = sorted(subsystem_observables.keys())
 
     # Reconstruct the expectation values
     for i, coeff in enumerate(coefficients):
         current_expvals = np.ones((len(expvals),))
-        for label in sorted_subsystems:
-            so = subsystem_observables[label]
+        for label, so in subsystem_observables.items():
             subsystem_expvals = [
                 np.zeros(len(cog.commuting_observables)) for cog in so.groups
             ]

test/cutting/test_cutting_workflows.py

@@ -11,16 +11,22 @@
 
 """Tests of various cutting workflows, particularly with regard to flexibility in transpilation."""
 
+import pytest
 from copy import deepcopy
 
 from qiskit.circuit.library import EfficientSU2, CXGate
 from qiskit.quantum_info import PauliList
 from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
 from qiskit.providers.fake_provider import FakeLagosV2
+from qiskit_aer.primitives import Sampler
 
 from circuit_knitting.cutting.qpd.instructions import SingleQubitQPDGate
 from circuit_knitting.cutting.qpd import QPDBasis
-from circuit_knitting.cutting import partition_problem
+from circuit_knitting.cutting import (
+    partition_problem,
+    generate_cutting_experiments,
+    reconstruct_expectation_values,
+)
 
 
 def test_transpile_before_realizing_basis_id():
@@ -48,3 +54,48 @@ def test_transpile_before_realizing_basis_id():
         label: pass_manager.run(subcircuits["A"])
         for label, circuit in subcircuits.items()
     }
+
+
+@pytest.mark.parametrize(
+    "label1,label2",
+    [
+        ("foo", frozenset({1, 2, 4})),
+        (42, "bar"),
+    ],
+)
+def test_exotic_labels(label1, label2):
+    """Test workflow with labels of non-uniform type."""
+    circuit = EfficientSU2(4, entanglement="linear", reps=2).decompose()
+    circuit.assign_parameters([0.8] * len(circuit.parameters), inplace=True)
+    observables = PauliList(["ZZII", "IZZI", "IIZZ", "XIXI", "ZIZZ", "IXIX"])
+    subcircuits, bases, subobservables = partition_problem(
+        circuit=circuit,
+        partition_labels=[label1, label1, label2, label2],
+        observables=observables,
+    )
+    assert set(subcircuits.keys()) == {label1, label2}
+
+    subexperiments, coefficients = generate_cutting_experiments(
+        subcircuits, subobservables, num_samples=1500
+    )
+    assert subexperiments.keys() == subcircuits.keys()
+
+    samplers = {
+        label1: Sampler(run_options={"shots": 10}),
+        label2: Sampler(run_options={"shots": 10}),
+    }
+    results = {
+        label: sampler.run(subexperiments[label]).result()
+        for label, sampler in samplers.items()
+    }
+
+    for label in results:
+        for i, subexperiment in enumerate(subexperiments[label]):
+            results[label].metadata[i]["num_qpd_bits"] = len(subexperiment.cregs[0])
+
+    simulated_expvals = reconstruct_expectation_values(
+        results,
+        coefficients,
+        subobservables,
+    )
+    assert len(simulated_expvals) == len(observables)