Fix circuit generation of 3Q+ InterleavedRB (#1015)

* Add tests for RB circuit generation Add tests for RB circuit generation add doc * Fix a bug in 3q+ interleaved RB circuit generation * Update comments Co-authored-by: Christopher J. Wood <[email protected]>
qiskit-community · Jan 23, 2023 · 0df9dbb · 0df9dbb
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Showing 3 changed files with 33 additions and 4 deletions.
diff --git a/qiskit_experiments/library/randomized_benchmarking/interleaved_rb_experiment.py b/qiskit_experiments/library/randomized_benchmarking/interleaved_rb_experiment.py
@@ -145,8 +145,9 @@ def __init__(
             self._interleaved_cliff = num_from_1q_circuit(interleaved_clifford.to_circuit())
         elif self.num_qubits == 2:
             self._interleaved_cliff = num_from_2q_circuit(interleaved_clifford.to_circuit())
+        # Convert interleaved element to circuit for speed in 3Q or more case
         else:
-            self._interleaved_cliff = interleaved_clifford
+            self._interleaved_cliff = interleaved_clifford.to_circuit()
         self._interleaved_element = interleaved_element  # Original interleaved element
         self._interleaved_op = None  # Transpiled interleaved element for speed
         self.analysis = InterleavedRBAnalysis()

diff --git a/qiskit_experiments/library/randomized_benchmarking/rb_experiment.py b/qiskit_experiments/library/randomized_benchmarking/rb_experiment.py
@@ -290,7 +290,6 @@ def __sample_sequence(self, length: int, rng: Generator) -> Sequence[SequenceEle
         if self.num_qubits == 2:
             return rng.integers(CliffordUtils.NUM_CLIFFORD_2_QUBIT, size=length)
         # Return circuit object instead of Clifford object for 3 or more qubits case for speed
-        # TODO: Revisit after terra#7269, #7483, #8585
         return [random_clifford(self.num_qubits, rng).to_circuit() for _ in range(length)]
 
     def _to_instruction(
@@ -318,7 +317,6 @@ def __compose_clifford_seq(
                 compose_1q if self.num_qubits == 1 else compose_2q, elements, base_elem
             )
         # 3 or more qubits: compose Clifford from circuits for speed
-        # TODO: Revisit after terra#7269, #7483, #8585
         circ = QuantumCircuit(self.num_qubits)
         for elem in elements:
             circ.compose(elem, inplace=True)

diff --git a/test/library/randomized_benchmarking/test_randomized_benchmarking.py b/test/library/randomized_benchmarking/test_randomized_benchmarking.py
@@ -18,7 +18,7 @@
 import numpy as np
 from ddt import ddt, data, unpack
 
-from qiskit.circuit import Delay, QuantumCircuit, Parameter
+from qiskit.circuit import Delay, QuantumCircuit, Parameter, Gate
 from qiskit.circuit.library import SXGate, CXGate, TGate, CZGate
 from qiskit.exceptions import QiskitError
 from qiskit.providers.fake_provider import FakeManila, FakeManilaV2, FakeWashington
@@ -84,6 +84,14 @@ def test_analysis_config(self):
         self.assertEqual(analysis.config(), loaded.config())
 
     # ### Tests for circuit generation ###
+    @data([[3], 4], [[4, 7], 5], [[0, 1, 2], 3])
+    @unpack
+    def test_generate_circuits(self, qubits, length):
+        """Test RB circuit generation"""
+        exp = rb.StandardRB(qubits=qubits, lengths=[length], num_samples=1)
+        circuits = exp.circuits()
+        self.assertAllIdentity(circuits)
+
     def test_return_same_circuit(self):
         """Test if setting the same seed returns the same circuits."""
         exp1 = rb.StandardRB(
@@ -265,6 +273,28 @@ def test_analysis_config(self):
         self.assertEqual(analysis.config(), loaded.config())
 
     # ### Tests for circuit generation ###
+    class ThreeQubitGate(Gate):
+        """A 3-qubit Clifford gate for tests"""
+
+        def __init__(self):
+            super().__init__("3q-gate", 3, [])
+
+        def _define(self):
+            qc = QuantumCircuit(3, name=self.name)
+            qc.cx(0, 1)
+            qc.x(2)
+            self.definition = qc
+
+    @data([SXGate(), [3], 4], [CXGate(), [4, 7], 5], [ThreeQubitGate(), [0, 1, 2], 3])
+    @unpack
+    def test_generate_interleaved_circuits(self, interleaved_element, qubits, length):
+        """Test interleaved circuit generation"""
+        exp = rb.InterleavedRB(
+            interleaved_element=interleaved_element, qubits=qubits, lengths=[length], num_samples=1
+        )
+        circuits = exp.circuits()
+        self.assertAllIdentity(circuits)
+
     @data([SXGate(), [3], 4], [CXGate(), [4, 7], 5])
     @unpack
     def test_interleaved_structure(self, interleaved_element, qubits, length):