Merge branch 'Qiskit:main' into move-equivalence

qiskit/providers/fake_provider/generic_backend_v2.py

@@ -375,6 +375,11 @@ def _build_generic_target(self):
                     f"in the standard qiskit circuit library."
                 )
             gate = self._supported_gates[name]
+            if self.num_qubits < gate.num_qubits:
+                raise QiskitError(
+                    f"Provided basis gate {name} needs more qubits than {self.num_qubits}, "
+                    f"which is the size of the backend."
+                )
             noise_params = self._get_noise_defaults(name, gate.num_qubits)
             self._add_noisy_instruction_to_target(gate, noise_params, calibration_inst_map)
 

qiskit/synthesis/discrete_basis/generate_basis_approximations.py

@@ -156,7 +156,7 @@ def generate_basic_approximations(
         data = {}
         for sequence in sequences:
             gatestring = sequence.name
-            data[gatestring] = sequence.product
+            data[gatestring] = (sequence.product, sequence.global_phase)
 
         np.save(filename, data)
 

qiskit/synthesis/discrete_basis/solovay_kitaev.py

@@ -51,14 +51,19 @@ def __init__(
 
         self.basic_approximations = self.load_basic_approximations(basic_approximations)
 
-    def load_basic_approximations(self, data: list | str | dict) -> list[GateSequence]:
+    @staticmethod
+    def load_basic_approximations(data: list | str | dict) -> list[GateSequence]:
         """Load basic approximations.
 
         Args:
             data: If a string, specifies the path to the file from where to load the data.
-                If a dictionary, directly specifies the decompositions as ``{gates: matrix}``.
-                There ``gates`` are the names of the gates producing the SO(3) matrix ``matrix``,
-                e.g. ``{"h t": np.array([[0, 0.7071, -0.7071], [0, -0.7071, -0.7071], [-1, 0, 0]]}``.
+                If a dictionary, directly specifies the decompositions as ``{gates: matrix}``
+                or ``{gates: (matrix, global_phase)}``. There, ``gates`` are the names of the gates
+                producing the SO(3) matrix ``matrix``, e.g.
+                ``{"h t": np.array([[0, 0.7071, -0.7071], [0, -0.7071, -0.7071], [-1, 0, 0]]}``
+                and the ``global_phase`` can be given to account for a global phase difference
+                between the U(2) matrix of the quantum gates and the stored SO(3) matrix.
+                If not given, the ``global_phase`` will be assumed to be 0.
 
         Returns:
             A list of basic approximations as type ``GateSequence``.
@@ -72,13 +77,20 @@ def load_basic_approximations(self, data: list | str | dict) -> list[GateSequenc
 
         # if a file, load the dictionary
         if isinstance(data, str):
-            data = np.load(data, allow_pickle=True)
+            data = np.load(data, allow_pickle=True).item()
 
         sequences = []
-        for gatestring, matrix in data.items():
+        for gatestring, matrix_and_phase in data.items():
+            if isinstance(matrix_and_phase, tuple):
+                matrix, global_phase = matrix_and_phase
+            else:
+                matrix, global_phase = matrix_and_phase, 0
+
             sequence = GateSequence()
             sequence.gates = [_1q_gates[element] for element in gatestring.split()]
+            sequence.labels = [gate.name for gate in sequence.gates]
             sequence.product = np.asarray(matrix)
+            sequence.global_phase = global_phase
             sequences.append(sequence)
 
         return sequences

releasenotes/notes/fix-sk-load-from-file-02c6eabbbd7fcda3.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Fix the :class:`.SolovayKitaev` transpiler pass when loading basic
+    approximations from an exising ``.npy`` file. Previously, loading
+    a stored approximation which allowed for further reductions (e.g. due
+    to gate cancellations) could cause a runtime failure.
+    Additionally, the global phase difference of the U(2) gate product
+    and SO(3) representation was lost during a save-reload procedure.
+    Fixes `Qiskit/qiskit#12576 <https://github.com/Qiskit/qiskit/issues/12576>`_.

releasenotes/notes/fixes_GenericBackendV2-668e40596e1f070d.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    The constructor :class:`.GenericBackendV2` was allowing to create malformed backends because it accepted basis gates that couldn't be allocated in the backend size . That is, a backend with a single qubit should not accept a basis with two-qubit gates.

test/python/providers/fake_provider/test_generic_backend_v2.py

@@ -35,6 +35,16 @@ def test_supported_basis_gates(self):
         with self.assertRaises(QiskitError):
             GenericBackendV2(num_qubits=8, basis_gates=["cx", "id", "rz", "sx", "zz"])
 
+    def test_cx_1Q(self):
+        """Test failing with a backend with single qubit but with a two-qubit basis gate"""
+        with self.assertRaises(QiskitError):
+            GenericBackendV2(num_qubits=1, basis_gates=["cx", "id"])
+
+    def test_ccx_2Q(self):
+        """Test failing with a backend with two qubits but with a three-qubit basis gate"""
+        with self.assertRaises(QiskitError):
+            GenericBackendV2(num_qubits=2, basis_gates=["ccx", "id"])
+
     def test_operation_names(self):
         """Test that target basis gates include "delay", "measure" and "reset" even
         if not provided by user."""

test/python/transpiler/test_solovay_kitaev.py

@@ -12,8 +12,10 @@
 
 """Test the Solovay Kitaev transpilation pass."""
 
+import os
 import unittest
 import math
+import tempfile
 import numpy as np
 import scipy
 
@@ -230,6 +232,35 @@ def test_u_gates_work(self):
         included_gates = set(discretized.count_ops().keys())
         self.assertEqual(set(basis_gates), included_gates)
 
+    def test_load_from_file(self):
+        """Test loading basic approximations from a file works.
+
+        Regression test of Qiskit/qiskit#12576.
+        """
+        filename = "approximations.npy"
+
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            fullpath = os.path.join(tmp_dir, filename)
+
+            # dump approximations to file
+            generate_basic_approximations(basis_gates=["h", "s", "sdg"], depth=3, filename=fullpath)
+
+            # circuit to decompose and reference decomp
+            circuit = QuantumCircuit(1)
+            circuit.rx(0.8, 0)
+
+            reference = QuantumCircuit(1, global_phase=3 * np.pi / 4)
+            reference.h(0)
+            reference.s(0)
+            reference.h(0)
+
+            # load the decomp and compare to reference
+            skd = SolovayKitaev(basic_approximations=fullpath)
+            # skd = SolovayKitaev(basic_approximations=filename)
+            discretized = skd(circuit)
+
+        self.assertEqual(discretized, reference)
+
 
 @ddt
 class TestGateSequence(QiskitTestCase):

test/visual/mpl/graph/test_graph_matplotlib_drawer.py

@@ -389,7 +389,7 @@ def test_plot_1_qubit_gate_map(self):
         """Test plot_gate_map using 1 qubit backend"""
         # getting the mock backend from FakeProvider
 
-        backend = GenericBackendV2(num_qubits=1)
+        backend = GenericBackendV2(num_qubits=1, basis_gates=["id", "rz", "sx", "x"])
 
         fname = "1_qubit_gate_map.png"
         self.graph_plot_gate_map(backend=backend, filename=fname)