Merge remote-tracking branch 'upstream/main'

crates/accelerate/Cargo.toml

@@ -26,6 +26,7 @@ qiskit-circuit.workspace = true
 thiserror.workspace = true
 ndarray_einsum_beta = "0.7"
 once_cell = "1.20.2"
+bytemuck.workspace = true
 
 [dependencies.smallvec]
 workspace = true

crates/accelerate/src/lib.rs

@@ -40,6 +40,7 @@ pub mod remove_diagonal_gates_before_measure;
 pub mod results;
 pub mod sabre;
 pub mod sampled_exp_val;
+pub mod sparse_observable;
 pub mod sparse_pauli_op;
 pub mod split_2q_unitaries;
 pub mod star_prerouting;

crates/circuit/src/imports.rs

@@ -122,6 +122,8 @@ pub static XX_DECOMPOSER: ImportOnceCell =
     ImportOnceCell::new("qiskit.synthesis.two_qubit.xx_decompose", "XXDecomposer");
 pub static XX_EMBODIMENTS: ImportOnceCell =
     ImportOnceCell::new("qiskit.synthesis.two_qubit.xx_decompose", "XXEmbodiments");
+pub static NUMPY_COPY_ONLY_IF_NEEDED: ImportOnceCell =
+    ImportOnceCell::new("qiskit._numpy_compat", "COPY_ONLY_IF_NEEDED");
 
 /// A mapping from the enum variant in crate::operations::StandardGate to the python
 /// module path and class name to import it. This is used to populate the conversion table

crates/pyext/src/lib.rs

@@ -53,6 +53,7 @@ fn _accelerate(m: &Bound<PyModule>) -> PyResult<()> {
     add_submodule(m, ::qiskit_accelerate::results::results, "results")?;
     add_submodule(m, ::qiskit_accelerate::sabre::sabre, "sabre")?;
     add_submodule(m, ::qiskit_accelerate::sampled_exp_val::sampled_exp_val, "sampled_exp_val")?;
+    add_submodule(m, ::qiskit_accelerate::sparse_observable::sparse_observable, "sparse_observable")?;
     add_submodule(m, ::qiskit_accelerate::sparse_pauli_op::sparse_pauli_op, "sparse_pauli_op")?;
     add_submodule(m, ::qiskit_accelerate::split_2q_unitaries::split_2q_unitaries_mod, "split_2q_unitaries")?;
     add_submodule(m, ::qiskit_accelerate::star_prerouting::star_prerouting, "star_prerouting")?;

crates/qasm2/src/parse.rs

@@ -827,8 +827,16 @@ impl State {
         }
         bc.push(Some(InternalBytecode::EndDeclareGate {}));
         self.gate_symbols.clear();
-        self.define_gate(Some(&gate_token), name, num_params, num_qubits)?;
-        Ok(statements + 2)
+        let num_bytecode = statements + 2;
+        if self.define_gate(Some(&gate_token), name, num_params, num_qubits)? {
+            Ok(num_bytecode)
+        } else {
+            // The gate was built-in, so we don't actually need to emit the bytecode.  This is
+            // uncommon, so it doesn't matter too much that we throw away allocation work we did -
+            // it still helps that we verified that the gate body was valid OpenQASM 2.
+            bc.truncate(bc.len() - num_bytecode);
+            Ok(0)
+        }
     }
 
     /// Parse an `opaque` statement.  This assumes that the `opaque` token is still in the token
@@ -1634,6 +1642,9 @@ impl State {
     /// bytecode because not all gate definitions need something passing to Python.  For example,
     /// the Python parser initializes its state including the built-in gates `U` and `CX`, and
     /// handles the `qelib1.inc` include specially as well.
+    ///
+    /// Returns whether the gate needs to be defined in Python space (`true`) or if it was some sort
+    /// of built-in that doesn't need the definition (`false`).
     fn define_gate(
         &mut self,
         owner: Option<&Token>,
@@ -1685,12 +1696,14 @@ impl State {
             }
             match self.symbols.get(&name) {
                 None => {
+                    // The gate wasn't a built-in, so we need to move the symbol in, but we don't
+                    // need to increment the number of gates because it's already got a gate ID
+                    // assigned.
                     self.symbols.insert(name, symbol.into());
-                    self.num_gates += 1;
-                    Ok(true)
+                    Ok(false)
                 }
                 Some(GlobalSymbol::Gate { .. }) => {
-                    self.symbols.insert(name, symbol.into());
+                    // The gate was built-in and we can ignore the new definition (it's the same).
                     Ok(false)
                 }
                 _ => already_defined(self, name),

qiskit/__init__.py

@@ -79,6 +79,7 @@
 sys.modules["qiskit._accelerate.results"] = _accelerate.results
 sys.modules["qiskit._accelerate.sabre"] = _accelerate.sabre
 sys.modules["qiskit._accelerate.sampled_exp_val"] = _accelerate.sampled_exp_val
+sys.modules["qiskit._accelerate.sparse_observable"] = _accelerate.sparse_observable
 sys.modules["qiskit._accelerate.sparse_pauli_op"] = _accelerate.sparse_pauli_op
 sys.modules["qiskit._accelerate.star_prerouting"] = _accelerate.star_prerouting
 sys.modules["qiskit._accelerate.stochastic_swap"] = _accelerate.stochastic_swap

qiskit/quantum_info/__init__.py

@@ -28,6 +28,7 @@
    Pauli
    Clifford
    ScalarOp
+   SparseObservable
    SparsePauliOp
    CNOTDihedral
    PauliList
@@ -113,6 +114,9 @@
 """
 
 from __future__ import annotations
+
+from qiskit._accelerate.sparse_observable import SparseObservable
+
 from .analysis import hellinger_distance, hellinger_fidelity, Z2Symmetries
 from .operators import (
     Clifford,

releasenotes/notes/qasm2-builtin-gate-d80c2868cdf5f958.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    The OpenQASM 2 importer previously would output incorrect :class:`.Gate` instances for gate
+    calls referring to a ``gate`` definition that followed a prior ``gate`` definition that was
+    being treated as a built-in operation by a :class:`~.qasm2.CustomInstruction`.  See
+    `#13339 <https://github.com/Qiskit/qiskit/issues/13339>`__ for more detail.

releasenotes/notes/sparse-observable-7de70dcdf6962a64.yaml

@@ -0,0 +1,32 @@
+---
+features_quantum_info:
+  - |
+    A new observable class has been added.  :class:`.SparseObservable` represents observables as a
+    sum of terms, similar to :class:`.SparsePauliOp`, but with two core differences:
+
+    1. Each complete term is stored as (effectively) a series of ``(qubit, bit_term)`` pairs,
+       without storing qubits that undergo the identity for that term.  This significantly improves
+       the memory usage of observables such as the weighted sum of Paulis :math:`\sum_i c_i Z_i`.
+
+    2. The single-qubit term alphabet is overcomplete for the operator space; it can represent Pauli 
+       operators (like :class:`.SparsePauliOp`), but also projectors onto the eigenstates of the
+       Pauli operators, like :math:`\lvert 0\rangle\langle 0\rangle`.  Such projectors can be
+       measured on hardware equally as efficiently as their corresponding Pauli operator, but
+       :class:`.SparsePauliOp` would require an exponential number of terms to represent
+       :math:`{\lvert0\rangle\langle0\rvert}^{\otimes n}` over :math:`n` qubits, while
+       :class:`.SparseObservable` needs only a single term.
+
+    You can construct and manipulate :class:`.SparseObservable` using an interface familiar to users
+    of :class:`.SparsePauliOp`::
+
+      from qiskit.quantum_info import SparseObservable
+
+      obs = SparseObservable.from_sparse_list([
+        ("XZY", (2, 1, 0), 1.5j),
+        ("+-", (100, 99), 0.5j),
+        ("01", (50, 49), 0.5),
+      ])
+
+    :class:`.SparseObservable` is not currently supported as an input format to the primitives
+    (:mod:`qiskit.primitives`), but we expect to expand these interfaces to include them in the
+    future.

test/python/qasm2/test_structure.py

@@ -1648,6 +1648,47 @@ def __init__(self, a):
         qc.append(MyGate(0.5), [0])
         self.assertEqual(parsed, qc)
 
+    def test_compatible_definition_of_builtin_is_ignored(self):
+        program = """
+            qreg q[1];
+            gate my_gate a { U(0, 0, 0) a; }
+            my_gate q[0];
+        """
+
+        class MyGate(Gate):
+            def __init__(self):
+                super().__init__("my_gate", 1, [])
+
+            def _define(self):
+                self._definition = QuantumCircuit(1)
+                self._definition.z(0)
+
+        parsed = qiskit.qasm2.loads(
+            program, custom_instructions=[qiskit.qasm2.CustomInstruction("my_gate", 0, 1, MyGate)]
+        )
+        self.assertEqual(parsed.data[0].operation.definition, MyGate().definition)
+
+    def test_gates_defined_after_a_builtin_align(self):
+        """It's easy to get out of sync between the Rust-space and Python-space components when
+        ``builtin=True``. See https://github.com/Qiskit/qiskit/issues/13339."""
+        program = """
+        OPENQASM 2.0;
+        gate first a { U(0, 0, 0) a; }
+        gate second a { U(pi, pi, pi) a; }
+
+        qreg q[1];
+        first q[0];
+        second q[0];
+        """
+        custom = qiskit.qasm2.CustomInstruction("first", 0, 1, lib.XGate, builtin=True)
+        parsed = qiskit.qasm2.loads(program, custom_instructions=[custom])
+        # Provided definitions for built-in gates are ignored, so it should be an XGate directly.
+        self.assertEqual(parsed.data[0].operation, lib.XGate())
+        self.assertEqual(parsed.data[1].operation.name, "second")
+        defn = parsed.data[1].operation.definition.copy_empty_like()
+        defn.u(math.pi, math.pi, math.pi, 0)
+        self.assertEqual(parsed.data[1].operation.definition, defn)
+
 
 class TestCustomClassical(QiskitTestCase):
     def test_qiskit_extensions(self):