Add qiskit -> ProjectQ parser using qiskit

Author: Takishima

projectq/libs/qasm/__init__.py

@@ -0,0 +1,37 @@
+#   Copyright 2020 ProjectQ-Framework (www.projectq.ch)
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+"""
+Contains functions/classes to handle OpenQASM
+"""
+
+try:
+    from ._parse_qasm_qiskit import read_qasm_file, read_qasm_str
+except ImportError:  # pragma: no cover
+    import warnings
+
+    err = ('Unable to import qiskit\n'
+           'Please install it (e.g. using the command: '
+           'python -m pip install qiskit')
+
+    warnings.warn(err + 'c\n'
+                  'The provided read_qasm_* functions will systematically'
+                  'raise a RuntimeError')
+
+    def read_qasm_file(eng, filename):
+        # pylint: disable=unused-argument
+        raise RuntimeError(err)
+
+    def read_qasm_str(eng, qasm_str):
+        # pylint: disable=unused-argument
+        raise RuntimeError(err)

projectq/libs/qasm/_parse_qasm_qiskit.py

@@ -0,0 +1,173 @@
+#   Copyright 2020 ProjectQ-Framework (www.projectq.ch)
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+""" Define function to read OpenQASM file format (using Qiskit). """
+
+from projectq.ops import All, Measure, ControlledGate, SwapGate
+
+from qiskit.circuit import QuantumCircuit
+
+from ._qiskit_conv import gates_conv_table
+
+# ==============================================================================
+
+
+def apply_gate(gate, qubits):
+    """
+    Apply a gate to some qubits while separating control and target qubits.
+
+
+    Args:
+        gate (BasicGate): Instance of a ProjectQ gate
+        qubits (list): List of ProjectQ qubits the gate applies to.
+    """
+    if isinstance(gate, ControlledGate):
+        ctrls = qubits[:gate._n]
+        qubits = qubits[gate._n:]
+        if isinstance(gate._gate, SwapGate):
+            assert len(qubits) == 2
+            gate | (ctrls, qubits[0], qubits[1])
+        else:
+            gate | (ctrls, qubits)
+    elif isinstance(gate, SwapGate):
+        assert len(qubits) == 2
+        gate | (qubits[0], qubits[1])
+    else:
+        gate | qubits
+
+
+def apply_op(eng, gate, qubits, bits, bits_map):
+    """
+    Apply a qiskit operation.
+
+    This function takes care of converting between qiskit gates and ProjectQ
+    gates, as well as handling the translation between qiskit's and ProjectQ's
+    qubit and bits.
+
+    Args:
+        eng (MainEngine): MainEngine to use to the operation(s)
+        gate (qiskit.Gate): Qiskit gate to apply
+        qubits (list): List of ProjectQ qubits to apply the gate to
+        bits (list): List of classical bits to apply the gate to
+    """
+
+    if bits:
+        # Only measurement gates have clasical bits
+        assert len(qubits) == len(bits)
+        All(Measure) | qubits
+        eng.flush()
+
+        for idx, bit in enumerate(bits):
+            bits_map[bit.register.name][idx] = bool(qubits[idx])
+    else:
+        if gate.name not in gates_conv_table:
+            if not gate._definition:
+                return
+
+            gate_args = {gate._definition.qregs[0].name: qubits}
+
+            for gate_sub, quregs_sub, bits_sub in gate._definition.data:
+                # OpenQASM 2.0 limitation...
+                assert gate.name != 'measure' and not bits_sub
+                apply_op(eng, gate_sub, [
+                    gate_args[qubit.register.name][qubit.index]
+                    for qubit in quregs_sub
+                ], [], bits_map)
+        else:
+            if gate.params:
+                gate_projectq = gates_conv_table[gate.name](*gate.params)
+            else:
+                gate_projectq = gates_conv_table[gate.name]
+
+            if gate.condition:
+                # OpenQASM 2.0
+                cbit, value = gate.condition
+
+                # Note: apparently, it is illegal to write if (c0[0] == 1)
+                #      so we always assume that index == 0...
+                if bits_map[cbit.name][0] == value:
+                    apply_gate(gate_projectq, qubits)
+            else:
+                apply_gate(gate_projectq, qubits)
+
+
+def _convert_qiskit_circuit(eng, qc):
+    """
+    Convert a QisKit circuit and convert it to ProjectQ commands.
+
+    This function supports OpenQASM 2.0 (3.0 is experimental)
+
+    Args:
+        eng (MainEngine): MainEngine to use for creating qubits and commands.
+        qc (qiskit.QuantumCircuit): Quantum circuit to process
+
+    Note:
+        At this time, we support most of OpenQASM 2.0 and some of 3.0,
+        although the latter is still experimental.
+    """
+    # Create maps between qiskit and ProjectQ for qubits and bits
+    qubits_map = {
+        qureg.name: eng.allocate_qureg(qureg.size)
+        for qureg in qc.qregs
+    }
+    bits_map = {bit.name: [None] * bit.size for bit in qc.cregs}
+
+    # Convert all the gates to ProjectQ commands
+    for gate, quregs, bits in qc.data:
+        apply_op(
+            eng, gate,
+            [qubits_map[qubit.register.name][qubit.index]
+             for qubit in quregs], bits, bits_map)
+
+    return qubits_map, bits_map
+
+def read_qasm_str(eng, qasm_str):
+    """
+    Read an OpenQASM (2.0, 3.0 is experimental) string and convert it to
+    ProjectQ commands.
+
+    This version of the function uses Qiskit in order to parse the *.qasm
+    file.
+
+    Args:
+        eng (MainEngine): MainEngine to use for creating qubits and commands.
+        filename (string): Path to *.qasm file
+
+    Note:
+        At this time, we support most of OpenQASM 2.0 and some of 3.0,
+        although the latter is still experimental.
+    """
+    qc = QuantumCircuit.from_qasm_str(qasm_str)
+    return _convert_qiskit_circuit(eng, qc)
+
+
+def read_qasm_file(eng, filename):
+    """
+    Read an OpenQASM (2.0, 3.0 is experimental) file and convert it to
+    ProjectQ commands.
+
+    This version of the function uses Qiskit in order to parse the *.qasm
+    file.
+
+    Args:
+        eng (MainEngine): MainEngine to use for creating qubits and commands.
+        filename (string): Path to *.qasm file
+
+    Note:
+        At this time, we support most of OpenQASM 2.0 and some of 3.0,
+        although the latter is still experimental.
+    """
+
+    qc = QuantumCircuit.from_qasm_file(filename)
+
+    return _convert_qiskit_circuit(eng, qc)