Assuming 1q and 2q gates in QPU.expval (#36)

pennylane_forest/qpu.py

@@ -130,9 +130,15 @@ def expval(self, observable, wires, par):
                 prep_prog = Program()
                 for instr in self.program.instructions:
                     if isinstance(instr, Gate):
-                        # assumes single qubit gates
-                        gate, _ = instr.out().split(' ')
-                        prep_prog += Program(str(gate) + ' ' + str(qubit))
+                        # split gate and wires -- assumes 1q and 2q gates
+                        tup_gate_wires = instr.out().split(' ')
+                        gate = tup_gate_wires[0]
+                        str_instr = str(gate)
+                        # map wires to qubits
+                        for w in tup_gate_wires[1:]:
+                            str_instr += f' {self.wiring[int(w)]}'
+                        prep_prog += Program(str_instr)
+
                 if self.readout_error is not None:
                     prep_prog.define_noisy_readout(qubit, p00=self.readout_error[0],
                                                           p11=self.readout_error[1])

tests/test_qpu.py

@@ -150,3 +150,16 @@ def circuit_Zmi():
 
         assert np.allclose(results[:3], 1.0, atol=2e-2)
         assert np.allclose(results[3:], -1.0, atol=2e-2)
+
+    def test_2q_gate(self):
+        device = np.random.choice(VALID_QPU_LATTICES)
+        dev_qpu = qml.device('forest.qpu', device=device, load_qc=False, readout_error=[0.9, 0.75],
+                            symmetrize_readout="exhaustive", calibrate_readout="plus-eig")
+
+        @qml.qnode(dev_qpu)
+        def circuit():
+            qml.RY(np.pi/2, wires=[0])
+            qml.CNOT(wires=[0, 1])
+            return qml.expval(qml.PauliZ(0))
+
+        assert np.allclose(circuit(), 0.0, atol=2e-2)