Initial outline of paper2 circuit ansatz

examples/psr_paper2.py

@@ -19,10 +19,9 @@
 from qibo.optimizers import optimize
 from scipy.optimize import minimize
 
-from qibochem.ansatz.hf_reference import hf_circuit
-from qibochem.ansatz.ucc import ucc_circuit
-from qibochem.driver.molecule import Molecule
-from qibochem.measurement.expectation import expectation
+from qibochem.ansatz import hf_circuit, ucc_circuit
+from qibochem.driver import Molecule
+from qibochem.measurement import expectation
 
 # mol = Molecule(xyz_file="h2.xyz")
 h2 = Molecule([("Li", (0.0, 0.0, 0.0)), ("H", (0.0, 0.0, 1.4))])
@@ -75,6 +74,9 @@ def A_gate(a):
     Xpositions += [2 * j + 1 for j in range(h2.n_active_e - math.ceil(h2.n_active_orbs / 2))]
     Xpositions.sort()
 
+print(Xpositions)
+quit()
+
 
 # setting the circuit up
 def setup_electrons(g2):

src/qibochem/ansatz/symmetry.py

@@ -0,0 +1,52 @@
+"""
+Symmetry-Preserving circuit ansatz from Gard et al. Reference: https://doi.org/10.1038/s41534-019-0240-1
+"""
+
+import numpy as np
+from qibo import Circuit, gates
+
+# Helper functions
+
+
+def a_gate(qubit1, qubit2):
+    """
+    Returns the list of elementary gates corresponding to the 'A' gate as defined in the paper, acting on qubit1 and qubit2
+    """
+    result = []
+    result.append(gates.CNOT(qubit2, qubit1))
+    result += [gates.RY(qubit2, 0.0), gates.RZ(qubit2, 0.0)]
+    result.append(gates.CNOT(qubit1, qubit2))
+    result += [gates.RZ(qubit2, 0.0), gates.RY(qubit2, 0.0)]
+    result.append(gates.CNOT(qubit2, qubit1))
+    return result
+
+
+# Main function
+def symm_preserving_circuit(n_qubits, n_electrons):
+    """
+    Symmetry-preserving circuit ansatz
+
+    Args:
+        n_qubits: Number of qubits in the quantum circuit
+        n_electrons: Number of electrons in the molecular system
+
+    Returns:
+        Qibo ``Circuit``: Circuit ansatz
+    """
+    circuit = Circuit(n_qubits)
+    circuit.add(gates.X(2 * _i) for _i in range(n_electrons))
+
+    a_gate_qubits = []  # Generate the list of qubits pairs for adding A gates
+
+    a_gate_qubits = [(0, 1)]
+
+    a_gates = [a_gate(qubit1, qubit2) for qubit1, qubit2 in a_gate_qubits]
+    circuit.add(_gates for _a_gate in a_gates for _gates in _a_gate)  # Unpack the nested list
+
+    return circuit
+
+
+n_qubits = 4
+n_electrons = 2
+circuit = symm_preserving_circuit(n_qubits, n_electrons)
+print(circuit.draw())