added feb.py

src/qibochem/ansatz/feb.py

@@ -0,0 +1,98 @@
+import numpy as np 
+import qibo
+from qibo import Circuit, models, gates
+
+def MCRY(controls, target, parameter, trainable=True) -> Circuit:
+    """
+    multi-controlled RY gate
+    """
+    gate_list = []
+
+    if len(controls) > 2:
+        gate_list.append(gates.CRY(controls[-1], target, parameter/2.0, trainable=trainable))        
+        gate_list.append(gates.CRY(controls[-1], target, parameter/2.0, trainable=trainable))
+        gate_list.append(gates.X(controls[-1]).controlled_by(*controls[0:(len(controls)-1)]))
+        gate_list.append(gates.CRY(controls[-1], target, -parameter/2.0, trainable=trainable))
+        gate_list.append(gates.X(controls[-1]).controlled_by(*controls[0:(len(controls)-1)]))
+        _temp = MCRY(controls[0:(len(controls)-1)], target, parameter/2.0)
+        gate_list += _temp
+    else:
+        gate_list.append(gates.CRY(controls[1], target, parameter/2.0, trainable=trainable))
+        gate_list.append(gates.CNOT(controls[0], controls[1]))
+        gate_list.append(gates.CRY(controls[1], target, -parameter/2.0, trainable=trainable))
+        gate_list.append(gates.CNOT(controls[0], controls[1]))
+        gate_list.append(gates.CRY(controls[0], target, parameter/2.0, trainable=trainable))
+
+    return gate_list
+
+def FEB_circuit(n_qubits, excitation, theta=0.0, trotter_steps=1, decompose=True) -> Circuit:
+
+    n_orbitals = len(excitation)
+    assert n_orbitals % 2 == 0, f"{excitation} must have an even number of items"
+
+    n_tuples = len(excitation) // 2
+    i_array = excitation[0:n_tuples]
+    a_array = excitation[n_tuples:]
+
+    ry_angle = 2.0*theta
+    if n_tuples % 4 in [2,3]: 
+        ry_angle *= -1
+
+    fwd_list = []
+
+    for _c in reversed(range(i_array[0]+2, a_array[-1])):
+        fwd_list.append(gates.CNOT(_c, _c-1))
+
+    if len(excitation) > 2:
+        fwd_list.append(gates.CZ(a_array[-1], i_array[0]+1))
+
+    for _a in reversed(a_array[0:-1]):
+        fwd_list.append(gates.CNOT(a_array[-1], _a))
+
+    for _i in reversed(i_array[0:-1]):
+        fwd_list.append(gates.CNOT(i_array[-1], _i))
+
+    fwd_list.append(gates.CNOT(a_array[-1], i_array[-1]))
+
+    for _ia in excitation:
+        if _ia not in [i_array[-1], a_array[-1]]:
+            fwd_list.append(gates.X(_ia))
+
+    if len(excitation) > 2:
+        mcry_gate = MCRY(excitation[:-1], excitation[-1], ry_angle)
+    else:
+        mcry_gate = [gates.CRY(i_array[0], a_array[0], ry_angle)]
+
+    gate_list = []
+
+    for _g in fwd_list:
+        gate_list.append(_g)
+
+    for _g in mcry_gate: 
+        gate_list.append(_g)
+
+    for _g in reversed(fwd_list):
+        gate_list.append(_g)    
+
+    circuit = Circuit(n_qubits)
+    if decompose is True:
+        for _g in gate_list:
+            controls = list(_g.control_qubits)
+            targets = list(_g.target_qubits)
+            qubit_span = controls + targets
+            qubits = list(range(n_qubits))
+            free_qubits = list(set(qubits) - set(qubit_span))
+            if len(free_qubits) == 0:
+                free_qubits = [excitation[-1]]
+            if len(controls) > 2:
+                mcx_decomposition = _g.decompose(*free_qubits)
+                circuit.add(mcx_decomposition)
+            else:
+                circuit.add(_g)
+    else:
+        circuit.add(gate_list)
+
+    return circuit
+
+
+