Merge pull request #88 from qiboteam/dev_basisrotation

Basis rotation in arxiv:2207.03949 with standard gates

doc/source/tutorials/ansatz.rst

@@ -88,6 +88,10 @@ The following example demonstrates how the energy of the H2 molecule is affected
     |   0.2 |   0.673325849299  |
     -----------------------------
 
+..
+    Placeholder for basis rotation ansatz documentation
+
+
 .. _UCC Ansatz:
 
 Unitary Coupled Cluster Ansatz

examples/br_example.py

@@ -4,10 +4,11 @@
 """
 
 import numpy as np
+from qibo import Circuit, gates, models
 from qibo.optimizers import optimize
 from scipy.optimize import minimize
 
-from qibochem.ansatz.basis_rotation import br_circuit
+from qibochem.ansatz import basis_rotation
 from qibochem.ansatz.hf_reference import hf_circuit
 from qibochem.driver.molecule import Molecule
 from qibochem.measurement.expectation import expectation
@@ -19,7 +20,6 @@
 except ModuleNotFoundError:
     mol.run_psi4()
 
-
 # Diagonalize H_core to use as the guess wave function
 
 # First, symmetric orthogonalization of overlap matrix S using np:
@@ -47,35 +47,32 @@
 )
 
 
-def electronic_energy(parameters):
-    """
-    Loss function (Electronic energy) for the basis rotation ansatz
-    """
-    circuit = hf_circuit(mol.nso, mol.nelec)
-    circuit += br_circuit(mol.nso, parameters, mol.nelec)
-
-    return expectation(circuit, hamiltonian)
+def basis_rotation_circuit(mol, parameters=0.0):
 
+    nqubits = mol.nso
+    occ = range(0, mol.nelec)
+    vir = range(mol.nelec, mol.nso)
 
-# Build  a basis rotation_circuit
-params = np.random.rand(mol.nelec * (mol.nso - mol.nelec))  # n_occ * n_virt
+    U, theta = basis_rotation.unitary(occ, vir, parameters=parameters)
 
-best, params, extra = optimize(electronic_energy, params)
+    gate_angles, final_U = basis_rotation.givens_qr_decompose(U)
+    gate_layout = basis_rotation.basis_rotation_layout(nqubits)
+    gate_list, ordered_angles = basis_rotation.basis_rotation_gates(gate_layout, gate_angles, theta)
 
-print("\nResults using Qibo optimize:")
-print(f" HF energy: {mol.e_hf:.8f}")
-print(f"VQE energy: {best:.8f} (Basis rotation ansatz)")
-# print()
-# print("Optimized parameters:", params)
+    circuit = Circuit(nqubits)
+    for _i in range(mol.nelec):
+        circuit.add(gates.X(_i))
+    circuit.add(gate_list)
 
+    return circuit, gate_angles
 
-params = np.random.rand(mol.nelec * (mol.nso - mol.nelec))  # n_occ * n_virt
 
-result = minimize(electronic_energy, params)
-best, params = result.fun, result.x
+br_circuit, qubit_parameters = basis_rotation_circuit(mol, parameters=0.1)
+vqe = models.VQE(br_circuit, hamiltonian)
+vqe_result = vqe.minimize(qubit_parameters)
 
-print("\nResults using scipy.optimize:")
 print(f" HF energy: {mol.e_hf:.8f}")
-print(f"VQE energy: {best:.8f} (Basis rotation ansatz)")
-# print()
-# print("Optimized parameters:", params)
+print(f"VQE energy: {vqe_result[0]:.8f} (Basis rotation ansatz)")
+print()
+print("Optimized qubit parameters:\n", vqe_result[1])
+print("Optimizer message:\n", vqe_result[2])

src/qibochem/ansatz/__init__.py

@@ -1,9 +1,8 @@
 from qibochem.ansatz.basis_rotation import (
-    br_circuit,
-    givens_rotation_gate,
-    givens_rotation_parameters,
-    swap_matrices,
-    unitary_rot_matrix,
+    basis_rotation_gates,
+    basis_rotation_layout,
+    givens_qr_decompose,
+    unitary,
 )
 from qibochem.ansatz.hardware_efficient import hea
 from qibochem.ansatz.hf_reference import bk_matrix, bk_matrix_power2, hf_circuit