example_QX2_general_unitary.py

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# -*- coding: utf-8 -*-
"""
Created on Fri Jun 26 14:42:56 2020
Copyright 2020 Peter Rakyta, Ph.D.

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.

@author: Peter Rakyta, Ph.D.
"""




# cerate unitary q-bit matrix
from scipy.stats import unitary_group
from squander import utils
import numpy as np



def create_custom_gate_structure_QX2(qbit_num):
    r"""
    This method is called to create custom gate structure for the decomposition on IBM QX2

    """

    from squander import Circuit


    # creating an instance of the wrapper class Circuit
    Circuit_ret = Circuit( qbit_num )



    disentangle_qbit = qbit_num - 1 


        

    for qbit in range(0, disentangle_qbit ):


        Layer = Circuit( qbit_num )


        if qbit == 0:

            # add U3 gate to the block    
            Layer.add_U3( 0 )                 
            Layer.add_U3( disentangle_qbit ) 

            # add CNOT gate to the block
            Layer.add_CNOT( 0, disentangle_qbit)

        elif qbit == 1:


            Layer.add_U3( 0 )                 
            Layer.add_U3( 1 ) 

            # add CNOT gate to the block
            Layer.add_CNOT( 0, 1)



        elif qbit == 2:

            # add U3 gate to the block  
            Layer.add_U3( 2 )                 
            Layer.add_U3( disentangle_qbit ) 

            # add CNOT gate to the block
            Layer.add_CNOT( 2, disentangle_qbit )

         

        Circuit_ret.add_Circuit( Layer )



    return Circuit_ret



from squander import N_Qubit_Decomposition


qbit_num = 4



matrix_size = int(2**qbit_num)
   
# creating a random unitary to be decomposed
Umtx = unitary_group.rvs(matrix_size)



decomp = N_Qubit_Decomposition( Umtx.conj().T )



reordered_qbits = (0,1,3,2)

# adding custom gate structure to the decomposition
decomp.Reorder_Qubits( reordered_qbits )



gate_structure = { 4: create_custom_gate_structure_QX2(4), 3: create_custom_gate_structure_QX2(3)}        


# adding custom gate structure to the decomposition
decomp.set_Gate_Structure( gate_structure )



decomp.set_Max_Layer_Num( {4: 60, 3:16} )



decomp.set_Optimization_Blocks( 20 )



decomp.Start_Decomposition()



revert_qbits = (1,0,2,3)             

# adding custom gate structure to the decomposition
decomp.Reorder_Qubits( revert_qbits )



decomp.List_Gates()



quantum_circuit = decomp.get_Qiskit_Circuit()


import numpy.linalg as LA
    
# the unitary matrix from the result object
decomposed_matrix = utils.get_unitary_from_qiskit_circuit( quantum_circuit )
product_matrix = np.dot(Umtx,decomposed_matrix.conj().T)
phase = np.angle(product_matrix[0,0])
product_matrix = product_matrix*np.exp(-1j*phase)
    
product_matrix = np.eye(matrix_size)*2 - product_matrix - product_matrix.conj().T
# the error of the decomposition
decomposition_error =  (np.real(np.trace(product_matrix)))/2
       
print('The error of the decomposition is ' + str(decomposition_error))