Quantum Circuit - 2's complement subtractor

Qubit_Subtractor

# %% [markdown]
# Implementing Two's complements subtractor using quantum gates.

# %%
from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit, Aer, execute


# %%
simulator = Aer.backends('qasm_simulator')[0]


# %%
def fullAdder(circuit, a, b, c, d):
    circuit.ccx(a, b, d)
    circuit.cx(a, b)
    circuit.ccx(b, c, d)
    circuit.cx(b, c)
    circuit.cx(a, b)
    # circuit.barrier()


# %%
def fourbitAdder(circuit, qRegisters):
    #                          C
    #                    A  B  S  C
    fullAdder(circuit, qRegisters[3], qRegisters[7], qRegisters[11], qRegisters[10])
    fullAdder(circuit, qRegisters[2], qRegisters[6], qRegisters[10], qRegisters[9])
    fullAdder(circuit, qRegisters[1], qRegisters[5], qRegisters[9], qRegisters[8])
    fullAdder(circuit, qRegisters[0], qRegisters[4], qRegisters[8], qRegisters[12])


# %%
TC_qr = QuantumRegister(13, name='q')
Twos_Complement = QuantumCircuit(TC_qr, name='Twos_Complement')

# 1s Complement
Twos_Complement.x(0)
Twos_Complement.x(1)
Twos_Complement.x(2)
Twos_Complement.x(3)

# For Adding 0001
Twos_Complement.x(7)

# Adding Input(B) and 0001
fourbitAdder(Twos_Complement, [0,1,2,3,4,5,6,7,8,9,10,11,12])

# Resetting Inputs
Twos_Complement.x(0)
Twos_Complement.x(1)
Twos_Complement.x(2)
Twos_Complement.x(3)
Twos_Complement.x(7)

Twos_Complement.to_gate()
Twos_Complement.draw('mpl')


# %%
B = QuantumRegister(4, name='b')
One = QuantumRegister(4, name='o')
B_twos_complement = QuantumRegister(4, name='s')
Final_Carry = QuantumRegister(2, name='fc')

A = QuantumRegister(4, name='a')
Sum_A_B2s = QuantumRegister(4, name='x')

Final_Answer = QuantumRegister(4, name='y')

C = ClassicalRegister(5, name='c')
QC = QuantumCircuit(B, One, B_twos_complement, Final_Carry, A, Sum_A_B2s, C,Final_Answer)

# Input A
QC.x(A[0])
# QC.x(A[1])
QC.x(A[2])
# QC.x(A[3])

# Input B
QC.x(B[0])
# QC.x(B[1])
# QC.x(B[2])
QC.x(B[3])

QC.barrier()

QC.append(Twos_Complement, [B[0], B[1], B[2], B[3], One[0], One[1], One[2], One[3], B_twos_complement[0],
          B_twos_complement[1], B_twos_complement[2], B_twos_complement[3], Final_Carry[0]])

QC.barrier()

fourbitAdder(QC, [B_twos_complement[0], B_twos_complement[1], B_twos_complement[2], B_twos_complement[3], A[0], A[1],
                  A[2], A[3], Sum_A_B2s[0], Sum_A_B2s[1], Sum_A_B2s[2], Sum_A_B2s[3], Final_Carry[0]])

QC.barrier()

# QC.measure([Sum_A_B2s[3], Sum_A_B2s[2], Sum_A_B2s[1],
#            Sum_A_B2s[0], Final_Carry[0]], [0, 1, 2, 3, 4])

# QC.draw('mpl')


# %%
QC.measure([Final_Carry[0]], [4])

# QC.reset([B_twos_complement[0], B_twos_complement[1], B_twos_complement[2], B_twos_complement[3]])
# QC.reset([One[0], One[1], One[2], One[3]])
# QC.reset([Final_Carry[0]])

QC.append(Twos_Complement, [Sum_A_B2s[0], Sum_A_B2s[1], Sum_A_B2s[2], Sum_A_B2s[3], One[0], One[1], One[2], One[3], Final_Answer[0],
          Final_Answer[1], Final_Answer[2], Final_Answer[3], Final_Carry[1]]).c_if(C[4],0)

QC.cx(Sum_A_B2s[0],Final_Answer[0]).c_if(C[4],1)
QC.cx(Sum_A_B2s[1],Final_Answer[1]).c_if(C[4],1)
QC.cx(Sum_A_B2s[2],Final_Answer[2]).c_if(C[4],1)
QC.cx(Sum_A_B2s[3],Final_Answer[3]).c_if(C[4],1)

# %%
QC.measure([Final_Answer[3], Final_Answer[2], Final_Answer[1],
           Final_Answer[0]], [0, 1, 2, 3])


# %%
QC.draw('mpl')

# %%
job = execute(QC, simulator)
result = job.result()
result.get_counts(QC)