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#!/usr/bin/env python
"""Grover's quantum search algorithm example."""
from sympy import pprint
from sympy.physics.quantum import qapply
from sympy.physics.quantum.qubit import IntQubit
from sympy.physics.quantum.grover import (OracleGate, superposition_basis,
WGate, grover_iteration)
def demo_vgate_app(v):
for i in range(2**v.nqubits):
print('qapply(v*IntQubit(%i, %r))' % (i, v.nqubits))
pprint(qapply(v*IntQubit(i, v.nqubits)))
qapply(v*IntQubit(i, v.nqubits))
def black_box(qubits):
return True if qubits == IntQubit(1, qubits.nqubits) else False
def main():
print()
print('Demonstration of Grover\'s Algorithm')
print('The OracleGate or V Gate carries the unknown function f(x)')
print('> V|x> = ((-1)^f(x))|x> where f(x) = 1 when x = a (True in our case)')
print('> and 0 (False in our case) otherwise')
print()
nqubits = 2
print('nqubits = ', nqubits)
v = OracleGate(nqubits, black_box)
print('Oracle or v = OracleGate(%r, black_box)' % nqubits)
print()
psi = superposition_basis(nqubits)
print('psi:')
pprint(psi)
demo_vgate_app(v)
print('qapply(v*psi)')
pprint(qapply(v*psi))
print()
w = WGate(nqubits)
print('WGate or w = WGate(%r)' % nqubits)
print('On a 2 Qubit system like psi, 1 iteration is enough to yield |1>')
print('qapply(w*v*psi)')
pprint(qapply(w*v*psi))
print()
nqubits = 3
print('On a 3 Qubit system, it requires 2 iterations to achieve')
print('|1> with high enough probability')
psi = superposition_basis(nqubits)
print('psi:')
pprint(psi)
v = OracleGate(nqubits, black_box)
print('Oracle or v = OracleGate(%r, black_box)' % nqubits)
print()
print('iter1 = grover.grover_iteration(psi, v)')
iter1 = qapply(grover_iteration(psi, v))
pprint(iter1)
print()
print('iter2 = grover.grover_iteration(iter1, v)')
iter2 = qapply(grover_iteration(iter1, v))
pprint(iter2)
print()
if __name__ == "__main__":
main()
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