Decomposition of the Toffoli gate in terms of CNOT and single-qubit rotations

This notebooks demonstrates how a toffoli gate can be rewritten in terms of CNOT gates and single qubit gates, and verifies the equivalence of the two gate sequences by comparing their matrix representations. For more information about the toffoli decomposition, see Nielsen & Chuang, Sec. 4.3, p178.



In [1]:

    
from qutip import *



In [2]:

    
q = QubitCircuit(3, reverse_states=False)
q.add_gate("TOFFOLI", controls=[0, 2], targets=[1])



In [3]:

    
q.png









    Out[3]:



In [4]:

    
U = gate_sequence_product(q.propagators())

U.tidyup()









    Out[4]:





Quantum object: dims = [[2, 2, 2], [2, 2, 2]], shape = [8, 8], type = oper, isherm = True\begin{equation*}\left(\begin{array}{*{11}c}1.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 1.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 1.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 1.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 1.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.0\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.0 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.0 & 0.0 & 0.0\\\end{array}\right)\end{equation*}



In [5]:

    
q2 = q.resolve_gates()



In [6]:

    
q2.png









    Out[6]:



In [7]:

    
U2 = gate_sequence_product(q2.propagators())

U2.tidyup()









    Out[7]:





Quantum object: dims = [[2, 2, 2], [2, 2, 2]], shape = [8, 8], type = oper, isherm = True\begin{equation*}\left(\begin{array}{*{11}c}1.000 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 1.000 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 1.000 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 1.000 & 0.0 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 1.000 & 0.0 & 0.0 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.000\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.000 & 0.0\\0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 1.000 & 0.0 & 0.0\\\end{array}\right)\end{equation*}



In [8]:

    
U == U2









    Out[8]:





True

Versions



In [9]:

    
%reload_ext version_information

%version_information numpy, cython, scipy, matplotlib, qutip









    Out[9]:




Software Version
Python 3.4.0 64bit [GCC 4.8.2]
IPython 2.3.1
OS Linux 3.16.0 29 generic x86_64 with Ubuntu 14.10 utopic
numpy 1.9.1
cython 0.21.2
scipy 0.14.1
matplotlib 1.4.2
qutip 3.1.0
Tue Jan 13 13:21:05 2015 JST

Software	Version
Python	3.4.0 64bit [GCC 4.8.2]
IPython	2.3.1
OS	Linux 3.16.0 29 generic x86_64 with Ubuntu 14.10 utopic
numpy	1.9.1
cython	0.21.2
scipy	0.14.1
matplotlib	1.4.2
qutip	3.1.0
Tue Jan 13 13:21:05 2015 JST