It don't have to give error's.

enter code here 

In [4]:from sympy import symbols from sympy.core.trace import Tr from sympy.matrices.matrices import Matrix from IPython.core.display import display_pretty from sympy.printing.latex import * from sympy.physics.quantum.cartesian import * from sympy.physics.quantum.qubit import * from sympy.physics.quantum.density import *

      %load_ext sympyprinting

TODO: Add examples of simple qubit usage

Qt Operations on Qubits

In [2]:q1 = Qubit('10110') q2 = Qubit('01010') d = Density( [q1, 0.6], [q2, 0.4] )

Trace one bit

       t = Tr(d,[0])

       display_pretty(t.doit())