Qubit mixed state density matrix coordinates on a Bloch ball

  • #1
197
2
What are the coordinates on the 3D Bloch ball of a qubit's mixed state of the form:
##\rho=p_{00}|0\rangle \langle 0|+p_{01}|0\rangle \langle 1|+p_{10}|1\rangle \langle 0|+p_{11}|1\rangle \langle 1|##

451px-Bloch_sphere.svg.png
 
Last edited:

Answers and Replies

  • #3
Strilanc
Science Advisor
596
213
From stackoverflow: "Convert from qubit density matrix to Bloch vector"

Code:
def toBloch(matrix):
   [[a, b], [c, d]] = matrix
   x = complex(c + b).real
   y = complex(c - b).imag
   z = complex(d - a).real
   return x, y, z
In other words, yes you have to use the formula. But I'm not sure why you think it's impractical... it's just three additions/subtractions.
 

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