Quantum discord of a bipartite system can be determined as:

$${D_A}({\rho _{AB}}) = I({\rho _{AB}}) - {J_A}({\rho _{AB}}),$$ The subscript of $A$ denotes that the measurement has been performed on the subsystem $A$. The mutual information is defined as - $$I({\rho _{AB}}) = S({\rho _A}) + S({\rho _B}) - S({\rho _{AB}}),$$

the classical correlation is defined as -

$${J_A}({\rho _{AB}}) = S({\rho _A}) - \mathop {\min }\limits_{\{ \Pi _I^A\} } \sum\limits_i {{p_i}S({\rho _{\left. B \right|i}})} ,$$ $$S({\rho _{\left. B \right|i}}) = {1 \over {{p_i}}}t{r_A}\left( {\Pi _i^A \otimes {I_B}} \right){\rho _{AB}}\left( {\Pi _i^A \otimes {I_B}} \right)$$

How does one calculate this quantity, computationally say, using Qutip or any other package/software, is there a code developed for this? Can anyone suggest an algorithm? Doing this analytically for any arbitrary density matrix, $\rho_{AB}$ is not feasible.

  • $\begingroup$ related github issue: github.com/qutip/qutip/issues/1450 $\endgroup$
    – poig
    Jun 30, 2022 at 12:41
  • $\begingroup$ Yes, but the thread provides no solution, and possibly no progress has happened since that conversation. I was hoping to find someone who might have done the computation and would have some advice. $\endgroup$
    – Paranoid
    Jun 30, 2022 at 12:46
  • 1
    $\begingroup$ groups.google.com/g/qutip/c/BvhlXRlEIPY you can ask Simon Cross here, for it. @Paranoid $\endgroup$
    – poig
    Jun 30, 2022 at 12:49


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