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concurrence calculation of qubit system

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AVM
AVM 2020-1-24
回答： Ibrahim Issah 2021-3-18
I need to calcualte the concurrenec for the given density matrix. Pl somebody see my code and solve my issue.
clc
close all
function c=concurrence(rho)
rho=1/2*[0 0 0 0;0 1 -1 0;0 -1 1 0;0 0 0 0];
y=[0 -1i; 1i 0];
R=rho*kron(y,y)*conj(rho)*kron(y,y);
% Real is needed since MATLAB always adds a small imaginary part ...
e=real(sqrt(eig(R)));
e=-sort(-e);
c=max(e(1)-e(2)-e(3)-e(4),0)
end
The concurrenec is not coming. Pl help me to get that.

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回答（1 个）

Ibrahim Issah
Ibrahim Issah 2021-3-18
%% intialize %%
clc
close all
clear
%%%%%%%%%%%%%
%% density matrix%%%%
rho=1/2*[0 0 0 0;0 1 -1 0;0 -1 1 0;0 0 0 0];
%%%%%%% pauli matrix%%%%%%%%%%
y=[0 -1i; 1i 0];
%%% p and ptilda %%%%%%%
R=rho*kron(y,y)*conj(rho)*kron(y,y);
% Real is needed since MATLAB always adds a small imaginary part ...
e=real(sqrt(eig(R)));
e=-sort(-e);
c=max(e(1)-e(2)-e(3)-e(4),0);
disp(c);
%% Apparently you don't need any function for this since your density matrix is already defined. Thank you.

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