Fig. 4: Comparison of the theoretical and experimental density matrices.

The first and third columns represent the real part, and the second and fourth columns represent the imaginary part. The experimental density matrix refers to the density matrix of the experimental output state, which is represented by orange bars. The theoretical density matrix refers to the density matrix of the theoretical output state, which is represented by red bars. The letters at the lower left corner indicate the input states. The theoretical output states of the four states(\(\left|H\right\rangle ,\left|V\right\rangle ,\left|D\right\rangle ,\) and \(\left|L\right\rangle\)) involved in the estimation of the quantum process match the experimental results, and the theoretical output states of the two states(\(\left|A\right\rangle\) and \(\left|R\right\rangle\)) not involved in the estimation also match the experimental results. HH, HV, VH, and VV at the bottom of each graph represent the components of the density matrix.