density2={{0.75, 0.25 - 0.25 I}, {0.25 + 0.25 I, 0.25}};

density2t = {{0.75,0.5 (0.5 (1. E^(0.2 t) Cos[0.1 t]-1. E^(0.2 t) Sin[0.1 t])-(0. +0.5 I) (1. E^(0.2 t) Cos[0.1 t]+1. E^(0.2 t) Sin[0.1 t]))},{0.5 (0.5 (1. E^(0.2 t) Cos[0.1 t]-1. E^(0.2 t) Sin[0.1 t])+(0. +0.5 I) (1. E^(0.2 t) Cos[0.1 t]+1. E^(0.2 t) Sin[0.1 t])),0.25}};

r0x = Tr[density2.PauliMatrix[1]]//FullSimplify
r0y = Tr[density2.PauliMatrix[2]]//FullSimplify
r0z = Tr[density2.PauliMatrix[3]]//FullSimplify

r2x = Tr[density2t.PauliMatrix[1]] // FullSimplify
r2y = Tr[density2t.PauliMatrix[2]] // FullSimplify
r2z = Tr[density2t.PauliMatrix[3]] // FullSimplify