  The delayed-choice quantum eraser has been intensively studied for the
wave-particle duality of a single photon in an interferometric system over the
last decades. Coincidence measurements between quantum erasers have also been
applied for the nonlocal quantum feature, satisfying the Bell inequality
violation. However, those quantum features have not been clearly understood
yet, resulting in the quantum mystery. Recently a coherence approach has been
tried for the quantum eraser to unveil the quantum mystery. Here, a phase
quantization of higher-order intensity products between coherently controlled
quantum erasers is presented using a quarter wave plate-induced phase shift
between orthogonal polarization bases of a single photon. Theoretical solutions
of both photonic-de-Broglie-wave-like quantum features and nonlocal quantum
correlations are presented for further discussions of quantum mechanics.
