  The heart of quantum mechanics is quantum superposition between orthogonal
bases of a single particle. In the particle nature of quantum mechanics,
quantum superposition is represented by probability amplitudes between mutually
exclusive natures such as orthogonal polarization bases. The delayed-choice
quantum eraser is for the post-determination of the photon nature, raising the
cause-effect relation issue. Over the last several decades, quantum erasers
have been intensively studied using nearly all kinds of photons. Here, the
macroscopic delayed-choice quantum eraser is experimentally demonstrated using
a continuous wave laser and discussed for quantum superposition in a
macroscopic regime. For this, a noninterfering Mach-Zehnder interferometer
composed of two polarizing beam splitters is chosen to manipulate polarization
bases of lights and to measure them in a delayed-choice manner via
polarization-basis projection.
