Spectra in nested Mach–Zehnder interferometer experiments

李福, Hashmi, 张俊香 +1 more

Huei Peng

H. K. Zienkiewicz

G. N. Nikolaev

The author of the comment on my work [1] states that the proposed modification of the scheme of the experiment reported in [2] is improper and that the experiment faithfully demonstrates a discontinuous trace of photons.It is difficult to agree with this statement because of the absence of clear and well-founded (see below).In [1], I discussed the recent experiment [2] with a nested Mach-Zehnder interferometer.The authors treated the experiment so that the past of photons is not described by continuous trajectories because photons are detected inside the inner Mach-Zehnder interferometer and are not detected outside it.The idea of a small modification of the scheme of the experiment [2] has been proposed just to detect photons at the input of the inner Mach-Zehnder interferometer.Instead of the vibration of the mirror, the direction of polarization of light is modulated in this scheme.Further, in one of the arms of the inner Mach-Zehnder interferometer, this modulation is converted into a shift of the light beam of orthogonal polarization, which is then transformed to the original polarization.The realization of the idea is as follows.A birefringent plate, a phase compensator, and two polarizers that oriented at the angle of 45° and in parallel to the initial polarization are placed in one of the arms of the inner Mach-Zehnder interferometer.The same polarizers are placed in the other two arms of the nested Mach-Zehnder interferometer.The author of the comment states that such a modification is improper because it "violates the faithfulness of the experiment because it causes different transformations of the polarization record at E into a signal at the detector, depending on the path the beam takes."The author of the comment also claims that "the signal at the detector does not present a faithful indication of the trace inside the interferometer" in the absence of con-

fu Li, F. A. Hashmi, Jun-Xiang Zhang +1 more

An ideal experiment is designed to determine the past of a particle in the nested Mach-Zehnder interferometer (MZI) by using standard quantum mechanics with quantum non-demolition measurements. We find that when the photon reaches the detector, it only follows one arm of the outer interferometer and leaves no trace in the inner MZI. When it goes through the inner MZI, it cannot reach the detector. Our result obtained from the standard quantum mechanics contradicts the statement based on two-state vector formulism, 'the photon did not enter the (inner) interferometer, the photon never left the interferometer, but it was there'. Therefore, the statement and also the overlapping claim are incorrect.

Carlo Tarsitani, Fabrizio Logiurato