Paradox of photons disconnected trajectories being located by means of “weak measurements” in the nested Mach–Zehnder interferometer

Abstract

Recently, a scheme based on the method of weak measurements to register the trajectories of photons passing through a nested Mach-Zehnder interferometer was proposed [L. Vaidman, Phys. Rev. A 87, 052104 (2013)] and then realized [A. Danan, D. Farfurnik, S. Bar-Ad, et al., Phys. Rev. Lett. 111, 240402 (2013)]. Interpreting the results of the experiment, the authors concluded that "the photons do not always follow continuous trajectories". It is shown in this work that these results can be easily and clearly explained in terms of traditional classical electrodynamics or quantum mechanics implying the continuity of all possible paths of photons. Consequently, a new concept of disconnected trajectories proposed by the authors of work [Phys. Rev. Lett. 111, 240402 (2013)] is unnecessary.

When Photons Are Lying about Where They Have Been

“…Vaidman, together with his collaborators, performed an experiment demonstrating a surprising trace of the photons in nested interferometers [ 1 ] (see Figure 1 ). These results became the topic of a very large controversy [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ].…”

Erasing the which-path information of photons

“…And yet, physicists are still not sure the trajectory a quantum particle took from the source by only measuring it in a detector [11][12][13][14][15]. Such discussions mostly focus on interferometers, such as double slit interferometer [1,11,[16][17][18] and Mach-Zehnder interferometer (MZI) [3][4][5][6][7][8][9][10][19][20][21]. For example, Wheler et al [1,2] tried to infer the past path of photons through the output of photon detector in a double-slit interferometer and found a counter-factual result: we can't infer the past of photons, because photons can hide their past.…”

Response to the comment on “Paradox of photons disconnected trajectories being located by means of ‘weak measurements’ in the nested Mach–Zehnder interferometer” (JETP Letters 105, 152 (2017))

“…

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 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.

…”

“…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.…”