An Ideal Experiment to Determine the ‘Past of a Particle’ in the Nested Mach-Zehnder Interferometer

Marcin Wieśniak

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.

Rameez‐ul‐Islam, Muhammad Haroon Saeed, Hira Awan +2 more

F. A. Hashmi, Li, Fu, Shi‐Yao Zhu

In a recent article [Chin. Phys. Lett. 34, 020301 (2017)], Ben-Israel et al. have claimed that the experiment proposed in [Chin. Phys. Lett. 32, 050303 (2015)] to determine the past of a quantum particle in a nested Mach-Zehnder interferometer does not work, and they have proposed a modification to the experiment. We show that their claim is false, and the modification is not required.

Lev Vaidman A

An experiment with nested Mach-Zehnder interferometer [Phys. Rev. Lett. 111, 240402 (2013)] has been recently implemented with neutrons [Phys. Rev. A 97, 052111 (2018)]. Which-path information has been extracted from faint traces the neutrons left, providing operational meaning to "the particle's path". The authors of the neutron interference experiment criticised the conclusions obtained by the authors of the optical experiment. I refute the criticism and argue that the results of the neutron interference experiment actually support the surprising picture of the past of the particle in the nested Mach-Zehnder interferometer.

H. K. Zienkiewicz