We revisit a variation of the experiment based on Thomas Young’s double-slit interferometer. Previous demonstrations of the quantum eraser experiment were performed with the aid of path interferometers. Section snippets Revisiting the traditional which-way quantum eraser That is to say, the results presented give a fast probing method to characterize the different channel’s perturbation, and would be useful for determining in an easy measurement what would be feasible for a quantum communication channel down fiber. In our particular case, a fiber optic link is formed by many different channels, introducing some kind of perturbation depending on the DoF that carries the encoded information. This work establishes the basis for a simple detection technique to quantify perturbations introduced by the environment, particularly in the communication channel, between the source and the detection section. Here we report on the comparison of a quantum eraser in free-space and a step-index fiber using the OAM and polarization DoF provided by vector modes. This approach provides a useful tool for applications in optical communication in both free-space and optical fibers ,, , a hot topic nowadays due to the realization of a pending bandwidth “capacity crunch”. For example, the decrease of quality in the interferometric measurement can be associated to the perturbations introduced by the system. Thus, the visibility of the interferometric pattern can be directly related to the properties of the system. Importantly, the double-slit experiment and its modern variations allows to link the which-way information provided by the whole system with the interference pattern produced at the detection plane . The traditional quantum eraser experiment ,, ,, ,, ,, , and its delayed choice versions, ,, are related to the complementarity principle formulated by Bohr in 1928 , which states that photons can behave indistinctly as particles or waves but cannot be observed as both simultaneously. The modern view of wave-particle duality has opened new research avenues, for example in the development of novel measurement schemes, as the ones based on quantum non-demolition . Other DoF can also be found to demonstrate this particular type of correlations, e.g., in the case of generating entanglement between momentum and polarization in a single photon , or even using intense beams . In quantum optics, photons entangled in OAM and polarization have been demonstrated to violate a Bell-like inequality , being able also to tune its entanglement or photon indistinguishability , similarly to the analogous version of a quantum eraser scheme using OAM and polarization . In particular, in the field of optical communication and quantum information, their high dimensional encoding capabilities have raised attention ,, , due to their potential applications in free-space and optical fibers . Vector beams have gained significant amount of interest in a great variety of research fields at both the classical and the quantum levels. Here, the physical paths are replaced by two components of one degree of freedom, e.g., two values of OAM.
The combination of two DoF, orbital angular momentum (OAM) and polarization in a non-separable fashion, known as vector beams, allows to perform novel versions of the two-slit experiments. Remarkably, interferometric phenomena are not restricted to two-path interferometers it is also possible to observe interference of beams traveling along the same path, but using different degrees of freedom (DoF). Upon propagation, these two new sources interfere with each other to produce an interference pattern of spatial fringes. The double-slit experiment is a two-path interferometer in which a light source blocked by a screen with two slits is split into two new sources traveling along different paths. The most revered demonstration of the wave-like nature of photons was performed by Young in 1804, in his famous double-slit experiment , followed by modern variations ,,. The concept of which-way information has profound implications in the study of coherence of light, giving a different scope to the historical wave-particle duality.
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