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Quantum Cryptography and Teleportation
Published in F.J. Duarte, Quantum Optics for Engineers, 2017
A realization of the Ekert approach has been published by Naik et al. (2000). In their experiment these authors use spontaneous parametric down conversion to produce pairs of entangled photons propagating in divergent paths. The receiving optics includes a PS set composed of a randomly driven liquid crystal (LC) followed by a half-wave plate (HWP). The photon then proceeds to a polarizing beam splitter prior to arrival to a detector. An approximate depiction of this type of optical configuration is provided in Figure 19.7.
Nanoscale Etching and Deposition
Published in R. Mohan Sankaran, Plasma Processing of Nanomaterials, 2017
Nathan Marchack, Jane P. Chang
There are other top-down techniques discussed in the literature to extend lithographic patterning beyond the diffraction limit. Among these are nanoimprint lithography (NIL),101 quantum interferometric optical lithography (QIOL),102 surface plasmon resonant interference nanolithography (SPRINT),103 and metamaterial-based “superlenses.”104 The NIL method utilizes mechanical molding of polymer materials to create features, which theoretically could overcome the diffraction limit; however, plasma etching is still deeply involved in the process—from the creation of the template molds to the removal of residual polymer on the substrate. However, this approach offers the possibility of hybridization; by implanting metal pads into the template mold it can be used as both a conventional lithographic mask as well as an NIL tool. QIOL is based on the concept of nonclassical entangled photon-number states and theoretically allows for the patterning of features with a minimum CD smaller than the diffraction limit by a factor of N, where N in this case is the number of photons entangled at a time, and also the number absorbed by the substrate. Entangled photon pairs can be generated by spontaneous parametric down-conversion and allow for lithography below the typical limits of diffraction.102 SPRINT relies on the principle that illumination light can be guided with a prism to couple with surface plasmons to obtain a new state with a much shorter wavelength and higher field intensity than that of the illumination light. The resulting enhanced optical field close to the metal mask can then cause localized exposure of a thin resist layer below the mask.103 The superlens concept hinges heavily on “negative index media” (NIM) (i.e., materials with a negative index of refraction). Engineering NIM allows for the enhancement of evanescent waves, which carry fine details about the object but are confined to the near field and subsequently become lost by conventional glass lenses. When utilized in conjunction with a coupling element, the enhanced evanescent waves can be coupled into propagating waves, which makes far-field detection possible. A variation of this idea is the hyperlens, which uses an artificial metamaterial to transfer deep subwavelength information into the far field by a two-stage process. First, evanescent waves are enhanced through surface resonance, followed by conversion into a propagation wave at the exit surface by means of a designed surface scatter.104 Such novel techniques provide examples of expanding the possibilities of plasma etching.
Photon statistics of twisted heralded single photons
Published in Journal of Modern Optics, 2020
Nijil Lal, Anindya Banerji, Ayan Biswas, Ali Anwar, R. P. Singh
Single photon sources are one of the most important quantum sources of light finding applications in quantum key distribution, random number generation, quantum computing with photons and quantum metrology (1–4). One of the most popular technique to produce a single photon source is to use the spontaneous parametric down conversion (SPDC) process in a nonlinear crystal (5, 6). In this process, one photon of the pump is converted to two photons of lower energies, which propagate in a certain direction following the conservation laws of energy and momentum. Since the two down converted photons are generated at the same time, detection of one photon heralds the presence of the other (7, 8). Therefore, single photon sources obtained by using this technique are generally called as heralded single photon sources. Optical vortices or Laguerre Gaussian (LG) beams with zero radial index are gaining popularity in implementing various quantum information protocols (9, 10) as they provide an extra degree of freedom in the form of orbital angular momentum (OAM) (11, 12) that can be measured using standard experimental techniques (13–15). Optical vortices of different orders or azimuthal indices form different spatial modes of light with their characteristic properties (16–20). Intensity correlations of classical optical vortices are found to have dependence on the order of the vortex while scattered from a rotating ground-glass plate (16). Such studies evoke interest in the correlation properties of single photons carrying OAM generated in spontaneous processes such as parametric down conversion. In the present work, starting with the Gaussian mode, we take different orders of vortices as a pump to the nonlinear crystal and study the intensity correlations of down converted photons to characterize them for single photon sources of light including twisted single photons.