Single-photon experiments with liquid crystals for quantum science and quantum engineering applications

Abstract

We present here our results on using liquid crystals in experiments with nonclassical light sources:(1) single-photon sources exhibiting antibunching (separation of all photons in time), which are key components for secure quantum communication systems, and (2) entangled photon source with photons exhibiting quantum interference in a Hong-Ou-Mandel interferometer. In the first part, both nematic and cholesteric liquid crystal hosts were used to create definite linear or circular polarization of antibunched photons emitted by different types of single emitters (dye molecules, nanocrystal quantum dots, nanodiamonds with color centers, etc.). If the photon has unknown polarization, filtering it through a polarizer to produce the desired polarization for quantum key distribution with bits based on polarization states of photons will reduce by half the efficiency of a quantum cryptography system. In the first part, we also provide our results on observation of a circular polarized microcavity resonance in nanocrystal quantum dot fluorescence in a 1-D chiral photonic bandgap cholesteric liquid crystal microcavity. In the second part of this paper with indistinguishable, time-entangled photons, we demonstrate our experimental results on simulating quantum-mechanical barrier tunnelling phenomena. A HongOu-Mandel dip (quantum interference effect) is shifted when a phase change was introduced on the way of one of entangled photons in pair (one arm of the interferometer) by inserting in this arm an electrically controlled planar-aligned nematic liquid crystal layer between two prisms in the conditions close to a frustrated total internal reflection. By applying different AC-voltages to the planar-aligned nematic layer and changing its refractive index, we can obtain various conditions for incident photon propagation -from total reflection to total transmission. Measuring changes of tunnelling times of photon through this structure with femtosecond resolution permitted us to answer some unresolved questions in quantum-mechanical barrier tunnelling phenomena.Keywords: polarized single-photon source, antibunching, nanocrystal quantum dots, NV-color-centers in nanodiamonds, nematic, cholesteric liquid crystals, Hong-OuMandel interferometer, entangled photons, quantum mechanical barrier tunnelling time, double-prism structure, frustrated total internal reflection A c c e p t e d M a n u s c r i p t

Sustainable education in the age of the second quantum revolution: fifteen years of the University of Rochester National Science Foundation supported efforts

“…Liquid crystal examples were used in an OPT 204 lecture workshop on nonclassical light sources [31][32][33] . Entangled sources, indistinguishable photons, and a Hong-Ou-Mandel interferometer 34,35 were described, and examples of experiments with liquid crystal structures in a Hong-Ou-Mandel interferometer at the Institute of Optics were discussed [36][37][38][39] .…”

Undergraduate program in nanoscience and nanoengineering: five years after the National Science Foundation grant including two pandemic years

“…35,36 Entangled sources, indistinguishable photons, and a Hong-Ou-Mandel interferometer 37 were described, and examples of experiments with 1D photonic bandgap CLC structures in a Hong-Ou-Mandel interferometer at the Institute of Optics were discussed. [38][39][40][41] In addition, students learned about single-photon sources based on single-emitter fluorescence in planar-aligned liquid crystal hosts and other micro-and nanostructures for tailoring the properties of the emitted single photons. 35,36 5 Pedagogical Research on Students' Learning How do we know whether students are learning?…”