Point defects in semiconductors are useful as quantum sensors, quantum emitters, and qubits for quantum computation. We have used ab initio quantum chemistry (supercell) calculations to model the photoluminescence of a new vanadium-nitrogen defect in diamond. Using ion implantation, we have attempted to synthesize this defect, and I will present spectroscopic analysis of our sample. Nanoscale positioning of defects is desired to improve the reliable coupling of defect centers to quantum photonic devices. I will discuss the merits of several methods for achieving this: introduction of functionalized seed molecules during diamond synthesis, laser annealing, and ion implantation. I will also present a scalable opto-thermal-mechanical printing method for additively releasing nanoparticles from a donor substrate and transferring them to a target substrate, such as a photonic device. Such integration is a crucial step towards realizing commercially scalable quantum sensing devices.
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, cholesteric liquid crystal hosts were used to create definite circular polarization of antibunched photons emitted by nanocrystal quantum dots. 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 Hong-Ou-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.
Results are presented here towards robust room-temperature SPSs based on fluorescence in nanocrystals: colloidal
quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral
photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed
plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities. The paper also provides short outlines of
other technologies for room-temperature single-photon sources.
Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.
Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a 1-D chiral photonic bandgap
cholesteric liquid crystal host. The resonance demonstrates coupling between quantum dot fluorescence and the
cholesteric microcavity. Observed at a band edge of a photonic stopband, this resonance has circular polarization due to
microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness.
The circular polarization dissymmetry factor ge of this resonance is ~1.3. We also demonstrate photon antibunching of a
single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric laser research,
in which so far only dyes under pulsed excitation were used, as well as for room-temperature single-photon source
applications.
Experimental results of two room-temperature, robust and efficient single-photon sources with definite circular and linear polarization using single-emitter fluorescence in cholesteric and nematic liquid crystal hosts are discussed. For single emitters, we used nanocrystal quantum dots, single color centers in nanodiamonds, and single dye molecules. Single-photon sources based on single emitters in liquid crystals are the room temperature alternatives to cryogenic single-photon sources base on semiconductor heterostructured quantum dots in microcavities prepared by molecular beam epitaxy.
Various single colloidal quantum dots were investigated in chiral liquid crystal 1-D photonic bandgap microcavities
for visible and telecom wavelengths. The microcavity environment provides circular polarization of definite
handedness. Narrow, circularly-polarized microcavity resonances of 3-5 nm width were observed on the band
edges of the stopbands.
Ruthenium is one material that has been suggested for use in preventing the oxidation of Mo/Si mirrors used in extreme ultraviolet (EUV) lithography. The optical constants of Ru have not been extensively studied in the EUV. We report the complex index of refraction, 1 - δ + iβ, of sputtered Ru thin films from 11-14 nm as measured via reflectance and transmission measurements at the Advanced Light Source at Lawrence Berkley National Laboratory. Constants were extracted from reflectance data using the reflectance vs. incidence angle method and from the transmission data by Lambert’s law. We compare the measured indices to previously measured values. Our measured values for delta are between 14-18% less than those calculated from the atomic scattering factors (ASF) available from the Center for X-ray Optics (CXRO). Our measured values of beta are between 5-20% greater than the ASF values.
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