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Strongly inhomogeneous distribution of spectral properties of silicon-vacancy color centers in nanodiamonds
摘要： The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that SiV centers in nanodiamonds exhibit a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range ≈730–742 nm and broad linewidths between 5 and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 and 835 nm, but narrow linewidths from below 1 up to 4 nm. Supported by ab initio Kohn–Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of a new class of silicon-related defects. Whereas single photon emission is demonstrated for defect centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.
关键词： diamond,single photons,density functional theory calculations,color centers,optical emission,nanodiamond
更新于2025-09-19 17:15:36
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Coherence turned on by incoherent light
摘要： One of the most pertinent problems in the debate on non-trivial quantum effects in biology concerns natural photosynthesis. Since sunlight is composed of thermal photons, it was argued to be unable to induce quantum coherence in matter, and that quantum mechanics is therefore irrelevant for the dynamical processes following photoabsorption. Our present analysis of a toy 'molecular aggregate'—composed of two dipole–dipole interacting two-level atoms treated as an open quantum system—however shows that incoherent excitations indeed can trigger persistent, coherent dynamics in both the site and the exciton bases: we demonstrate that collective decay processes induced by the dipole–dipole interactions create coherent intermolecular transport—regardless of the coherence properties of the incoming radiation. Our analysis shows that the steady state coherence is mediated by the population imbalance between the molecules and, therefore, increases with the energy difference between the two-level atoms. Our results establish the importance of collective decay processes in the study of ultrafast photophysics, and especially their potential role to generate stationary coherence in incoherently driven quantum transport.
关键词： molecular aggregate,energy transfer,coherence,dipole–dipole interaction,thermal photons
更新于2025-09-19 17:15:36
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Development of a high resolution LaGPS imaging detector with pulse shape discrimination capability of different types of radiations
摘要： Ce doped (Gd,La)2Si2O7 (LaGPS) is a new scintillator which has high light output and is a promising candidate for high resolution radiation imaging detectors. Thus we developed a radiation imaging detector using a LaGPS plate combined with a position sensitive photomultiplier tube (PSPMT) and evaluated the performance. We found that the decay times of LaGPS were different with the types of radiations and the separations of the images of the different types of radiations were possible using pulse shape discrimination. The spatial resolution for Am-241 alpha particles (5.5 MeV) was better than 0.31 mm FWHM and the energy resolution was 11 % FWHM. The spatial resolution for Sr–Y-90 beta particles was ～0.6 mm FWHM and those for Co-57 gamma photons (122 keV) and Cs-137 X-ray (～35 keV) were better than 0.6 mm FWHM and ～0.8 mm FWHM, respectively. The decay times for alpha particles, beta particles, and gamma photons were 143 ns, 124 ns, and 119 ns, respectively. With these different decay times, the separation of alpha particles and gamma photons or beta particles was possible using the pulse shape discrimination. We conclude that the developed LaGPS imaging detector has high resolution for all types of radiations and is also capable of the simultaneous imaging and separating the different types of radiations.
关键词： Alpha particles,Imaging,Pulse shape discrimination,Beta particles,Gamma photons,Decay time,LaGPS
更新于2025-09-19 17:15:36
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From physics to fixtures to food: current and potential LED efficacy
摘要： Light-emitting diodes (LEDs) have enabled a historic increase in the conversion of electric energy to photons, but this is approaching a physical limit. The theoretical maximum efficiency occurs when all input energy is converted to energy in photosynthetic photons. Blue LEDs can be 93% efficient, phosphor-converted “whites” 76% efficient, and red LEDs 81% efficient. These improvements open new opportunities for horticultural lighting. Here we review (1) fundamental physics and efficiency of LEDs, (2) the current efficacy of LEDs, (3) the effect of spectral quality on crop yield, and (4) the potential efficacy of horticultural fixtures. Advances in the conversion of photons to yield can be achieved by optimization of spectral effects on plant morphology, which vary among species. Conversely, spectral effects on photosynthesis are remarkably similar across species, but the photons conventional (400–700 nm) may need to be modified. The upper limit of LED fixture efficacy is determined by the LED package efficacy multiplied by four factors inherent to all fixtures: thermal droop, driver (power supply) current droop, inefficiencies, and optical losses. With current LED technology, the calculations indicate efficacy limits of 3.4 μmol J?1 for white + red fixtures, and 4.1 μmol J?1 for blue + red fixtures. Adding optical protection from water and high humidity reduces these values by ~10%. We describe tradeoffs between peak efficacy and cost.
关键词： spectral quality,fixture efficacy,horticultural lighting,LEDs,photosynthetic photons
更新于2025-09-19 17:13:59
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Interaction between Microwave and Mesoscopic Circuits in Cavity-circuit Quantum Electrodynamics
摘要： Mesoscopic electric circuits can exhibit a large number of effects relevant to quantum mechanics, quantum electrodynamics and quantum statistics. The topic presented here can be identified as an analog of conventional cavity quantum electrodynamics, where the quantum objects are multilevel atoms and quantized optical fields (photons), namely, a theoretical subject called “cavity-circuit quantum electrodynamics”, where the atoms are replaced with quantum mesoscopic circuits, will be developed. We will study the quantum characteristics of the interaction between the quantum mesoscopic circuits and the quantized electromagnetic field at microwave frequencies. These issues include quantum entangled eigenstates of two coupled mesoscopic circuits, time evolution of the circuit energy quanta (governed by the time-dependent Schr?dinger equation) and entanglement transfer between external photons and mesoscopic circuit energy quanta. Since there is inevitable electromagnetic interaction such as mutual capacitance and inductance coupling between two neighboring circuits, the quantum effects resulting from the aforementioned quantized circuit coupling would unavoidably affect the relevant processes in quantum computing devices and hence they deserve consideration in some issues of quantum information.
关键词： Quantum computing,Microwave photons,Quantum entanglement,Mesoscopic circuits,Quantum electrodynamics
更新于2025-09-19 17:13:59
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Strain tunable quantum dot based non-classical photon sources
摘要： Semiconductor quantum dots are leading candidates for the on-demand generation of single photons and entangled photon pairs. High photon quality and indistinguishability of photons from different sources are critical for quantum information applications. The inability to grow perfectly identical quantum dots with ideal optical properties necessitates the application of post-growth tuning techniques via e.g. temperature, electric, magnetic or strain fields. In this review, we summarize the state-of-the-art and highlight the advantages of strain tunable non-classical photon sources based on epitaxial quantum dots. Using piezoelectric crystals like PMN-PT, the wavelength of single photons and entangled photon pairs emitted by InGaAs/GaAs quantum dots can be tuned reversibly. Combining with quantum light-emitting diodes simultaneously allows for electrical triggering and the tuning of wavelength or exciton fine structure. Emission from light hole exciton can be tuned, and quantum dot containing nanostructure such as nanowires have been piezo-integrated. To ensure the indistinguishability of photons from distant emitters, the wavelength drift caused by piezo creep can be compensated by frequency feedback, which is verified by two-photon interference with photons from two stabilized sources. Therefore, strain tuning proves to be a flexible and reliable tool for the development of scalable quantum dots-based non-classical photon sources.
关键词： quantum dot,on-chip,piezoelectric crystal,entangled photons,fine structure splitting,strain tuning
更新于2025-09-19 17:13:59
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Chiral coupling of magnons in waveguides
摘要： We theoretically investigate the collective excitations of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnon-photon coupling can be tuned to be chiral, i.e., magnons only couple with photons propagating in one direction, leading to an asymmetric transfer of angular momentum and energy between the magnets. A large enhancement of the magnon number population can be achieved at an edge of a long chain of magnets. The chain also supports standing waves with low radiation efficiency that are inert to the chirality.
关键词： collective excitations,magnon-photon coupling,ferromagnets,chiral coupling,waveguide photons
更新于2025-09-19 17:13:59
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The use of optical fibers as passageways for the scintillation light produced in CaF <sub/>2</sub> (Eu) powder in water for low-level tritiated water measurement
摘要： A solid scintillation counting (SSC) system which uses the mixture of CaF2(Eu) powder and tritiated water inside the chamber room will be developed for the measurement of low-level tritiated water. However, the coincidence detection e?ciency and net count rate might be limited by the photon absorption in the chamber of the SSC detector. This paper discusses the feasibility of using light guide ?bers as the optical passageway in the chamber room by Geant4 simulation. The simulation results show that the performance of the detector can be improved by using wavelength-shifting ?bers as optical passageway in the chamber. The detector can maintain a 4.2% coincidence detection e?ciency at a 6 cm chamber thickness, and the detection limit can be as low as 0.47 Bq/mL under 10 min measurement. As a result, using wavelength-shifting ?bers as optical passageways in the chamber room of the SSC system is possible and e?ective.
关键词： Radiation monitoring,Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc),Very low-energy charged particle detectors,Solid state detectors
更新于2025-09-16 10:30:52
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Wigner Representation for Investigation of Entangled Photon Evolution in Four-Wave Mixing Process within a Fiber Ring Resonator
摘要： The aim of this study is to analyze the quantum correlation of entangled photons for four-wave mixing process within Kerr nonlinear susceptibility χ(3) of an optical fiber ring resonator. The main system Hamiltonian composes of two types of coupling photon modes, including pumping and parametric-down conversion. Wigner representation is applied to the Heisenberg equation of motion derived from the system Hamiltonian in order to obtain the corresponding stochastic equations of motion in a c-number. Quantum trajectories obtained from the stochastic equation of motion of photon states are then derived. Finally, the entanglement inseparability criteria for a pair of entangled photon from a numerical approach is also satisfied.
关键词： Four-Wave Mixing,Quantum Correlation,Entangled Photons
更新于2025-09-16 10:30:52
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Photons and charges from colloidal doped semiconductor quantum dots
摘要： The utility of colloidal semiconductor quantum dots as a source of photons and charge carriers for photonic and photovoltaic applications has created a large field of research focused on tailoring and broadening their functionality beyond what an exciton can provide. One approach towards expanding the range of characteristics of photons and charge carriers from quantum dots is through doping impurity ions (e.g. Mn2+, Cu+, and Yb3+) in the host quantum dots. In addition to the progress in synthesis enabling fine control of the structure of the doped quantum dots, a mechanistic understanding of the underlying processes correlated with the structure has been crucial in revealing the full potential of the doped quantum dots as the source of photons and charge carriers. In this review, we discuss the recent progress made in gaining microscopic understanding of the photophysical pathways that give rise to unique dopant-related luminescence and the generation of energetic hot electrons via exciton-to-hot electron upconversion.
关键词： doping impurity ions,charge carriers,photons,hot electrons,colloidal semiconductor quantum dots,photophysical pathways
更新于2025-09-16 10:30:52