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Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields
摘要： We report on the appearance of a structure at low energies in the photoelectron momentum distribution of the hydrogen atom exposed to two-color counterrotating bicircular laser fields. These structures, which arise due to ac-Stark-shifted resonances, break the threefold symmetry, typical for the ω ? 2ω bicircular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, which passes through the ac-Stark-shifted state, and show how the underlying Rydberg state population depend on the field strength and pulse duration.
关键词： bicircular laser fields,Rydberg state population,ac-Stark-shifted resonances,photoelectron momentum distribution,hydrogen atom
更新于2025-09-19 17:13:59
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Quantum Squeezing of the Field of a Single-Atom Laser under Conditions of a Variable Coupling Constant
摘要： A nonstationary regime of squeezed-light generation by a single-atom laser is investigated. Dependences of the quantum-squeezing parameter and radiation intensity on modulation frequency of the atom–field coupling constant are obtained. It is demonstrated that a resonance appears at the modulation frequency equal to twice the average coupling constant, which leads to a more efficient quantum squeezing in a nonstationary harmonic regime than in the case of a stationary regime for the same values of the relaxation and pump parameters.
关键词： single-atom laser,coupling constant,squeezed light
更新于2025-09-19 17:13:59
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Atoma??photon entanglement near a plasmonic nanostructure
摘要： We investigate the atom–photon entanglement between a four-level double V-type quantum system and a linearly polarized ?eld near a plasmonic nanostructure in the presence of a static magnetic ?eld. It is demonstrated that the magneto-optical effect can affect the atom–photon entanglement only when the atom is near the plasmonic nanostructure. We show that atom–photon entanglement increases when the quantum system is placed near the plasmonic nanostructure in order to modi?cation of the spontaneous decays of the quantum system. It is demonstrated that the degree of entanglement (DEM) increases by increasing the intensity of the linearly polarized ?eld when the quantum system is close to the surface of the plasmons. Moreover, we ?nd that near the plasmonic nanostructure, the static magnetic ?eld has a major role in increasing the steady-state DEM so that the DEM is completely demolished in the absence of the static magnetic ?eld. Finally, it is shown that the atom–photon entanglement near a plasmonic nanostructure is destroyed by free space decay rate.
关键词： degree of entanglement,static magnetic ?eld,atom–photon entanglement,plasmonic nanostructure,spontaneous emission
更新于2025-09-19 17:13:59
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Four-membered red iridium( <scp>iii</scp> ) complexes with Ira??Sa??Ca??S structures for efficient organic light-emitting diodes
摘要： Three sulfur atom contained ligands (diphenylcarbamodithioate (dpdtc), di-p-tolylcarbamodithioate (medtc) and bis(4-(trifluoromethyl)phenyl)carbamodithioate (cf3dtc)) were prepared for three red iridium(III) complexes. All (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc) complexes were synthesized rapidly at room temperature in 5 min with high yields owing to strong coordination ability between sulfur and iridium atoms, in which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as main ligand. Three Ir(III) complexes show distinct PL emissions at the range of 617 - 629 nm with high phosphorescence quantum yields up to of 83%, respectively. With these complexes as dopants, the organic light-emitting devices (OLEDs) with the double-emissive-layer structure of ITO/ HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/ TAPC ((bis(4-(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/ Ir(III) complexes: TCTA (4,4',4''-tris(carbazol-9-yl)-triphenylamine) (12 wt%, 10 nm)/ Ir(III) complexes: 26DCzppy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12 wt%, 10 nm)/ TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/ LiF (1 nm)/ Al (100 nm) achieved good performances. In particular, the device employing (tfmpqz)2Ir(cf3dtc) complex exhibits the champion performances with a maximum luminance of 30 740 cd m-2 and a maximum external quantum efficiency of 26.10%, respectively.
关键词： phosphorescence quantum yields,sulfur atom,iridium(III) complexes,external quantum efficiency,OLEDs
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Spectroscopic Probing of Retardation Effects in the Casimir-Polder Interaction: A Theoretical Study
摘要： Spectroscopic probing of retardation effects in the Casimir-Polder interaction: a theoretical study. Lennard-Jones theory describes the atom-surface interaction as the instantaneous interaction between a fluctuating dipole and its image predicting a surface induced shift of the atomic energy levels given by -C3/z3, where z is the atom-surface distance and C3 is the van der Waals (vdW) coefficient. In Casimir-Polder theory, demonstrated experimentally with ground state atoms in ~1μm thick metallic cavities [1], atom-surface interactions arise from the modification of vacuum fluctuations next to a dielectric boundary. More recently, Casimir-Polder theory has been tested with ground state cold atoms at intermediate distances from a dielectric surface [2]. Nevertheless, testing the limits of the van der Waals law in the extreme near field remains an important experimental challenge. Additionally, excited state atoms are also of fundamental importance, as their interaction with surfaces can also be of resonant nature. This is of particular interest when atomic dipole transitions couple resonantly to surface polaritons, allowing for exotic near field effects. Selective reflection spectroscopy is a major experimental method testing Casimir-Polder interaction of excited state atoms in the near field. Up to now, experimental results have been interpreted exclusively under the prism of the van der Waals approximation. Here, we show calculations of the fully retarded, spectroscopically relevant, Casimir-Polder potentials for the 6S1/2→6P1/2 and 6S1/2→5D5/2 (Fig.1a) Cs transitions (difference between the Casimir-Polder potentials between probed states) taking into account temperature corrections [3]. The dipole forbidden 6S1/2→6D5/2 transition was recently probed by selective reflection spectroscopy [4]. We demonstrate that accounting for a fully retarded potential leads to significantly different predictions of selective reflection spectra compared to a -C3/z3 vdW approximation. Surprisingly, a vdW model when allowing for an adjustable, ad hoc, van der Waals coefficient can accommodate these differences (Fig1b). However, careful analysis shows that this ad hoc coefficient is not a constant but strongly depends on transition linewidth (collisional broadening) as seen in Fig1c. This is because the contribution of atoms to the experimental spectra depends on their relative detuning, i.e. Casimir-Polder shift divided by the transition linewidth. As the linewidth increases, atoms closer to the surface become more ‘resonant’ with the excitation lasers increasing their contribution [5]. Our analysis shows that by increasing the collisional broadening in selective reflection spectroscopy one can tune the experimental probing depth thus probing atoms that are closer to the surface. This can provide an important experimental tool for measuring the effects of retardation in atom-surface potentials of low lying atomic transitions using selective reflection spectroscopy. Retardation effects can have an impact in atom-metamaterial interactions where plasmons can be tuned in resonance with D1 and D2 lines of alkali atoms at near infrared wavelengths [6].
关键词： van der Waals coefficient,selective reflection spectroscopy,Casimir-Polder interaction,atom-surface interaction,retardation effects
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Zn:MgO:PPLN Waveguides for Rb Cold Atom Trap Based Quantum Gravitometry in a CubeSat
摘要： Satellite based experiments require laser systems that are compact and efficient, which are robust against vibration, radiation and thermal cycling. Supported by Innovate UK’s Quantum Technology ‘Cold Atom Space PAyload (CASPA)’ project we have fabricated PPLN (Periodically Poled Lithium Niobate) ridge waveguides to act as efficient frequency converters for rubidium atom cooling via second harmonic generation (SHG) of telecoms lasers. CASPA is a technology demonstrator for magneto-optical cooling within a micro CubeSat laying the foundations for novel gravitometry and global positioning techniques. With respect to the particular environment of operation we have developed single mode ridge waveguides with metal indiffusion and dicing. We fabricate PPLN ridge waveguides by firstly high-voltage poling of z-cut magnesium doped lithium niobate, then deposit and thermally indiffuse Zn to create planar optical confinement, followed by ultra-precision ductile dicing to define ridge waveguides and coupling facets. Our non-AR coated waveguides have produced optical to optical efficiencies of up to 22.0 %, producing 44.7 mW of SHG with 203 mW of transmitted pump. The 2nd moment MFD was calculated to be 10.8 and 10.0 μm in the x and y axes, respectively, allowing efficient mode matching to standard telecommunication fibre. With a free space launch we have measured an average insertion loss, over multiple dies, of -1.3 dB, for 4 cm long waveguides that are non-AR coated. When comparing to other ridge PPLN waveguides this is a 3.7 dB improvement over competing examples of a 5 cm bonded and thinned device and a 1.9 dB improvement for a 1 cm proton exchange device. These low insertion losses can be attributed to both the symmetric pump mode of the waveguides enabling efficient mode matching and low amounts of optical scattering from waveguide sidewall roughness. We have shown ductile dicing to produce an average surface roughness of 0.29 nm (Sa) on waveguide facets in a single processing step.
关键词： CubeSat,rubidium atom cooling,second harmonic generation,ridge waveguides,PPLN
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Multi-Qubit Registers of Individually Addressable Solid-State Defect Centers
摘要： Mesoscopic ensembles of qubits offer a platform for near-term applications in quantum technologies, as well as for studying many-body physics. Key in exploiting these systems is the ability to coherently control constituent qubits in a manner that leaves the quantum states of neighboring qubits unperturbed. Atom-like emitters in solids have emerged as a promising platform for computing, communications, and sensing. In particular, their long coherence times, coherent optical transitions, and the ability to couple to nearby long-lived nuclear spins make them excellent candidates for building medium-scale registers of coupled qubits. Here, we present progress towards producing and controlling such individually addressable ensembles. Our approach relies on the natural inhomogeneous distribution of optical transitions for solid-state color centers. This distribution allows us to excite individual centers even in tightly-grouped clusters. With this, we first demonstrate super-resolution localization and readout of individual nitrogen vacancy (NV) centers in diamond. We probe a system of three NV centers, demonstrating localization with a mean precision of 0.74 nm. While super-resolution imaging of NV centers has been achieved with other techniques, our approach uniquely allows for individual readout of single NVs in a cluster in a manner that maintains the states of nearby spins. We perform simultaneous control of two spin populations in a cluster of NVs, demonstrating preservation of coherence of one population during the optical readout of another. Lastly, we discuss recent work towards scalable creation of such clusters and techniques for producing systems of coupled spins with various defect centers.
关键词： spin-spin coupling,quantum technologies,super-resolution localization,qubits,solid-state color centers,nitrogen vacancy centers,many-body physics,atom-like emitters
更新于2025-09-16 10:30:52
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Dislocation Mass-Transfer and Electrical Phenomena in Metals under Pulsed Laser Influence
摘要： The influence of moving dislocations on mass-transfer and the phenomena, accompanying it in pulse-deformed metals is studied in a real-time. Transport of self-interstitial atoms (SIAs) by mobile edge dislocations in crystal with FCC lattice is investigated by molecular dynamics. A strain rate (106 s-1) and dislocation density (1010 – 1012 cm-2) in simulated crystal corresponds to a laser effect in a Q-factor mode. The experimental investigations in a real-time are performed by recording of electrical signal induced by the laser pulse irradiation of metal foils of different crystal structures.
关键词： stresses,amorphous foil,dislocation,laser pulse,electrokinetic phenomena,interstitial atom,mass-transfer,elastic field,strain
更新于2025-09-16 10:30:52
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Cryo-focused ion beam preparation of perovskite based solar cells for atom probe tomography
摘要： Focused-ion beam lift-out and annular milling is the most common method used for obtaining site specific specimens for atom probe tomography (APT) experiments and transmission electron microscopy. However, one of the main limitations of this technique comes from the structural damage as well as chemical degradation caused by the beam of high-energy ions. These aspects are especially critical in highly-sensitive specimens. In this regard, ion beam milling under cryogenic conditions has been an established technique for damage mitigation. Here, we implement a cryo-focused ion beam approach to prepare specimens for APT measurements from a quadruple cation perovskite-based solar cell device with 19.7% efficiency. As opposed to room temperature FIB milling we found that cryo-milling considerably improved APT results in terms of yield and composition measurement, i.e. halide loss, both related to less defects within the APT specimen. Based on our approach we discuss the prospects of reliable atom probe measurements of perovskite based solar cell materials. An insight into the field evaporation behavior of the organic-inorganic molecules that compose the perovskite material is also given with the aim of expanding the applicability of APT experiments towards nano-characterization of complex organo-metal materials.
关键词： field evaporation,solar cells,APT,atom probe tomography,FIB,cryo-focused ion beam,perovskite,halide loss
更新于2025-09-16 10:30:52
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Atomistic kinetic Monte Carloa??Embedded atom method simulation on growth and morphology of Cua??Zna??Sn precursor of Cu <sub/>2</sub> ZnSnS <sub/>4</sub> solar cells
摘要： An atomistic kinetic Monte Carlo coupled with the embedded-atom method is used to simulate film growth and morphology evolution of a Cu–Zn–Sn precursor of Cu2ZnSnS4 solar cells by single-step electrodeposition. The deposition and diffusion events of three different metallic atoms are described by the simulation. Moreover, the multibody Cu–Zn–Sn potential is used to calculate diffusion barrier energy. The effects of process factors, including temperature and electrode potential, on the cross-section morphology and surface roughness are explored, while keeping the elemental composition ratios constant. The lowest roughness with the smoothest morphology is obtained at the optimal parameters. The distribution and transformation behaviors of cluster sizes are investigated to describe the alloy film growth process. Furthermore, the comparison between deposition events and diffusion events reveals that deposition events depend primarily on individual deposition rates of different metallic atoms, but diffusion events are mainly dependent on the interaction of metallic atoms. The film morphology evolution is visualized by three-dimensional configuration with increasing numbers of atoms, which suggests a competing mechanism between nucleation and growth of the thin film alloy.
关键词： Cu–Zn–Sn precursor,film growth,Cu2ZnSnS4 solar cells,electrodeposition,atomistic kinetic Monte Carlo,morphology evolution,embedded-atom method
更新于2025-09-16 10:30:52