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Optimal storage of a single photon by a single intra-cavity atom
摘要： We theoretically analyze the efficiency of a quantum memory for single photons. The photons propagate along a transmission line and impinge on one of the mirrors of a high-finesse cavity. The quantum memory is constituted by a single atom within the optical resonator. Photon storage is realized by the controlled transfer of the photonic excitation into a metastable state of the atom and occurs via a Raman transition with a suitably tailored laser pulse, which drives the atom. Our study is supported by numerical simulations, in which we include the modes of the transmission line and we use the experimental parameters of existing experimental setups. It reproduces the results derived using input–output theory in the corresponding regimes and can be extended to compute dynamics where the input–output formalism cannot be straightforwardly applied. Our analysis determines the maximal storage efficiency, namely, the maximal probability to store the photon in a stable atomic excitation, in the presence of spontaneous decay and cavity parasitic losses. It further delivers the form of the laser pulse that achieves the maximal efficiency by partially compensating parasitic losses. We numerically assess the conditions under which storage based on adiabatic dynamics is preferable to non-adiabatic pulses. Moreover, we systematically determine the shortest photon pulse that can be efficiently stored as a function of the system parameters.
关键词： single photon,three level system,storage efficiency,optical cavity,single atom,quantum memory
更新于2025-09-23 15:21:01
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Hybrid atom-molecule quantum walks in a one-dimensional optical lattice
摘要： We study hybrid atom-molecule quantum walks in one-dimensional optical lattices with two interacting bosonic atoms which may be converted into a molecule. The hybrid atom-molecule energy bands include a continuum band and two isolated bands, which respectively correspond to scattering states and dressed bound states (DBSs). Because of the atom-molecule coupling, the DBSs may appear even in the absence of atom-atom interaction. From an initial state of two atoms occupying the same site, in addition to independent quantum walks which correspond to scattering states, correlated quantum walks appear as a signature of DBSs. Even if the atom-atom interaction and the atom-molecule coupling are much stronger than the tunneling strengths, independent quantum walks may still appear under certain resonant conditions. The correlated quantum walks show two light cones with different propagation velocities, which can be analytically explained by the effective tunneling strengths of the two different DBSs. Furthermore, the effective nearest-neighbor tunneling of DBSs can be suppressed to zero, which can be explained by the destructive interference between the atomic pair and the molecule.
关键词： Quantum walks,dressed bound states,atom-molecule coupling,tunneling,optical lattices
更新于2025-09-23 15:21:01
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Crystalline structure, electronic and lattice-dynamics properties of NbTe2
摘要： Layered-structure materials are currently relevant given their quasi-2D nature. Knowledge of their physical properties is currently of major interest. Niobium ditelluride possesses a monoclinic layered-structure with a distortion in the tellurium planes. This structural complexity has hindered the determination of its fundamental physical properties. In this work, NbTe2 crystals were used to elucidate its structural, compositional, electronic and vibrational properties. These findings have been compared with calculations based on density functional theory. The chemical composition and elemental distribution at the nanoscale were obtained through atom probe tomography. Ultraviolet photoelectron spectroscopy allowed the first determination of the work function of NbTe2. Its high value, 5.32 eV, and chemical stability allow foreseeing applications such as contact in optoelectronics. Raman spectra were obtained using different excitation laser lines: 488, 633, and 785 nm. The vibrational frequencies were in agreement with those determined through density functional theory. It was possible to detect a theoretically-predicted, low-frequency, low-intensity Raman active mode not previously observed. The dispersion curves and electronic band structure were calculated, along with their corresponding density of states. The electrical properties, as well as a pseudo-gap in the density of states around the Fermi energy are characteristics proper of a semi metal.
关键词： Electronic band structure,Ultraviolet photoelectron spectroscopy,Density functional theory,Atom probe tomography,Niobium ditelluride,Layered-structure materials,Raman spectra,Density of states,Semimetal
更新于2025-09-23 15:21:01
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Clustered atom-replaced structure in single-crystal-like metal oxide
摘要： By means of metal organic deposition using tri?uoroacetates (TFA-MOD), we replaced and localized two or more atoms in a single-crystalline structure having almost perfect orientation. Thus, we created a new functional structure, namely, clustered atom-replaced structure (CARS), having single-crystal-like metal oxide. We replaced metals in the oxide with Sm and Lu and localized them. Energy dispersive x-ray spectroscopy results, where the Sm signal increases with the Lu signal in the single-crystalline structure, con?rm evidence of CARS. We also form other CARS with three additional metals, including Pr. The valence number of Pr might change from 3+ to approximately 4+, thereby reducing the Pr–Ba distance. We directly observed the structure by a high-angle annular dark-?eld image, which provided further evidence of CARS. The key to establishing CARS is an equilibrium chemical reaction and a combination of additional larger and smaller unit cells to matrix cells. We made a new functional metal oxide with CARS and expect to realize CARS in other metal oxide structures in the future by using the above-mentioned process.
关键词： superconductor,YBCO,quasi-liquid network model,clustered atom-replaced structure,cluster,TFA-MOD
更新于2025-09-23 15:21:01
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Light-Induced Coherence in an Atom-Cavity System
摘要： We demonstrate a light-induced formation of coherence in a cold atomic gas system that utilizes the suppression of a competing density wave (DW) order. The condensed atoms are placed in an optical cavity and pumped by an external optical standing wave, which induces a long-range interaction mediated by photon scattering and a resulting DW order above a critical pump strength. We show that the light-induced temporal modulation of the pump wave can suppress this DW order and restore coherence. This establishes a foundational principle of dynamical control of competing orders analogous to a hypothesized mechanism for light-induced superconductivity in high-Tc cuprates.
关键词： atom-cavity system,dynamical control,optical standing wave,light-induced coherence,density wave order
更新于2025-09-23 15:21:01
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Synthesis of a Novel Fluorescent Cyanide Chemosensor Based on Photoswitching Poly(pyrene-1-ylmethyl-methacrylate-random-methyl methacrylate-random-methacrylate spirooxazine)
摘要： The photoswitching poly(pyrene-1-ylmethyl-methacrylate-random-methyl methacrylate-random-methacrylate spirooxazine) was synthesized via atom transfer radical polymerization and characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, and differential scanning calorimetry (DSC). The obtained copolymer exhibited the capability of erasable and rewritable photo-imaging, making it a potential candidate for optical data storage materials. Moreover, the copolymer also showed the sensing ability for cyanide anions effect in aqueous solutions.
关键词： spirooxazine,chemosensor,photoswitching polymers,atom transfer radical polymerization
更新于2025-09-23 15:21:01
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Application of Atom Probe Tomography to Complex Microstructures of Laser Additively Manufactured Samples
摘要： Additive Manufacturing (AM) technologies have gained increasing interest across multiple industrial sectors ranging from biomedical to aerospace. AM is not only used for prototyping, but also for tooling as well as for final part production. The computer-controlled, layer-by-layer building up process allows for increased design freedom enabling to produce almost any shape. Additional benefits are potential resource efficiency, increased product customization and lightweight design. Two prominent metal-based laser AM (LAM) techniques are laser powder bed fusion (LPBF) and laser metal deposition (LMD). In LPBF, a focused laser beam is scanned over a bed filled with metal powder to locally melt and fuse the powder to produce fully dense metal parts. The next layer of powder is then distributed and the laser scans again. LMD is a nozzle-based AM process in which a focused laser beam creates a melt pool in the build’s surface. Metallic powder is then injected into the melt pool through a nozzle. The 3D part is built by moving the nozzle/laser assembly forward track by track and layer by layer. Material produced by LAM exhibits a unique thermal history: initially, the material is cooled rapidly from the liquid state in the meltpool. Subsequently, the material experiences a cyclic reheating, the so-called intrinsic heat treatment (IHT), as neighboring tracks and further layers are deposited during the LAM process. Consequences of this thermal history are very complex, sometimes hierarchical microstructures with inhomogeneities at scales ranging from nanometers up millimeters. Fully understanding and characterizing these microstructures is challenging and requires the combination of methods spanning a similar range: from light optical microscopy (LOM) to electron microscopy to atom probe tomography (APT). Here we present examples how APT can deliver valuable information on complex microstructures to better understand the IHT, rapid solidification as well as phase separation in different metallic alloys. Here I will discuss examples in steel, Al- and Ni-based superalloys, and high entropy alloys (HEA).
关键词： Laser Additive Manufacturing,Additive Manufacturing,Phase Separation,Microstructures,Atom Probe Tomography,Rapid Solidification,Intrinsic Heat Treatment
更新于2025-09-23 15:19:57
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Formation of Quantum Vortices at the Ionization of an Atom by an Ultrashort Laser Pulse: Two- and Three-Dimensional Cases
摘要： Quantum vortices formed at the barrier-suppression ionization of an atom by an ultrashort laser pulse have been studied theoretically and numerically. The ionization of a hydrogen atom is considered in the two-dimensional space and the ionization of an atom in the zero-range potential approximation is considered in the three-dimensional space. The resulting analytical expressions imply that the localization of quantum vortices in the three-dimensional space can be predicted by analyzing the two-dimensional model.
关键词： hydrogen atom,zero-range potential approximation,ultrashort laser pulse,Quantum vortices,barrier-suppression ionization
更新于2025-09-23 15:19:57
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Absolute density measurement of hydrogen atom in inductively coupled Ar/H2 plasmas using vacuum ultraviolet absorption spectroscopy
摘要： The absolute density measurement of atomic species such as hydrogen is crucial for plasma processing because of their strong chemical reactivity. In this work, to measure the hydrogen atom density in Ar/H2 inductively coupled plasmas (ICP), the self-absorption-applied vacuum ultraviolet absorption spectroscopy (VUVAS) is studied with a micro-hollow cathode H2/He discharge lamp (MHCL) emitting VUV light (Lyman alpha line; Lα 121.56 nm). The absolute density of hydrogen atoms in the ICP is investigated for various powers (50 W–850 W) in the low pressure region (30 mTorr–50 mTorr). The hydrogen density in remote plasma region is shown to vary from 2.1 × 1011 cm?3 to 1.25 × 1012 cm?3 with respect to plasma power.
关键词： VUV absorption spectroscopy,Low-pressure,Self-absorption,Hydrogen atom density,inductively coupled plasma
更新于2025-09-23 15:19:57
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Three-dimensional measurement of Mg dopant distribution and electrical activity in GaN by correlative atom probe tomography and off-axis electron holography
摘要： The distribution and electrical activity of p-type doping (Mg) in gallium nitride (GaN) grown by metal organic chemical vapor deposition was investigated by correlating atom probe tomography (APT) and off-axis electron holography. APT results revealed that high Mg concentrations promote the formation of Mg-rich clusters. This is associated with the formation of pyramidal inversion domains (PIDs). The direct measurement of the doping concentration outside the clusters provided by APT suggests a saturation in the p-type electrical activity for Mg concentrations above 7 × 1019 cm?3. Maps of the electrostatic potential provided by off-axis electron holography confirm that the highest carrier concentration was achieved in the regions with the highest dopant concentration of 2 × 1020 cm?3, despite the presence of a high density of Mg-rich clusters revealed by APT. The correlation of these techniques suggests that PIDs are not the major cause of the reduction in electrostatic potential.
关键词： Mg doping,GaN,atom probe tomography,electrical activity,off-axis electron holography
更新于2025-09-23 15:19:57