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The quantum coherent control of a quantum system with high fidelity is rather important in quantum computation and quantum information processing. Many control techniques are used to reach these targets, such as resonant excitation, adiabatic passages, shortcuts to adiabaticity, and composite pulses. However, for a single pulse to realize population transfer, a tiny external error has a slight influence on the final population. The repeated application of the same pulse will greatly amplify the error effect, making it easy to be detected. Here, we propose to measure small control errors in three-level quantum systems through a coherent amplification of their effects using several coherent control techniques. For the two types of Hamiltonian with an SU(2) dynamic symmetry, we analyze how the fidelity of the population transfer is affected by the Rabi frequency error and static detuning deviation based on the pulse sequence with alternating and same phases, respectively. The results show that the sensitivity of detecting these errors can be effectively amplified by control pulse sequences. Furthermore, we discuss the efficiency of sensing the two errors with the control techniques by comparing the full width at half maximum of the population profiles. The results provide an accurate and reliable way for detecting the weak error in three-level quantum systems by repeatedly applying the coherent control pulse. [ABSTRACT FROM AUTHOR]

We describe the design and implementation of a compact laser system for the pulsed optically pumped (POP) rubidium (Rb) cell atomic clock. The laser system includes packaged optics for sub-Doppler absorption, acousto-optic modulation and light beam expansion, and dedicated electronics for laser diode reliable single-mode operation and laser frequency stabilization. With beat measurements between two identical laser systems, the laser frequency stability was found to be ${3.0}\times {10}^{-{12}}$ for averaging times from 1 to 60 s and it reached ${3.5}\times {10}^{-{12}}$ at 10 000 s averaging time. Based on the compact laser system, the short-term stability of the Rb cell atomic clock in pulsed regime was approximately ${2.7}\times {10}^{-{13}}\,\, {\tau }^{-\text {1/2}}$ , which is in reasonable agreement with the estimated ${2.37}\times {10}^{-{13}}\,\, {\tau } ^{-\text {1/2}}$. The compact laser system is significant in terms of the development of transportable and high-performance Rb atomic clock prototypes. [ABSTRACT FROM AUTHOR]

We propose a method to continuously frequency shift a target laser that is frequency stabilized by a reference laser, which is several hundreds of nanometers detuned. We demonstrate the technique using the $\mathrm {5S_{1/2}} \rightarrow \mathrm {5P_{3/2}} \rightarrow \mathrm {29D_{5/2}}$ Rydberg transition in 87Rb vapor and lock the 482 nm target laser to the 780 nm reference laser using the cascaded electromagnetically induced transparency signal. The stabilized frequency of the target laser can be shifted by about 1.6 GHz by phase modulating the reference laser using a waveguide-type electro-optical modulator. This simple method for stable frequency shifting can be used in atomic or molecular physics experiments that require a laser frequency scanning range on the order of several GHz. [ABSTRACT FROM AUTHOR]

We explore the carrier doping effect on magnetic properties of defective graphene with single-atom vacancy by performing spin-polarized density functional theory calculations. Theoretical results show that both hole and electron dopings can effectively modify the local magnetic moments. Besides, we also demonstrate that hole doping can greatly enhance the magnetic coupling, increasing the critical temperature of magnetism, which is absent in electron doping case. The coupling enhanced mechanism can be well understood by the different variation trends of pz-derived states around the Fermi level under hole doping. Thus, our results provide a practical way to tune the magnetism of defective graphene. [ABSTRACT FROM AUTHOR]

In this tutorial, a classical Langevin equation, a classical Markov equation, and a quantum Langevin equation are used to model the amplification and attenuation of an optical signal. Equations are derived for the photon-number moments (mean and variance). All three approaches produce the same moment equations. In the first approach, the moments of the noise sources must be specified (using physical insight), whereas in the second and third approaches, they are determined self-consistently and satisfy the shot-noise rule: The number variance is driven at a rate that equals the sum of the moduli of the rates in the mean equation. [ABSTRACT FROM AUTHOR]

Single-atom impurities and other atomic-scale defects can notably alter the local vibrational responses of solids and, ultimately, their macroscopic properties. Using high-resolution electron energy-loss spectroscopy in the electron microscope, we show that a single substitutional silicon impurity in graphene induces a characteristic, localized modification of the vibrational response. Extensive ab initio calculations reveal that the measured spectroscopic signature arises from defect-induced pseudo-localized phonon modes—that is, resonant states resulting from the hybridization of the defect modes and the bulk continuum—with energies that can be directly matched to the experiments. This finding realizes the promise of vibrational spectroscopy in the electron microscope with single-atom sensitivity and has broad implications across the fields of physics, chemistry, and materials science. [ABSTRACT FROM AUTHOR]

• CO 2 RR performance of TM doped boron nitride fullerene (BNF) explored. • Mn-B 23 N 24 and Fe-B 23 N 24 exhibited high activity and selectivity for CO 2 RR to CH 4. • Curvature effect of BNF on catalytic performance analyzed by pyramidalization angle. • TM-N 3 center with pyramidalization angle of about 26° exhibits the highest activity. • N coordinating environment are more favorable for regulating catalytic activity. Electrocatalytic carbon dioxide reduction reaction (CO 2 RR) is currently one of the most promising methods for conversion of excessive CO 2 emission. In this study, the electrocatalytic performance of transitional-metal atoms anchored on defective boron nitride fullerene of different size were systematically investigated by density functional theory study (TM= Sc, Ti, V, Cr, Mn, Fe, Ni, Zn, and Mo). The results showed Mn-B 23 N 24 and Fe-B 23 N 24 exhibited high activity and selectivity for CO 2 RR to CH 4. Analysis of the high catalytic performance origin indicates the binding energy of *CO and *OH intermediates (E b (*CO) and E b (*OH)) can server as descriptors for the catalytic performance. The curvature effect of the boron nitride fullerene surface on the catalytic performance was analyzed by the so-called pyramidalization angle which shows TM-N 3 center with the pyramidalization angle of about 26° exhibits the highest activity. The analysis of the coordination environment also reveals B defects are more favorable for regulating catalytic activity compared with N defects. Especially, compare with the Mn doped BN nanosheet, the limiting potential is significantly decreased from −0.64 V on the flat nanosheet to −0.25 V on TM doped B defective B 24 N 24 , highlighting the importance of the curvature effect on the CO 2 RR performance. This study demonstrated that metal-doped boron nitride fullerene with appropriate curvature is high potential to be efficient CO 2 RR catalysts, providing valuable insights for the rational design of CO 2 RR electrocatalysts with high-efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

• The ORR on 3d, 4d, and 5d transition metals doped C 7 N 3 (TM-C 7 N 3) are studied by DFT. • All screened TM-C 7 N 3 possess considerable catalytic activity for ORR. • The coordination N atoms can remarkably improve the ORR activity on most of TM-C 7 N 3. • The Rh-C 7 N 3 exhibits best ORR catalytic activity with the overpotential value of 0.32V in this work. Single-atom catalysts (SACs) possess promising potential as materials to catalyze oxygen reduction reaction (ORR) on account of high atomic utilization efficiency, tunable electronic structure, and exceptional catalytic performance. The ORR activities of graphite carbonitride (g-C 7 N 3) supported 3d, 4d, and 5d transition metals are investigated. Eleven kinds of TM-C 7 N 3 structures have been found to have good stability by computing formation energy and dissolution potential. Furthermore, density of states analysis shows a strong interaction of the metal atom and the coordination N atoms, which gives satisfactory stability of TM-C 7 N 3. Among eleven TM-C 7 N 3 , the binding energy of reaction species on Rh-C 7 N 3 , Ni-C 7 N 3 , and Pt-C 7 N 3 are closer to those of Pt(111), showing that they have good ORR activity. In addition, good linear relationships exist between the adsorption free energy of *OH (∆ G *OH) and that of *OOH and *O, implying that ∆ G *OH can be put forward as a trustworthy activity descriptor. Promisingly, the η ORR values of Rh-C 7 N 3 , Ni-C 7 N 3 , and Pt-C 7 N 3 are 0.32, 0.38, and 0.44 V, respectively, even lower than the overpotential value of Pt(111). This suggests that these three catalysts demonstrate superior catalytic activity compared to Pt(111). [Display omitted] [ABSTRACT FROM AUTHOR]

Using quantum coherence effects, we have developed a new technique of detection of motion of single atoms or ions in an optical cavity. We have theoretically demonstrated that the presence of a single atom or ion inside cavity leads to a shift in cavity frequency and phase of transmitted probe beams. It has been shown by the use of EIT technique, the change of the phase is extremely sensitive to probe detuning in the vicinity of resonance frequency and can be in the order of . [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A kind of low-cost and high-active single-atom HER electrocatalysts are investigated. • The 558 grain boundaries in graphene can be served as a substrate to support the transition metal atom. • The Fe, Co, Ni and V atom anchored on 558 GB can tune the free energy of hydrogen adsorption close to zero. Abstract Embedding a single atom into the supported catalysts is the most effective way to maximize the catalytic efficiency, holding promise for developing low-cost electrocatalysts. Grain boundaries in graphene display unique structures and have attracted great research efforts in electronic properties, catalysis and sensors. By using density function theory (DFT) calculations, we systematically investigated the potential of a single transition metal (TM) atom (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, Pt) supported on the experimentally realised 558 grain boundary (GB), as a highly efficient electrocatalyst for hydrogen evolution reaction (HER). We find that the Fe, Co, Ni and V atom anchored on 558 GB can substantially tune the free energy of hydrogen adsorption to a more optimal value, especially for the V atom (Δ G H ∗ = −0.01 eV), which is very close to, or even better than the most active Pt and MoS 2 catalysts. This feature is attributed to the charge transfer between TM atom and the adsorbed H atom, which significantly promotes the proton adsorption and the reduction of kinetics. In addition, a large number of electronic states near the Fermi level ensure efficient electron transfer. Our study may provide a new cost-effective, highly active and earth-abundant HER electrocatalyst for hydrogen production. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Charge carrier transfer in transition-metal single atom/g-C 3 N 4 is explored. • Fe, Co, Ni atoms act as bridge to promote g-C 3 N 4 interlayer charge transfer. • Internal electric field is formed in the single atom (Fe, Co)/g-C 3 N 4 model. Abstract The decoration by transition-metal single atoms shows great potential in enhancing the photocatalytic performance of semiconductors. Nevertheless, the factors accounting for this enhancement remain unknown. Herein, single atoms (Fe, Co, Ni, Cu, Zn) loaded g-C 3 N 4 were used as prototypes to investigate the mechanism through density functional theory (DFT). The results indicate that Fe, Co and Ni single atoms are inclined to penetrate into g-C 3 N 4 , prolonging the charge carrier migration distance. Furthermore, these single atoms can act as bridge to promote charge carrier transfer across g-C 3 N 4 interlamination through the reconstitution of molecular orbitals. Among these five metals, built-in electric field is created in Fe/g-C 3 N 4 and Co/g-C 3 N 4 models, effectively suppressing the recombination of electron–hole pairs. In contrast, Cu and Zn atoms can only be loaded on the g-C 3 N 4 surface, contributing trivial to the interlayer charge carrier migration. Our work provides theoretical support for the study of transition-metal single atom/g-C 3 N 4 systems and gives new insight into the photocatalytic performance enhancement. [ABSTRACT FROM AUTHOR]

Mercury (Hg) pollution caused by coal-fired power plants has raised global concerns, and it is imperative for developing a new low cost technology to control Hg emissions. Single atom iron catalyst with graphene-based substrates (Fe/GS) which has high catalytic activity and high selectivity is a promising material for removal of mercury pollution. The adsorption characteristics of mercury species on single atom iron catalysts with different graphene-based substrates were investigated systematically using first-principles calculation. It is found that the support effects of graphene-based substrates have a significant influence on adsorption characteristic of mercury species, and the support effects can be well understood through electronic structure analysis. Fermi softness is a good descriptor for adsorption activity of Fe/GS which can be an indicator for design and optimization of new materials. Fe/GS may be a new material for removal of Hg 0 pollutant, and the temperature has an inhibitory effect on mercury species adsorption. Furthermore, the findings can provide a novel perspective for adsorption and oxidation of Hg and lay a foundation for the further study of graphene-based support effects in single atom catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FECO) up to 95 % at −0.43 V), remarkable durability (>75 h without decay of FECO), and large turnover frequency (TOF, up to 9969 h−1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N4) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step. [ABSTRACT FROM AUTHOR]

The article offers information on coherent perfect absorption, which is the complete extinction of incoming radiation by a complex potential in a physical system supporting wave propagation. It mentions that this concept was proven for linear waves in a variety of systems including light interacting with absorbing scatterers, plasmonic metasurfaces, and graphene films; and it opens perspectives for designing atom lasers.

Abstract: Two Pt single‐atom catalysts (SACs) of Pt‐GDY1 and Pt‐GDY2 were prepared on graphdiyne (GDY)supports. The isolated Pt atoms are dispersed on GDY through the coordination interactions between Pt atoms and alkynyl C atoms in GDY, with the formation of five‐coordinated C1‐Pt‐Cl4 species in Pt‐GDY1 and four‐coordinated C2‐Pt‐Cl2 species in Pt‐GDY2. Pt‐GDY2 shows exceptionally high catalytic activity for the hydrogen evolution reaction (HER), with a mass activity up to 3.3 and 26.9 times more active than Pt‐GDY1 and the state‐of‐the‐art commercial Pt/C catalysts, respectively. Pt‐GDY2 possesses higher total unoccupied density of states of Pt 5d orbital and close to zero value of Gibbs free energy of the hydrogen adsorption (|Δ G Pt H * |) at the Pt active sites, which are responsible for its excellent catalytic performance. This work can help better understand the structure–catalytic activity relationship in Pt SACs. [ABSTRACT FROM AUTHOR]

The maximized atomic efficiency of supported catalysts is highly desired in heterogeneous catalysis. Therefore, the design and development of active, stable, and atomic metal-based catalysts remains a formidable challenge. To tackle these problems, it is necessary to investigate the interaction between single atoms and supports. Theoretical calculations indicate that the Pd binding strength is higher on graphene/amorphous carbon (AC) than that on graphene or AC substrate. Based on these predictions, we present a facile confined-interface-directed synthesis route for the preparation of single-atom catalysts (SACs) in which Pd atoms are well-dispersed on the interface of double-shelled hollow carbon nanospheres with reduced graphene oxide (RGO) as the inner shell and AC as the outer shell. Owing to the synergetic effect of the RGO/AC confined interface and the atomically dispersed Pd, the as-made RGO@AC/Pd SAC achieves the maximum atomic efficiency (catalytic activity) of Pd species and exhibits an excellent stability in chemical catalysis. This confined-interface-directed synthesis method provides a novel direction to maximize the atomic efficiency, improve the activity, and enhance the stability of metal-based catalysts. [ABSTRACT FROM AUTHOR]

We investigate the strong coupling phenomenon in the structure of metallic nanoparticle partially buried in molecular J-aggregates. The wave vector and the polarization of incident light impact on the strong coupling phenomenon. With the wave vector and the polarization of incident light in the plane of the interface between the air and molecular J-aggregates, the detuning energies δ reach to the largest. Incident light being injected normally from the air to molecular J-aggregates or from molecular J-aggregates to the air does not influence on δ, but influences on the intensities of the scattering spectra. Our structure has a great help in fabricating the structure which is used to generate the strong coupling phenomenon and also has potential applications in quantum networks, single-atom lasers, quantum information processing, and so on. [ABSTRACT FROM AUTHOR]

The article focuses on the study of majorana bound states (MBS) in condensed matter systems which is an important challenge focused on topological quantumcomputing. It focuses on the novel approach to design model-type atomic-scale systems for studying MBS by using single-atom manipulation techniques.

Superradiance is a quantum phenomenon emerging in macroscopic systems whereby correlated single atoms cooperatively emit photons. Demonstration of controlled collective atom-field interactions has resulted from the ability to directly imprint correlations with an atomic ensemble. Here we report cavity-mediated coherent single-atom superradiance: Single atoms with predefined correlation traverse a high–quality factor cavity one by one, emitting photons cooperatively with the N atoms that have already gone through the cavity (N represents the number of atoms). Enhanced collective photoemission of N-squared dependence was observed even when the intracavity atom number was less than unity. The correlation among single atoms was achieved by nanometer-precision position control and phase-aligned state manipulation of atoms by using a nanohole-array aperture. Our results demonstrate a platform for phase-controlled atom-field interactions. [ABSTRACT FROM AUTHOR]

Conventionally, the singly occupied molecular orbital (SOMO) of a radical species is considered to be the highest occupied molecular orbital (HOMO), but this is not the case always. In this study, we considered a number of radicals from smallest diatomic anion radicals such as superoxide anion radical to one-electron oxidized DNA related base radicals that show the SOMO is energetically lower than one or more doubly occupied molecular orbitals (MOs) (SOMO-HOMO level inversion). The electronic configurations are calculated employing the B3LYP/6-31++G** method, with the inclusion of aqueous phase via the integral equation formalism of the polarized continuum model solvation model. From the extensive study of the electronic configurations of radicals produced by one-electron oxidation or reduction of natural-DNA bases, bromine-, sulfur-, selenium-, and aza-substituted DNA bases, as well as 20 diatomic molecules, we highlight the following important findings: (i) SOMO-HOMO level inversion is a common phenomenon in radical species. (ii) The more localized spin density in σ-orbital on a single atom (carbon, nitrogen, oxygen, sulfur, or selenium), the greater the gap between HOMO and SOMO. (iii) In species with SOMO-HOMO level inversion, one-electron oxidation takes place from HOMO not from the SOMO, which produces a molecule in its triplet ground state. Oxidation of aqueous superoxide anion producing triplet molecular oxygen is one example of many. (iv) These results are for conventional radicals and in contrast with those reported for distonic radical anions in which SOMO-HOMO gaps are smaller for more localized radicals and the orbital inversions vanish in water. Our findings yield new insights into the properties of free radical systems. [ABSTRACT FROM AUTHOR]

The mechanism for dimethyl carbonate (DMC) synthesis by oxidation carbonylation of methanol on a single-atom Cu 1 /graphene catalyst was investigated by density-functional theory calculations. Carbon vacancies in graphene can significantly enhance the interaction between Cu atoms and graphene supports, and provide an increased transfer of electrons from Cu atoms to the graphene sheet. Compared with Cu-doped divacancy graphene (Cu/DG), Cu-doped monovacancy graphene (Cu/MG) provides a stronger interaction between adsorbents and the catalyst surface. Among the reaction processes over Cu 1 /graphene catalysts, CO insertion into methoxide was more favorable than dimethoxide. The rate-limiting step on the Cu/DG surface is the carbomethoxide reaction with methoxide, which is exothermic by 164.6 kJ mol −1 and has an activation barrier of 190.9 kJ mol −1 energy. Compared with that on the Cu crystal surface, Cu 4 and Cu 3 Rh clusters, and the Cu 2 O(111) surface, the rate-determining step for DMC formation on Cu/MG, which is CO insertion into methoxide, needs to overcome the lowest barrier of 73.5 kJ mol −1 and is exothermic by 44.6 kJ mol −1 . Therefore, Cu/MG was beneficial to the formation of DMC as a single-atom catalyst. [ABSTRACT FROM AUTHOR]

Single atom imaging requires discrimination of weak photon count events above the background and has typically been performed using electron-multiplying charge-coupled device cameras, photomultiplier tubes, or single photon counting modules. A scientific complementary metal-oxide semiconductor (sCMOS) provides a cost effective and highly scalable alternative to other single atom imaging technologies, offering fast readout and larger sensor dimensions. We demonstrate single atom resolved imaging of two site-addressable optical traps separated by 10 μm using an sCMOS camera, offering a competitive signal-to-noise ratio at intermediate count rates to allow high fidelity readout discrimination (error<10-6) and sub-μm spatial resolution for applications in quantum technologies. [ABSTRACT FROM AUTHOR]

It has been shown that an optical trap for an atomic condensate formed by a mode of a ring cavity possesses specific properties. These properties are not featured by a trap formed by free beams and arise owing to quantum correlations (entanglement) between the localized atoms and the optical mode. In particular, there is an effect similar to an optomechanical phenomenon known as an 'optical spring' (S. Martellucci et al., Bose-Einstein Condensates and Atom Lasers (Kluwer, Dordrecht, 2002)) and manifested by the emergence of an effective correction to the interaction between the localized atoms. The magnitude and sign of this correction can be controlled by varying the frequency of the source forming the trap. [ABSTRACT FROM AUTHOR]

Recent advances in attosecond science in combination with the well-established techniques of nanofabrication have led to the new research field of attosecond nanophysics. One central goal is the characterization and manipulation of electromagnetic fields on the attosecond and nanometer scale. This has so far remained challenging both theoretically and experimentally. One major obstacle is the inhomogeneity of the electric fields. We present a general model below, which allows the description of attosecond streaking in near fields. It allows the classification into different regimes as well as the reconstruction of the electric fields at the surface. In addition, we discuss the case of parallel polarization of the streaking fields to the surface, which has so far not been considered for attosecond streaking from metallic surfaces. Finally, we review recent measurements of the electric field and response function of a gold nanotaper. Our results are highly relevant for future attosecond streaking experiments in inhomogeneous fields. [ABSTRACT FROM PUBLISHER]

We discuss a fundamentally new method for electric (E) field strength (V/m) metrology applicable to the near-field. This new approach is significantly different from currently used field measurement techniques in that it is based on the interaction of radio-frequency (RF) E-fields with Rydberg atoms (alkali atoms placed in a glass vapor cell that are excited optically to Rydberg states). The applied RF E-field alters the state of the atoms. The Rydberg atoms act like an RF-to-optical transducer, converting an RF E-field strength to an optical-frequency response. In this new approach, we employ the phenomena of electromagnetically induced transparency (EIT) and Autler-Townes splitting. The RF transition in the four-level atomic system causes a split of the EIT transmission spectrum of a probe laser into two peaks. This splitting is easily measured and is directly proportional to the applied RF E-field amplitude. The significant dipole response of Rydberg atoms enables this technique to make self-calibrating measurements over a large frequency band including 500 MHz to 500 GHz (and possibly up to 1 THz and down to 10s of megahertz). In this paper, we report on our results in the development of this metrology approach, including the first fiber-coupled vapor-cell for E-field measurements. We also discuss key applications, including self-calibrated measurements, millimeter-wave and sub-THz measurements, field mapping, and sub-wavelength and near-field imaging. We show results for mapping the fields inside vapor cells, for measuring the E-field distribution along the surface of a circuit board, and for measuring the near-field at the aperture in a cavity. We also discuss the uncertainties of this measurement technique. [ABSTRACT FROM PUBLISHER]

Preferential oxidation of CO (PROX) is an important reaction for removing CO to a parts-per-million level from the hydrogen-rich stream. Recent experimental results show single-atom alloys (SAAs) of Cu surfaces doped by transition-metal (TM) of group VIII (TM = Ni, Pd, Pt) exhibit excellent catalytic performance toward hydrogenation and a variety of oxidation reactions including PROX of CO. To unravel mechanism, we performed DFT calculations to investigate. Cu n Pt exhibited higher activity for both H 2 dissociation and the PROX when compared with Cu n Ni and Cu n Pd. Especially, Cu 6 Pt emerges as the best surface for both H 2 dissociation and the PROX. The investigation on catalytic mechanism, we first found the element step is the formation of hydroxyl and atomic oxygen simultaneously. This work provides insight into the Cu-TM SAA catalysts, which may give helpful information for design of Cu-based catalysts for industrially important PROX. [ABSTRACT FROM AUTHOR]

Conventional supported Pt for industrial catalytic reforming exhibits high conversion, but suffers low selectivity due to the hydrogenolysis reaction. The development of highly dispersed Pt offers the opportunity to settle this problem. Here, a supported Pt, with Pt dispersed in single atoms plus small clusters with fewer than 10 atoms (91%) on Sn-containing mixed metal oxides, has been prepared by the induction of a Sn component confined in the lattices of brucite-like layers of layered double hydroxides. Pt in single-atom and small-cluster dispersion effectively inhibits hydrogenolysis and significantly improves the selectivity to cyclization products in the n -heptane reforming reaction. [ABSTRACT FROM AUTHOR]

In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt fourcoordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt%) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities. [ABSTRACT FROM AUTHOR]

Y is a trivalent metal like Al but has one d valence electron instead of one p valence electron in Al. This makes a single-atom contact of Y a suitable playground for investigating how d valence electrons contribute to the single-atom conductance. In this paper, we present the results of our theoretical and experimental studies of the single-atom conductance of Y. We carried out conductance measurements on Y contacts and found that the conductance histogram observed at 4 K exhibits a single broad peak at 1.9 G 0 . We also calculated the electron transmission through a Y single-atom contact and obtained the total transmission 1.75 at the Fermi level. Both our theoretical and experimental findings consistently indicate that the single-atom conductance of Y lies at ( 1.8 – 1.9 ) G 0 , which is nearly twice as high as that of Al. This increase in the single-atom conductance is due to the second and the third eigenchannels of Y which accomplish higher transmission compared to those of Al. We found that the difference in the contours of sd - and sp -eigenchannels can account for the higher transmission of the sd -eigenchannels. [ABSTRACT FROM AUTHOR]

In this work, a transmission-type, low-kilovolt coherent electron diffractive imaging instrument was constructed. It comprised a single-atom field emitter, a triple-element electrostatic lens, a sample holder, and a retractable delay line detector to record the diffraction patterns at different positions behind the sample. It was designed to image materials thinner than 3 nm. The authors analyzed the asymmetric triple-element electrostatic lens for focusing the electron beams and achieved a focused beam spot of 87 nm on the sample plane at the electron energy of 2 kV. Highangle coherent diffraction patterns of a suspended graphene sample corresponding to (0.62Å)-1 were recorded. This work demonstrated the potential of coherent diffractive imaging of thin twodimensional materials, biological molecules, and nano-objects at a voltage between 1 and 10 kV. The ultimate goal of this instrument is to achieve atomic resolution of these materials with high contrast and little radiation damage. [ABSTRACT FROM AUTHOR]

Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations, the potential of graphyne as substrate materials for noble-metal (Au, Pt, Ir, Pd, Rh, and Ru) single-atom catalysts have been systematically investigated. It is found that the adsorption of most considered noble-metal single atoms is very strong at the hollow site above the center of the acetylenic ring of the graphyne sheet and their diffusion away from this site towards its neighboring sites is rather difficult, which makes it highly possible to realize well-ordered and uniformly distributed noble-metal single-atom catalysts on graphyne. Furthermore, the catalytic activity of the Ru-decorated graphyne was investigated by using CO oxidation as a probe. The calculated low energy barrier for the reaction suggests that the Ru-decorated graphyne is a viable catalyst for CO oxidation at low temperature. Based on electronic structure analyses, the high catalytic activity of this system is attributed to the charge transfer and the orbital hybridization between the adsorbates and the Ru atom. This study suggests that graphyne sheets are promising substrates for the synthesis of the noble-metal single-atom catalysts. [ABSTRACT FROM AUTHOR]

Magnetism of Mn single atom and dimer on Co(0001) hcp surface is studied on the basis of density functional theory using Quantum Espresso code. The most stable geometry takes place when Mn is adsorbed in the most highly coordinated sites. Mn single atom couples ferromagnetically to the Co atoms and shows a high magnetic moment of 4.53 μ B . Mn dimer also couples ferromagnetically to the Co atoms, shows a mean atomic magnetic moment of 4.45 μ B , and increases its interatomic distance to minimize its energy. [ABSTRACT FROM AUTHOR]

We predict a bistability in the photon emission from a solid-state single-atom laser comprising a microwave cavity coupled to a voltage-biased double quantum dot. To demonstrate that the single-atom laser is bistable, we evaluate the photon emission statistics and show that the distribution takes the shape of a tilted ellipse. The switching rates of the bistability can be extracted from the electrical current and the shot noise in the quantum dots. This provides a means to control the photon emission statistics by modulating the electronic transport in the quantum dots. Our prediction is robust against moderate electronic decoherence and dephasing and is important for current efforts to realize single-atom lasers with gatedefined quantum dots as the gain medium. [ABSTRACT FROM AUTHOR]

We consider quasi-stationary scattering of interacting bosonic matter waves in one-dimensional waveguides, as they arise in guided atom lasers. We show how the truncated Wigner (tW) method, which corresponds to the semiclassical description of the bosonic many-body system on the level of the diagonal approximation, can be utilized in order to describe such many-body bosonic scattering processes. Special emphasis is put on the discretization of space at the exact quantum level, in order to properly implement the semiclassical approximation and the tW method, as well as on the discussion of the results to be obtained in the continuous limit. [ABSTRACT FROM AUTHOR]

Resonance enhancement of high-order harmonic generation has recently been found in the interaction of intense ultrashort laser pulses with laser ablated plasma plumes. It is a promising route towards the production of an intense and coherent extreme ultraviolet radiation source. However, the mechanism of this resonance enhancement is still not clear. There are two possible explanations; one relies on a better recombination cross section through an autoionization state in the single-atom response. The other relies on improved phase matching conditions around the resonance. Here, we try to discriminate between these two conjectures by measuring coherence lengths of the harmonics, both on resonance and off resonance. Our findings support the single-atom response hypothesis. [ABSTRACT FROM AUTHOR]

The observation of sharp atomiclike multiplet features is unexpected for individual 3d atoms adsorbed on transition-metal surfaces. However, we show by means of x-ray absorption spectroscopy and x-ray magnetic circular dichroism that individual Fe atoms on Cu(111) exhibit such features. They are reminiscent of a low degree of hybridization, similar to 3d atoms adsorbed on alkali-metal surfaces. We determine the spin, orbital, and total magnetic moments, as well as magnetic anisotropy energy for the individual Fe atoms and for small Fe clusters that we form by increasing the coverage. The multiplet features are smoothened and the orbital moment rapidly decreases with increasing cluster size. For Fe monomers, comparison with density functional theory and multiplet calculations reveals a d7 electronic configuration, owing to the transfer of one electron from the 4s to the 3d states. [ABSTRACT FROM AUTHOR]

We study the tunneling dynamics of bosons with periodically modulated interaction held in a triple-well potential. In high-frequency approximation, we derive a set of reduced coupled equations and the corresponding Floquet solutions are obtained. Based on the analytical results and their numerical correspondence, the directed selective-tunneling effect of a single atom is demonstrated when all bosons are prepared in middle well initially. A scheme for separating a single atom from N bosons is presented, in which the atom can be trapped in right or left well by adjusting the modulation strength. [ABSTRACT FROM AUTHOR]

This study identifies a procedure for the calibration of the Z-magnification of an atomic force microscope below 10 nm by single-atom steps and gives an uncertainty evaluation. A Si(111) surface with periodically arranged single-atom steps was used as a standard reference. The lattice constant of the Si(111) is 0.312 nm, which is traced to SI units through X-ray diffraction. The 33 layers of continuous stacked single-atom steps were scanned and step heights ranging from 0.3 nm to 10 nm were measured and analyzed. The influential factors of calibration for the Z-magnification of an atomic force microscope were identified to estimate the uncertainty according to ISO/IEC Guide 98-3:2008. The relative expanded uncertainties ranged from 4.7% to 5.9%. [ABSTRACT FROM AUTHOR]

A phase reconstruction method based on multiple scanning transmission electron microscope (STEM) images was evaluated quantitatively using image simulations. The simulation results indicated that the phase shift caused by a single atom was proportional to the 0.6th power of the atomic number Z. For a thin SrTiO3 [001] crystal, the reconstructed phase at each atomic column increased according to the specimen thickness. The STEM phase images can quantify the oxygen vacancy concentration if the thickness is less than several nanometers. [ABSTRACT FROM AUTHOR]