Control and Entanglement of Individual Rydberg Atoms near a Nanoscale Device.

Coherent control of Rydberg atoms near dielectric surfaces is a major challenge due to the large sensitivity of Rydberg states to electric fields. We demonstrate coherent single-atom operations and two-qubit entanglement as close as 100 µm from a nanophotonic device. Using the individual atom control enabled by optical tweezers to study the spatial and temporal properties of the electric field from the surface, we employ dynamical decoupling techniques to characterize and cancel the electric-field noise with submicrosecond temporal resolution. We further use entanglement-assisted sensing to accurately map magnitude and direction of electric-field gradients on a micrometer scale. Our observations open a path for integration of Rydberg arrays with micro- and nanoscale devices for applications in quantum networking and quantum information science.

Investigation of Calcium Forms in Lichens from Travertine Sites.

Lichens are symbiotic organisms with an extraordinary capability to colonise areas of extreme climate and heavily contaminated sites, such as metal-rich habitats. Lichens have developed several mechanisms to overcome the toxicity of metals, including the ability to bind metal cations to extracellular sites of symbiotic partners and to subsequently form oxalates. Calcium is an essential alkaline earth element that is important in various cell processes. Calcium can serve as a metal ligand but can be toxic at elevated concentrations. This study investigated calcium-rich and calcium-poor sites and the lichen species that inhabit them (Cladonia sp.). The calcium content of these lichen species were analyzed, along with localized calcium oxalate formed in thalli collected from each site. The highest concentration of calcium was found in the lichen squamules, which can serve as a final deposit for detoxification. Interestingly, the highest content of calcium in Cladonia furcata was localized to the upper part of the thallus, which is the youngest. The produced calcium oxalates were species-specific. Whewellite (CaC2O4∙H2O) was formed in the case of C. furcata and weddellite (CaC2O4∙2H2O) was identified in C. foliacea.

Entanglement transport and a nanophotonic interface for atoms in optical tweezers.

The realization of an efficient quantum optical interface for multi-qubit systems is an outstanding challenge in science and engineering. Using two atoms in individually controlled optical tweezers coupled to a nanofabricated photonic crystal cavity, we demonstrate entanglement generation, fast nondestructive readout, and full quantum control of atomic qubits. The entangled state is verified in free space after being transported away from the cavity by encoding the qubits into long-lived states and using dynamical decoupling. Our approach bridges quantum operations at an optical link and in free space with a coherent one-way transport, potentially enabling an integrated optical interface for atomic quantum processors.

Strong Coupling of Two Individually Controlled Atoms via a Nanophotonic Cavity.

We demonstrate photon-mediated interactions between two individually trapped atoms coupled to a nanophotonic cavity. Specifically, we observe collective enhancement when the atoms are resonant with the cavity and level repulsion when the cavity is coupled to the atoms in the dispersive regime. Our approach makes use of individual control over the internal states of the atoms and their position with respect to the cavity mode, as well as the light shifts to tune atomic transitions individually, allowing us to directly observe the anticrossing of the bright and dark two-atom states. These observations open the door for realizing quantum networks and studying quantum many-body physics based on atom arrays coupled to nanophotonic devices.

Geochemical distribution of selected elements in flotation tailings and soils/sediments from the dam spill at the abandoned antimony mine Stolice, Serbia.

Materials held within mine tailings pose a serious risk to the environment in cases of tailings dam failure. Collapse of the tailing dam at the Stolice antimony mine in West Serbia caused a spilling of tailing slurry into the nearby river watersheds. Medium-term effects of As, Pb, Sb, Zn, and Cd from the tailings material that remained in the flooded zone 3 years after the initial exposure were evaluated. Mobility of these elements was determined by analyzing their distribution between exchangeable, reducible, oxidizable, and residual phases. Results indicate that Fe-Mn oxides represent important sinks for As, Cd, Pb, and Sb. Multivariate statistical analysis revealed that concentrations of the analyzed elements were related to sand-sized fractions, as they tended to adsorb or co-precipitate as coatings on larger particles (particularly feldspar and quartz) upon the change of redox conditions. Assessment of the most relevant physico-chemical factors, metal(loid) concentration, and mobility can be used as tool to characterize the degree of contamination of impacted sites. Percentage of sand-sized particles, content of investigated metal(loid)s, and their amount in the reducible fractions are factors determining the best remediation techniques for the area impacted by tailing spill.

Crystal structure of the tetra-gonal polymorph of bis-(1-ethyl-3-methyl-imidazolium) tetra-bromido-cadmate.

Both unique Cd atoms in the tetra-gonal polymorph of bis-(1-ethyl-3-methyl-imidazolium) tetra-bromido-cadmate, (C6H11N2)2[CdBr4], occupy special positions (site symmetry -4). The crystal structure consists of isolated tetra-hedral [CdBr4](2-) anions which are surrounded by 1-ethyl-3-methyl-imidazolium cations. The methyl and ethyl side chains of the cations show positional disorder in a 0.590 (11):0.410 (11) ratio. In the crystal, (C6H11N2)(+) cations display three weak C-H⋯Br hydrogen-bond inter-actions through the imidazolium ring H atoms with the Br(-) ligands of the surrounding complex anions. The alkyl groups of the side chains are not involved in hydrogen bonding.

Simple method for locking birefringent resonators.

We report on a simple method of locking a laser to a birefringent cavity using polarization spectroscopy. The birefringence of the resonator permits the simple extraction of an error signal by using one polarization state as a phase reference for another state. No modulation of the light or the resonator is required, reducing the complexity of the laser locking setup. This method of producing an error signal can be used on most birefringent optical resonators, even if the details of birefringence and eigenpolarizations are not known. This technique is particularly well suited for fiber ring resonators due to the inherent birefringence of the fiber and the unknown nature of that birefringence. We present an experimental demonstration of this technique using a fiber ring.

An investigation of polyhedral deformation in two mixed-metal diarsenates: SrZnAs2O7 and BaCuAs2O7.

Two isostructural diarsenates, SrZnAs2O7 (strontium zinc diarsenate), (I), and BaCuAs2O7 [barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The three-dimensional open-framework crystal structure consists of corner-sharing M2O5 (M2 = Zn or Cu) square pyramids and diarsenate (As2O7) groups. Each As2O7 group shares its five corners with five different M2O5 square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine-coordinated M1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of the M1O9, M2O5 and As2O7 groups of known isostructural diarsenates, adopting the general formula M1(II)M2(II)As2O7 (M1(II) = Sr, Ba, Pb; M2(II) = Mg, Co, Cu, Zn) and crystallizing in the space group P21/n, are presented and discussed.

Ionothermal synthesis and crystal structure of a new organic-inorganic hybrid compound: catena-poly[bis(1-ethyl-3-methylimidazolium) [hepta-µ-bromido-pentacuprate(I)]].

A new organic-inorganic hybrid compound, catena-poly[bis(1-ethyl-3-methylimidazolium) [µ5-bromido-tri-µ3-bromido-tri-µ2-bromido-pentacuprate(I)]], {(C6H11N2)2[Cu5Br7]}n, has been obtained under ionothermal conditions from a reaction mixture containing Ba(OH)2·8H2O, Cu(OH)2·2H2O, As2O5, 1-ethyl-3-methylimidazolium bromide and distilled water. The crystal structure consists of complex [Cu5Br7](2-) anions arranged in sinusoidal {[Cu5Br7](2-)}n chains running along the a axis, which are surrounded by 1-ethyl-3-methylimidazolium cations. Three of the five unique Br atoms and one of the three Cu(I) atoms occupy special positions with half-occupancy (a mirror plane perpendicular to the b axis, site symmetry m). The Cu(I) ions are in a distorted tetrahedral coordination environment, with four Br atoms at distances ranging from 2.3667 (10) to 2.6197 (13) Å, and an outlier at 3.0283 (12) Å, exceptionally elongated and with a small contribution to the bond-valence sum of only 6.7%. Short C-H···Br contacts build up a three-dimensional network. The Cu···Cu distances within the chain range from 2.8390 (12) to 3.0805 (17) Å, indicating the existence of weak Cu(I)···Cu(I) cuprophilic interactions.

Ba[Co3(VO4)2(OH)2] with a regular Kagomé lattice.

The new layered title compound, barium di-µ-hydroxido-di-µ-vanadato-tricobaltate(II), was prepared under low-temperature hydrothermal conditions. Its crystal structure comprises Co(2+) and O(2-) ions in the Kagomé geometry. The octahedral Co(3)O(6)(OH)(2) Kagomé layers, made up of edge-shared CoO(4)(OH)(2) octahedra with Co on a site of 2/m symmetry, alternate along the c axis with barium vanadate heteropolyhedral layers, in which Ba is on a site of 3m symmetry and V is on a site of 3m symmetry. All three O atoms and the H atom also occupy special positions: two O atoms and the H atom are on sites with 3m symmetry and one O atom is on a site with m symmetry. Ba[Co(3)(VO(4))(2)(OH)(2)] represents the first compound from the four-component BaO-CoO-V(2)O(5)-H(2)O system and its structure is topologically related to the minerals vesignieite, Ba[Cu(3)(VO(4))(2)(OH)(2)], and bayldonite, Pb[Cu(3)(AsO(4))(2)(OH)(2)].

Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5.

Two new compounds, Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 (1) and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5 (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O4(OH0.5)2, M1aO4(OH0.5)2, M2O5(OH0.5), and M2aO5(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)0.5(AsO3(OH))0.5]2.5- and [(AsO4)0.5(AsO2(OH)2)0.5]2- tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of OH groups. The infrared spectra clearly show the presence of broad O-H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm-1 in (1), and 3210, 2379 1602 and 1310 cm-1 in (2). The O-H stretching frequency is in good agreement with O⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.

[Zn3(PO4)2(H2O)(0.8)(NH3)(1.2)].

The structure of the title compound, ammineaquadi-mu(5)-phosphato-trizinc(II), [Zn(3)(PO(4))(2)(H(2)O)(0.8)(NH(3))(1.2)], consists of two parts: (i) PO(4) and ZnO(4) vertex-sharing tetrahedra arranged in layers parallel to (100) and (ii) ZnO(2)(N/O)(2) tetrahedra located between the layers. Elemental analysis establishes the ammine-to-water ratio as 3:2. ZnO(2)(N/O)(2) tetrahedra are located at special position 4e (site symmetry 2) in C2/c. The two O atoms of ZnO(2)(N/O)(2) are bonded to neighbouring P atoms, forming two Zn-O-P linkages and connecting ZnO(2)(N/O)(2) tetrahedra with two adjacent bc plane layers. A noteworthy feature of the structure is the presence of NH(3) and H(2)O at the same crystallographic position and, consequently, qualitative changes in the pattern of hydrogen bonding and weaker N/O-H...O electrostatic interactions, as compared to two closely related structures.

Substitutional and positional disorder in Sr(2.88)Cu(3.12)(PO4)4.

The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr(3)Cu(3)(PO(4))(4), obtained previously by solid-state reaction, but not with Sr(3)Cu(3)(PO(4))(4), obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy-dispersive X-ray diffraction) analysis. The structure consists of layers of Cu(3)O(12) groups which are linked via the PO(4) tetrahedra. The Cu(3)O(12) groups are formed by one Cu1O(4) and two Cu2O(5) coordination polyhedra sharing corners. The central Cu1 atom of the Cu(3)O(12) group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry 1). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) A along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds.

Zn(1.86)Cd(0.14)(OH)VO(4).

The title compound, dizinc cadmium hydroxide tetraoxido-vanadate, Zn(1.86)Cd(0.14)(OH)VO(4), was prepared under low-temperature hydro-thermal conditions. It is isostructural with Zn(2)(OH)VO(4) and Cu(2)(OH)VO(4). In the crystal structure, chains of edge-sharing [ZnO(6)] octahedra are inter-connected by VO(4) tetra-hedra (site symmetries of both V atoms and their coordination polyhedra are .m.) to form a three-dimensional [Zn(OH)VO(4)](2-) framework with channels occupied by Zn and Zn/Cd cations adopting trigonal-bipyramidal and distorted octa-hedral coordinations, respectively. Zn(1.86)Cd(0.14)(OH)VO(4) is topologically related to adamite-type phases, and descloizite- and tsumcorite-type structures.

Sr, Ba and Cd arsenates with the apatite-type structure.

X-ray diffraction analysis of single crystals of three new arsenates adopting apatite-type structures yielded formula Sr(5)(AsO(4))(3)F for strontium arsenate fluoride, (I), (Sr(1.66)Ba(0.34))(Ba(2.61)Sr(0.39))(AsO(4))(3)Cl for strontium barium arsenate chloride, (II), and Cd(5)(AsO(4))(3)Cl(0.58)(OH)(0.42) for cadmium arsenate hydroxide chloride, (III). All three structures are built up of isolated slightly distorted AsO(4) tetrahedra that are bridged by Sr(2+) in (I), by Sr(2+)/Ba(2+) in (II) and by Cd(2+) in (III). Compounds (I) and (II) represent typical fluorapatites and chlorapatites, respectively, with F(-) at the 2a (0, 0, {1/4}) site and Cl(-) at the 2b (0, 0, 0) site of P6(3)/m. In contrast, in (III), due to the requirement that the smaller Cd(2+) cation is positioned closer to the channel Cl(-) anion (partially substituted by OH(-)), the anion occupies the unusual 2a (0, 0, {1/4}) site. Therefore, Cl(-) is similar to F(-) in (I), coordinated by three A2 cations, unlike the octahedrally coordinated Cl(-) in (II) and other ordinary chlorapatites. Furthermore, in (III), using FT-IR studies, we have inferred the existence of H(+) outside the channel in oxyhydroxyapatites and provided possible atomic coordinates for a H atom in HAsO(4)(2-), leading to a proposed formulation of the compound as Cd(5)(AsO(4))(3-x)(HAsO(4))(x)Cl(0.58)(OH)(0.42-x-(y/2))O(x+(y/2))(y/2).

Barium zinc diarsenate.

The title compound, BaZnAs(2)O(7), belongs to the family of isotypic series of compounds adopting the general formula M1(2+)M2(2+)X(2)O(7) (M1(2+) = Ca, Sr, Ba or Pb; M2(2+) = Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn or Cd; X = P or As). Suitable single crystals were prepared under hydro-thermal conditions. The framework structure is characterized by corner-sharing ZnO(5) square pyramids and As(2)O(7) groups where the Zn atoms occupy channels. X-ray diffraction analysis of single crystals twinned by non-merohedry [twin plane is (100)] yielded formula BaZnAs(2)O(7). Raman spectra confirmed the presence of a non-linear As-O-As linkage.

BaCo(2)(AsO(4))(2).

Suitable single crystals of the title compound, barium dicobalt(II) bis-[orthoarsenate(V)], were prepared under hydro-thermal conditions. This phase belongs to a series of compounds with general formula AM(2)(XO(4))(2), where A = alkaline earth metal, M = Mg or a divalent first-row transition element, and X = P, As or V. BaCo(2)(AsO(4))(2) is isotypic with BaNi(2)(XO(4))(2) (X = P, V or As) and is characterized by brucite-like sheets of edge-sharing CoO(6) octa-hedra (3 symmetry) parallel to (001), with one-third of the octa-hedral positions being vacant. The sheets are capped above and below by AsO(4) tetra-hedra (3 symmetry) and are inter-connected by distorted BaO(12) cubocta-hedra ( symmetry).