Quantum phases of dipolar bosons in optical lattices

The ground state of dipolar bosons placed in an optical lattice is analyzed. We show that the modification of experimentally accessible parameters can lead to the realization and control of different quantum phases, including superfluid, supersolid, Mott insulator, checkerboard, and collapse phases.     

Entanglement as a precondition for secure quantum key distribution

We demonstrate that a necessary precondition for an unconditionally secure quantum key distribution is that both sender and receiver can use the available measurement results to prove the presence of entanglement in a quantum state that is effectively distributed between them. One can thus systematically search for entanglement using the class of entanglement witness operators that can be constructed from the observed data. We apply such analysis to two well-known quantum key distribution protocols, namely, the 4-state protocol and the 6-state protocol. As a special case, we show that, for some asymmetric error patterns, the presence of entanglement can be proven even for error rates above 25% (4-state protocol) and 33% (6-state protocol).     

Coherence properties of guided-atom interferometers

We present a detailed theoretical investigation of the coherence properties of beam splitters and Mach-Zehnder interferometers for guided neutral atoms. We show that such a setup permits coherent wave packet splitting and leads to the appearance of interference fringes for both single-mode and thermal input states, evidencing thus the robustness of the interferometer.     

Experimental detection of multipartite entanglement using witness operators

We present the experimental detection of genuine multipartite entanglement using entanglement witness operators. To this aim, we introduce a canonical way of constructing and decomposing witness operators so that they can be directly implemented with present technology. We apply this method to three- and four-qubit entangled states of polarized photons, giving experimental evidence that the considered states contain true multipartite entanglement.     

Entanglement in spin chains and lattices with long-range Ising-type interactions

We consider N initially disentangled spins, embedded in a ring or d-dimensional lattice of arbitrary geometry, which interact via some long-range Ising-type interaction. We investigate relations between entanglement properties of the resulting states and the distance dependence of the interaction in the limit N-->infinity. We provide a sufficient condition when bipartite entanglement between blocks of L neighboring spins and the remaining system saturates and determine S(L) analytically for special configurations. We find an unbounded increase of S(L) as well as diverging correlation and entanglement length under certain circumstances. For arbitrarily large N, we can efficiently calculate all quantities associated with reduced density operators of up to ten particles.     

Fractional quantum Hall states in ultracold rapidly rotating dipolar fermi gases

We demonstrate the experimental feasibility of incompressible fractional quantum Hall-like states in ultracold two-dimensional rapidly rotating dipolar Fermi gases. In particular, we argue that the state of the system at filling fraction nu = 1/3 is well described by the Laughlin wave function and find a substantial energy gap in the quasiparticle excitation spectrum. Dipolar gases, therefore, appear as natural candidates of systems that allow us to realize these very interesting highly correlated states in future experiments.     

Proximal regioselectivity of the O,O'-dialkylation of tetrahydroxyketocalix[4]arene

The only dialkylated products obtained in the reaction of tetrahydroxyketocalixarene 2a with MeI/K(2)CO(3) or PhCH(2)Br/K(2)CO(3) are the corresponding proximal (i.e., 1,2) O,O'-dialkyl ethers, in contrast to the parent tetrahydroxycalix[4]arene 1a which affords the distal (1,3) dialkyl ether derivatives. Pairs of geminally alkylated phenoxy groups in the conformationally rigid dibenzylated and tetrabenzylated derivatives are oriented in an anti fashion. These results can be rationalized assuming that the 1,3-alternate arrangement of the rings preferred by 2a is adopted during all the intermediate stages of the alkylation. The NMR spectra (in CDCl(3)) of the monomethyl, dimethyl, trimethyl, and tetramethyl ether derivatives of 2a are in agreement with a 1,3-alternate conformation.     

Bound entanglement and continuous variables

We introduce the definition of generic bound entanglement for the case of continuous variables. We provide some examples of bound entangled states for that case, and discuss their physical sense in the context of quantum optics. We raise the question of whether the entanglement of these states is generic. As a by-product we obtain a new many parameter family of bound entangled states with positive partial transpose. We also point out that the "entanglement witnesses" and positive maps revealing the corresponding bound entanglement can easily be constructed.     

Liquid chromatographic determination of multiple sulfonamides, nitrofurans, and chloramphenicol residues in pasteurized milk

A rapid and selective liquid chromatographic method was developed to detect 6 sulfonamides, 3 nitrofurans, and chloramphenicol residues in pasteurized milk. The 10 drugs were extracted with chloroform-acetone and the organic phase was evaporated; the residues were dissolved in an aqueous sodium acetate buffer solution 0.02M (pH = 4.8), and the fat was removed by washing with hexane. The aqueous layer was collected, filtered, and injected. The 6 sulfonamides and chloramphenicol were detected at 275 nm ultraviolet (UV) using a gradient system starting with sodium acetate buffer solution-acetonitrile (95 + 5) and finishing with sodium acetate buffer solution-acetonitrile (80 + 20). Nitrofurans were detected at 375 nm (UV) isocratically with sodium acetate buffer solution-acetonitrile (80 + 20). For 50 ppb fortified milk, the average recoveries were (sulfathiazole) 65.52%; (sulfamerazine) 75.36%; (sulfamethazine) 93.94%; (sulfachlorpyridazine) 75.94%; (sulfamethoxazole) 85.18%; (sulfamonomethoxine) 83.45%; (chloramphenicol) 104.17%; (nitrofurazone) 91.81%; (furazolidone) 100.76%; and (furaltadone) 72.38%. Method detection limits ranged from 4 ppb (nitrofurazone) to 16 ppb (sulfamethazine). Some matrix interferences (3-7 ppb) were observed only with sulfonamides.     

Ozonolysis of 1,4-cyclohexadienes in the presence of methanol and acid. Mechanism and intermediates in the conversion of 1,4-cyclohexadiene derivatives to beta-keto esters

Conditions for the preparation of beta-keto esters directly from 1,4-cyclohexadiene derivatives are described. This procedure is a further step in the application of the synthetic methodology, which consists of the combination of Birch reduction of available benzene derivatives followed by ozonolysis. In this work, the syntheses of derivatives of dimethyl gamma-keto-alpha-aminoadipate and dimethyl beta-keto glutamate from the corresponding 1,4-cyclohexadiene derivatives are described. The latter compounds are prepared from phenylalanine and phenylglycine, respectively. The study of the ozonolysis of simple alkyl derivatives of 1,4-cyclohexadiene in the presence of methanol, both in the presence and absence of acid, helped to establish the mechanism of this reaction. The proximity of the two double bonds, which are cleaved, leads to the intermediate formation of 1,2-dioxolane derivatives that could be identified by NMR spectroscopy. It is shown that regardless of the regioselectivity of the cleavage of the primary ozonide, which is formed, all 1,2-dioxolane derivatives can lead to beta-keto esters. This is due to the equilibrium between these dioxolanes in the presence of methanol and acid.