Continuous variable quantum teleportation with sculptured and noisy non-Gaussian resources

We investigate continuous variable (CV) quantum teleportation using relevant classes of non-Gaussian states of the radiation field as entangled resources. First, we introduce the class two-mode squeezed symmetric superposition of Fock states, including finite truncations of twin-beam Gaussian states as special realizations. These states depend on a set of free independent parameters that can be adjusted for the optimization of teleportation protocols, with an enhancement of the success probability of teleportation both for coherent and Fock input states. We show that the optimization procedure reduces the entangled resources to truncated twin beam states, which thus represents an optimal class of non-Gaussian resources for quantum teleportation. We then introduce a further class of two-mode non-Gaussian entangled resources, in the form of squeezed cat-like states. We analyze the performance and the properties of such states when optimized for (CV) teleportation, and compare them to the optimized squeezed Bell-like states introduced in a previous work \cite{CVTelepNoi}. We discuss how optimal resources for teleportation are characterized by a suitable balance of entanglement content and squeezed vacuum affinity. We finally investigate the effects of thermal noise on the efficiency of quantum teleportation. To this aim, a convenient framework is to describe noisy entangled resources as linear superpositions of non-Gaussian state and thermal states. Although the presence of the thermal component strongly reduces the teleportation fidelity, noisy non-Gaussian states remain preferred resources when compared to noisy twin-beam Gaussian states.Comment: 11 pages, 8 figures. Largely revised and expanded version. New material and sections added. To appear in EPJ-ST (Proceedings of the Central European Workshop on Quantum Optics 2007. 14th Edition, 1-5 June 2007, Palermo, Italy

Continuous variable quantum teleportation with non-Gaussian resources

We investigate continuous variable quantum teleportation using non-Gaussian states of the radiation field as entangled resources. We compare the performance of different classes of degaussified resources, including two-mode photon-added and two-mode photon-subtracted squeezed states. We then introduce a class of two-mode squeezed Bell-like states with one-parameter dependence for optimization. These states interpolate between and include as subcases different classes of degaussified resources. We show that optimized squeezed Bell-like resources yield a remarkable improvement in the fidelity of teleportation both for coherent and nonclassical input states. The investigation reveals that the optimal non-Gaussian resources for continuous variable teleportation are those that most closely realize the simultaneous maximization of the content of entanglement, the degree of affinity with the two-mode squeezed vacuum and the, suitably measured, amount of non-Gaussianity.Comment: 12 pages, 12 figure

Optimization of the transmission of observable expectation values and observable statistics in Continuous Variable Teleportation

We analyze the statistics of observables in continuous variable quantum teleportation in the formalism of the characteristic function. We derive expressions for average values of output state observables in particular cumulants which are additive in terms of the input state and the resource of teleportation. Working with Squeezed Bell-like states, which may be optimized in a free parameter for better teleportation performance we discuss the relation between resources optimal for fidelity and for different observable averages. We obtain the values of the free parameter which optimize the central momenta and cumulants up to fourth order. For the cumulants the distortion between in and out states due to teleportation depends only on the resource. We obtain optimal parameters for the second and fourth order cumulants which do not depend on the squeezing of the resource. The second order central momenta which is equal to the second order cumulants and the photon number average are optimized by the same resource. We show that the optimal fidelity resource, found in reference (Phys. Rev. A {\bf 76}, 022301 (2007)) to depend also on the characteristics of input, tends for high squeezing to the resource which optimizes the second order momenta. A similar behavior is obtained for the resource which optimizes the photon statistics which is treated here using the sum of the squared differences in photon probabilities of input and output states as the distortion measure. This is interpreted to mean that the distortions associated to second order momenta dominates the behavior of the output state for large squeezing of the resource. Optimal fidelity and optimal photon statistics resources are compared and is shown that for mixtures of Fock states they are equivalent.Comment: 25 pages, 11 figure

Measurements of the Yield Stress in Frictionless Granular Systems

We perform extensive molecular dynamics simulations of 2D frictionless granular materials to determine whether these systems can be characterized by a single static yield shear stress. We consider boundary-driven planar shear at constant volume and either constant shear force or constant shear velocity. Under steady flow conditions, these two ensembles give similar results for the average shear stress versus shear velocity. However, near jamming it is possible that the shear stress required to initiate shear flow can differ substantially from the shear stress required to maintain flow. We perform several measurements of the shear stress near the initiation and cessation of flow. At fixed shear velocity, we measure the average shear stress $\Sigma_{yv}$ in the limit of zero shear velocity. At fixed shear force, we measure the minimum shear stress $\Sigma_{yf}$ required to maintain steady flow at long times. We find that in finite-size systems $\Sigma_{yf} > \Sigma_{yv}$, which implies that there is a jump discontinuity in the shear velocity from zero to a finite value when these systems begin flowing at constant shear force. However, our simulations show that the difference $\Sigma_{yf} - \Sigma_{yv}$, and thus the discontinuity in the shear velocity, tend to zero in the infinite system size limit. Thus, our results indicate that in the large system limit, frictionless granular systems are characterized by a single static yield shear stress. We also monitor the short-time response of these systems to applied shear and show that the packing fraction of the system and shape of the velocity profile can strongly influence whether or not the shear stress at short times overshoots the long-time average value.Comment: 7 pages and 6 figure

C-N coupling between µ-aminocarbyne and nitrile ligands promoted by tolylacetylide addition to [Fe2CN(Me)(Xyl)}(CO)(CO)(NCCMe3)(Cp)2][SO3CF3]: formation of a novel bridging allene-diaminocarbene ligand

The reaction of the mu-aminocarbyne complex [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO)(NCCMe3)(CP)(2)][SO3CF3] (2) (Xyl = 2,6-Me2C6H3) with tolylacetylide, followed by treatment with HSO3CF3 affords the complex [Fe-2{mu-eta(1):eta(3)C(Tol)double bondCdouble bondC(CMe3)N(H)CN(Me)(Xyl)}(mu-CO)(CO)(Cp-2)][SO3CF3] (3) (Tol = 4-MeC6H4). The X-ray molecular structure of 3 reveals the peculiar character of the bridging ligand, which exhibits both eta(1):eta(2) allene and aminocarbene nature. The formation of 3 proceeds through several intermediate species, which have been detected by IR spectroscopy. Addition of HSO3CF3 at an early stage of the reaction between 2 and LiCdropCTol leads to the formation of the imine complex [Fe-2{mu-CN(Me)Xyl}(mu-CO)(CO){NHC(CdropCTol)CMe3}(Cp)(2)][SO3CF3] (6) indicating that the first step of the reaction consists in the acetylide addition at the coordinated NCCMe3. The molecular structure of 6 has been elucidated by an X-ray diffraction study

Husimi's Q(α)Q(\alpha) function and quantum interference in phase space

We discuss a phase space description of the photon number distribution of non classical states which is based on Husimi's $Q(\alpha)$ function and does not rely in the WKB approximation. We illustrate this approach using the examples of displaced number states and two photon coherent states and show it to provide an efficient method for computing and interpreting the photon number distribution . This result is interesting in particular for the two photon coherent states which, for high squeezing, have the probabilities of even and odd photon numbers oscillating independently.Comment: 15 pages, 12 figures, typos correcte

Hydride addition at m-vinyliminium ligand obtained from disubstituted alkynes

New μ-vinylalkylidene complexes cis-[Fe2{μ-η1:η3-Cγ(R′)Cβ(R″)CαHN(Me)(R)}(μ-CO)(CO)(Cp)2] (R = Me, R′ = R″ = Me, 3a; R = Me, R′ = R″ = Et, 3b; R = Me, R′ = R″ = Ph, 3c; R = CH2Ph, R′ = R″ = Me, 3d; R = CH2Ph, R′ = R″ = COOMe, 3e; R = CH2 Ph, R′ = SiMe3, R″ = Me, 3f) have been obtained b yreacting the corresponding vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R′)Cβ(R″)CαN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (2a–f) with NaBH4. The formation of 3a–f occurs via selective hydride addition at the iminium carbon (Cα) of the precursors 2a–f. By contrast, the vinyliminiumcis-[Fe2{μ-η1:η3-Cγ (R′) = Cβ(R″)Cα = N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (R′ = R″ = COOMe, 4a; R′ = R″ = Me, 4b; R′ = Prn, R″ = Me, 4c; Prn = CH2CH2CH3, Xyl = 2,6-Me2C6H3) undergo H− addition at the adjacent Cβ, affording the bis-alkylidene complexes cis-[Fe2{μ-η1:η2-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], (5a–c). The cis and trans isomers of [Fe2{μ-η1:η3-Cγ(Et)Cβ(Et)CαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (4d) react differently with NaBH4: the former reacts at Cα yielding cis-[Fe2{μ-η1:η3-Cγ(Et)Cβ(Et)CαHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], 6a, whereas the hydride attack occurs at Cβ of the latter, leading to the formation of the bis alkylidene trans-[Fe2{μ-η1:η2-C(Et)C(H)(Et)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (5d). The structure of 5d has been determined by an X-ray diffraction study. Other μ-vinylalkylidene complexes cis-[Fe2{μ-η1:η3-Cγ(R′)Cβ(R″)CαHN(Me)(Xyl)}(μ-CO)(CO)(Cp)2], (R′ = R″ = Ph, 6b; R′ = R″ = Me, 6c) have been prepared, and the structure of 6c has been determined by X-ray diffraction. Compound 6b results from treatment of cis-[Fe2{μ-η1:η3-Cγ(Ph)Cβ(Ph)CαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (4e) with NaBH4, whereas 6c has been obtained by reacting 4b with LiHBEt3. Both cis-4d and trans-4d react with LiHBEt3 affording cis-6a

Stereochemistry of the insertion of disubstituted alkynes into the metal aminocarbyne bond in diiron complexes

Terminal alkynes (HCdropCR') (R'=COOMe, CH2OH) insert into the metal-carbyne bond of the diiron complexes [Fe-2{mu-CN(Me)(R)} (mu-CO)(CO)(NCMe)(Cp)(2)][SO3CF3] (R=Xyl, 1a; CH2Ph, 1b; Me, 1c; Xyl=2,6-Me2C6H3), affording the corresponding mu-vinyliminium complexes [Fe-2{mu-sigma:eta(3)-C(R')=CHC=N(Me)(R)}(mu-CO)(CO)(Cp)(2)][SO3CF3] (R=Xyl, R'=COOMe, 2; R=CH2Ph, R'=COOMe, 3; R=Me, R'=COOMe, 4; R=Xyl, R'=CH2OH, 5; R=Me, R'=CH2OH, 6). The insertion is regiospecific and C-C bond formation selectively occurs between the carbyne carbon and the CH moiety of the alkyne. Disubstituted alkynes (R'CdropCR') also insert into the metal-carbyne bond leading to the formation of [Fe-2{mu-sigma:eta(3)- C(R')=C(R')C=N(Me)(R)}(mu-CO)(CO)(Cp)(2)][SO3CF3] (R'=Me, R=Xyl, 8; R'=Et, R=Xyl, 9; R'=COOMe, R=Xyl, 10; R'=COOMe, R=CH2Ph, 11; R'= COOMe, R=Me, 12). Complexes 2, 3, 5, 8, 9 and 11, in which the iminium nitrogen is unsymmetrically substituted, give rise to E and/or Z isomers. When iminium substituents are Me and Xyl, the NMR and structural investigations (X-ray structure analysis of 2 and 8) indicate that complexes obtained from terminal alkynes preferentially adopt the E configuration, whereas those derived from internal alkynes are exclusively Z. In complexes 8 and 9, trans and cis isomers have been observed, by NMR spectroscopy, and the structures of trans-8 and cis-8 have been determined by X-ray diffraction studies. Trans to cis isomerization occurs upon heating in THF at reflux temperature. In contrast to the case of HCdropCR', the insertion of 2-hexyne is not regiospecific: both [Fe-2{mu-sigma:eta(3)-C(CH2CH2CH3)=C(Me)C=N(Me)(R)} (mu-CO)(CO)(Cp)(2)][SO3CF3] (R=Xyl, 13; R=Me, 15) and [Fe-2{mu-sigma:eta(3)-C(Me)=C(CH2CH2CH3)C=N(Me)(R)}(mu-CO)(CO)(Cp)(2)][SO3CF3] (R=Xyl, 14, R=Me, 16) are obtained and these compounds are present in solution as a mixture of cis and trans isomers, with predominance of the former

Cutaneous melanoma frequencies and seasonal trend in 20 years of observation of a population characterised by excessive sun exposure

Background. Cutaneous melanoma is an aggressive form of skin cancer. It has become an increasingly common neoplasm in the most developed countries, especially among individuals of European origin. Patients and methods. Anonymous data of patients with cutaneous melanoma were collected from the diagnostic database of the University Hospital of Trieste from 1 January 1990 to 10 December 2013. Our study is based on a population which was constant over the period of observation; it was also well-defined and characterised by unrestrained sun exposure. Results. The number of cutaneous melanomas increased during the period of observation with a seasonality trend and gender related differences both for anatomical sites distribution and stage of the disease. Moreover, 6% of our cohort developed multiple melanomas. Conclusions. In a well-defined population devoted to excessive sun exposure the frequencies of skin melanomas roughly doubled from 1990 to 2013 following a seasonal trend. In that population, prevention efforts according to gender specific risk behaviour, as well as follow-up programmes both for evaluation of metastatic spreading and for early diagnosis of additional skin melanomas, are crucial due to gender specific differences and to the occurrence of multiple melanomas. \ua9 2015 Serena Bonin et al., published by De Gruyter Open