*Liu, B.-H., *Li, L., *Huang, Y.-F., *Li, C.-F., *Guo, G.-C., Laine, E.-M., *Breuer, H.-P., and Piilo, J. 2011: Experimental control of the transition from Markovian to non-Markovian dynamics of open quantum systems. - Nature Physics 7, 931-934.
Realistic quantum mechanical systems are always exposed to an external environment. This often induces Markovian processes in which the system loses information to its surroundings. However, many quantum systems exhibit non-Markovian behavior with a flow of information from the environment back to the system. The environment usually consists of large number of degrees of freedom which are difficult to control, but some sophisticated schemes for reservoir engineering have been developed. The control of open systems plays a decisive role, for example, in proposals for entanglement generation and dissipative quantum computation, for the design of quantum memories and in quantum metrology. Here we report an all-optical experiment which allows to drive the open system from the Markovian to the non-Markovian regime, to control the information flow between the system and the environment, and to determine the degree of non-Markovianity by measurements on the open system. (5.10.2011)
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Hietarinta, J, and *Viallet, C. 2011: Integrable lattice equations with vertex and bond variables. – Journal of Physics A 44, 385201
We present integrable lattice equations on a two-dimensional square lattice with coupled vertex and bond variables. In some of the models, the vertex dynamics is independent of the evolution of the bond variables, and one can write the equations as non-autonomous 'Yang-Baxter maps'. We also present a model in which the vertex and bond variables are fully coupled. Integrability is tested with algebraic entropy as well as multidimensional consistency. (5.10.2011)
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*Ropo, M., Kokko, K., Airiskallio, E., Punkkinen, M.P.J., *Hogmark, S., *Kollár, J., *Johansson, B., and *Vitos, L. 2011: First-principles atomistic study of Fe-rich Fe-Cr surfaces. – Journal of Physics: Condensed Matter 23, 265004.
The surface properties of Fe-rich ferromagnetic Fe-Cr alloys are investigated using a first-principles quantum-mechanical method. In dilute alloys, the surfaces are dominated by Fe, whereas the Cr-containing surfaces become favorable when bulk Cr concentration exceeds the limit of about 10 atomic percent. The abrupt change in the surface behavior is the consequence of complex competing magnetochemical interactions between the alloying atoms. Considering quantities of various features: equilibrium surface profiles, chemical potentials, segregation energies, surface energies, magnetic moments, mixing energies and pair interactions, within a wider range of bulk and surface concentrations enables to build a comprehensive picture of the physics of Fe-Cr surfaces. Using the present achievements many previously controversial results can now be merged into a consistent model of Fe-rich Fe-Cr alloys. (02.09.2011)
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Punkkinen, M.P.J., Laukkanen, P., Lang, J., Kuzmin, M., Tuominen, M., Tuominen, V., Dahl, J., *Pessa, M., *Guina, M., Kokko, K., *Sadowski, J., Johansson, B., Vayrynen, I.J., and *Vitos, L. 2011: Oxidized In-containing III-V(100) surfaces: Formation of crystalline oxide films and semiconductor-oxide interfaces. – Physical Review B 83, 195329.
Previously found oxidized III-V semiconductor surfaces have been generally structurally disordered and useless for applications. We disclose a family of well-ordered oxidized InAs, InGaAs, InP, and InSb surfaces found by experiments. The found epitaxial oxide-III-V interface is insulating and free of defects related to the harmful Fermi-level pinning, which opens up new possibilities to develop long-sought III-V metal-oxide-semiconductor transistors. Calculations reveal that the early stages in the oxidation process include only O-III bonds due to the geometry of the III-V(100)c(8x2) substrate, which is responsible for the formation of the ordered interface. The found surfaces provide a different platform to study the oxidation and properties of oxides, e.g., the origins of the photoemission shifts and electronic structures, using surface science methods. (08.08.2011)
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Hietarinta, J. 2011: Boussinesq-like multi-component lattice equations and multi-dimensional consistency. – Journal of Physics A 44, 165204.
Various classes of one-component lattice equations, defined by a multilinear relation between values at the vertices of an elementary square, have recently been classified using the requirement of multi-dimensional consistency (consistency-around-the-cube, CAC). Here we consider multi-component equations, with some equations defined on the edges of the consistency cube and others on the faces of the cube. Some examples of this type are already known, including the lattice-modified Boussinesq equation (lmBSQ). We classify the edge equations into three canonical forms and derive the consequences of their CAC-property. This restricts the form of the face equation sufficiently so that its CAC-property can be analyzed. As a result we obtain a number of integrable multi-component lattice equations, some generalizing lmBSQ. (19.04.2011)
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