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Berlin Brandenburg


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  • 1
    Description: Using a series expansion based on the flow-equation method we study the ground state energy and the elementary triplet excitations of a generalized model of crossed spin-1/2 chains starting from the limit of decoupled quadrumers. The triplet dispersion is shown to be very sensitive to the inter-quadrumer frustration, exhibiting a line of almost complete localization as well as lines of quantum phase transitions limiting the stability of the valence-bond solid phase. In the vicinity of the checkerboard-point a finite window of exchange couplings is found with a non-zero spin-gap, consistent with known results from exact diagonalization. The ground state energy is lower than that of the bare quadrumer case for all exchange couplings investigated. In the limiting situation of the fully frustrated checkerboard magnet our results agree with earlier series expansion studies. Comment: 8 pages, 7 figures
    Keywords: Condensed Matter - Strongly Correlated Electrons
    Source: Cornell University
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  • 2
    Language: English
    In: Microgravity Science and Technology, 2017, Vol.29(1), pp.37-48
    Description: We present the technical realization of a compact system for performing experiments with cold 87 Rb and 39 K atoms in microgravity in the future. The whole system fits into a capsule to be used in the drop tower Bremen. One of the advantages of a microgravity environment is long time evolution of atomic clouds which yields higher sensitivities in atom interferometer measurements. We give a full description of the system containing an experimental chamber with ultra-high vacuum conditions, miniaturized laser systems, a high-power thulium-doped fiber laser, the electronics and the power management. In a two-stage magneto-optical trap atoms should be cooled to the low μ K regime. The thulium-doped fiber laser will create an optical dipole trap which will allow further cooling to sub- μ K temperatures. The presented system fulfills the demanding requirements on size and power management for cold atom experiments on a microgravity platform, especially with respect to the use of an optical dipole trap. A first test in microgravity, including the creation of a cold Rb ensemble, shows the functionality of the system.
    Keywords: Atom interferometry ; Microgravity ; Equivalence principle ; Fundamental physics
    ISSN: 0938-0108
    E-ISSN: 1875-0494
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