13 research outputs found
Evaluation of heat extraction through sapphire fibers for the GW observatory KAGRA
Currently, the Japanese gravitational wave laser interferometer KAGRA is
under construction in the Kamioka mine. As one main feature, it will employ
sapphire mirrors operated at a temperature of 20K to reduce the impact from
thermal noise. To reduce seismic noise, the mirrors will also be suspended from
multi-stage pendulums. Thus the heat load deposited in the mirrors by
absorption of the circulating laser light as well as heat load from thermal
radiation will need to be extracted through the last suspension stage. This
stage will consist of four thin sapphire fibers with larger heads necessary to
connect the fibers to both the mirror and the upper stage. In this paper, we
discuss heat conductivity measurements on different fiber candidates. While all
fibers had a diameter of 1.6mm, different surface treatments and approaches to
attach the heads were analyzed. Our measurements show that fibers fulfilling
the basic KAGRA heat conductivity requirement of 5000W/m/K at 20K
are technologically feasible.Comment: 11 pages, 4 figure
Multipartite entanglement in the 1-D spin- Heisenberg Antiferromagnet
Multipartite entanglement refers to the simultaneous entanglement between
multiple subsystems of a many-body quantum system. While multipartite
entanglement can be difficult to quantify analytically, it is known that it can
be witnessed through the Quantum Fisher information (QFI), a quantity that can
also be related to dynamical Kubo response functions. In this work, we first
show that the finite temperature QFI can generally be expressed in terms of a
static structure factor of the system, plus a correction that vanishes as
. We argue that this implies that the static structure factor
witnesses multipartite entanglement near quantum critical points at
temperatures below a characteristic energy scale that is determined by
universal properties, up to a non-universal amplitude. Therefore, in systems
with a known static structure factor, we can deduce finite temperature scaling
of multipartite entanglement and low temperature entanglement depth without
knowledge of the full dynamical response function of the system. This is
particularly useful to study 1D quantum critical systems in which sub-power-law
divergences can dominate entanglement growth, where the conventional scaling
theory of the QFI breaks down. The 1D spin- antiferromagnetic
Heisenberg model is an important example of such a system, and we show that
multipartite entanglement in the Heisenberg chain diverges non-trivially as
. We verify these predictions with calculations of the
QFI using conformal field theory and matrix product state simulations. Finally
we discuss the implications of our results for experiments to probe
entanglement in quantum materials, comparing to neutron scattering data in
KCuF, a material well-described by the Heisenberg chain.Comment: 8 pages and 3 figures; 1 page and 1 figure of the appendix; typos
corrected; references adde
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Multipartite entanglement in the one-dimensional spin-12 Heisenberg antiferromagnet
Multipartite entanglement refers to the simultaneous entanglement between multiple subsystems of a many-body quantum system. While multipartite entanglement can be difficult to quantify analytically, it is known that it can be witnessed through the quantum Fisher information (QFI), a quantity that can also be related to dynamical Kubo response functions. In this work, we first show that the finite temperature QFI can generally be expressed in terms of a static structure factor of the system, plus a correction that vanishes as T→0. This implies that the static structure factor witnesses multipartite entanglement near quantum critical points at temperatures below a characteristic energy scale of the system. Therefore, in systems with a known static structure factor, we can deduce finite temperature scaling of multipartite entanglement and low temperature entanglement depth without knowledge of the full dynamical response function of the system. This is particularly useful to study 1D quantum critical systems in which sub-power-law divergences can dominate entanglement growth, where the conventional scaling theory of the QFI breaks down. The 1D spin-12 antiferromagnetic Heisenberg model is an important example of such a system, and we show that multipartite entanglement in the Heisenberg chain diverges nontrivially as ∼ln(1/T)3/2. We verify these predictions with calculations of the QFI using conformal field theory and matrix product state simulations. Finally we discuss the implications of our results for experiments to probe entanglement in quantum materials, comparing to neutron scattering data in KCuF3, a material well described by the Heisenberg chain
Crystal field levels and magnetic anisotropy in the kagome compounds Nd3Sb3Mg2 O14, Nd3Sb3Zn2 O14, and Pr3Sb3Mg2 O14
Physical Review B
Volume 98, Issue 13, 1 October 2018, Article number 134401© 2018 American Physical Society. We report the crystal field levels of several newly discovered rare-earth kagome compounds: Nd3Sb3Mg2O14, Nd3Sb3Zn2O14, and Pr3Sb3Mg2O14. We determine the crystal electric field (CEF) Hamiltonian by fitting to neutron scattering data using a point charge Hamiltonian as an intermediate fitting step. The fitted Hamiltonians accurately reproduce bulk susceptibility measurements, and the results indicate easy-axis ground-state doublets for Nd3Sb3Mg2O14 and Nd3Sb3Zn2O14 and a singlet ground state for Pr3Sb3Mg2O14. These results provide the groundwork for future investigations of these compounds and a template for CEF analysis of other low-symmetry materials