26 research outputs found
Measuring multipartite entanglement via dynamic susceptibilities
Entanglement plays a central role in our understanding of quantum many body
physics, and is fundamental in characterising quantum phases and quantum phase
transitions. Developing protocols to detect and quantify entanglement of
many-particle quantum states is thus a key challenge for present experiments.
Here, we show that the quantum Fisher information, representing a witness for
genuinely multipartite entanglement, becomes measurable for thermal ensembles
via the dynamic susceptibility, i.e., with resources readily available in
present cold atomic gas and condensed-matter experiments. This moreover
establishes a fundamental connection between multipartite entanglement and
many-body correlations contained in response functions, with profound
implications close to quantum phase transitions. There, the quantum Fisher
information becomes universal, allowing us to identify strongly entangled phase
transitions with a divergent multipartiteness of entanglement. We illustrate
our framework using paradigmatic quantum Ising models, and point out potential
signatures in optical-lattice experiments.Comment: 5+5 pages, 3+2 figure
Redetermination of the cation distribution of spinel (MgAl2O4) by means of neutron diffraction
The cation distribution of synthetic spinel powder of grain size †50 ÎŒ was redetermined by means of neutron diffraction experiments. The oxygen parameter found by Bacon (1952) has been confirmed, but, in contradiction to Bacon, the degree of inversion amounts to about 10 to 15 %, and depends upon the thermal history of the sample.La distribution des cations dans une poudre de spinelle synthĂ©tique d'une dimension de grains infĂ©rieure Ă 50 ÎŒ a Ă©tĂ© dĂ©terminĂ©e Ă nouveau au moyen d'expĂ©riences de diffraction neutronique. Tandis que le paramĂštre d'oxygĂšne trouvĂ© par Bacon (1952) a Ă©tĂ© confirmĂ©, le degrĂ© d'inversion, par contre, est de 10 Ă 15 % et dĂ©pend de l'histoire thermique de l'Ă©chantillon
Light-induced dynamics of chlorophyll systems studied by neutron spectroscopy
Energy spectra of three chlorophyll-protein systems and of chlorophyll-a in solution were measured using the inelastic neutron scattering technique. The intensities of the observed energy spectra changed significantly when the sample was irradiated by light. This effect is interpreted in terms of electronic-vibrational relaxation mechanisms giving rise to radiationless transitions which enhance the population of the vibrational modes of all the constituents forming the sample either directly or by dissipation