93 research outputs found
Multipartite entanglement theory with entanglement-nonincreasing operations
A key problem in quantum information science is to determine optimal
protocols for the interconversion of entangled states shared between remote
parties. While for two parties a large number of results in this direction is
available, the multipartite setting still remains a major challenge. In this
Letter, this problem is addressed by extending the resource theory of
entanglement for multipartite systems beyond the standard framework of local
operations and classical communication. Specifically, we consider
transformations capable of introducing a small, controllable increase of
entanglement of a state, with the requirement that the increase can be made
arbitrarily small. We demonstrate that in this adjusted framework, the
transformation rates between multipartite states are fundamentally dictated by
the bipartite entanglement entropies of the respective quantum states.
Remarkably, this approach allows the reduction of tripartite entanglement to
its bipartite analog, indicating that every pure tripartite state can be
reversibly synthesized from a suitable number of singlets distributed between
pairs of parties.Comment: 5+6 pages, 2 figure
Electronic correlations and competing orders in multiorbital dimers: a cluster DMFT study
We investigate the violation of the first Hund's rule in 4 and 5
transition metal oxides that form solids of dimers. Bonding states within these
dimers reduce the magnetization of such materials. We parametrize the dimer
formation with realistic hopping parameters and find not only regimes, where
the system behaves as a Fermi liquid or as a Peierls insulator, but also
strongly correlated regions due to Hund's coupling and its competition with the
dimer formation. The electronic structure is investigated using the cluster
dynamical mean-field theory for a dimer in the two-plane Bethe lattice with two
orbitals per site and -filling, that is three electrons per dimer. It
reveals dimer-antiferromagnetic order of a high-spin (double exchange) state
and a low-spin (molecular orbital) state. At the crossover region we observe
the suppression of long-range magnetic order, fluctuation enhancement and
renormalization of electron masses. At certain interaction strengths the system
becomes an incoherent antiferromagnetic metal with well defined local moments.Comment: 11 pages, 10 figure
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