2,321 research outputs found
Keeping a Quantum Bit Alive by Optimized -Pulse Sequences
A general strategy to maintain the coherence of a quantum bit is proposed.
The analytical result is derived rigorously including all memory and
back-action effects. It is based on an optimized -pulse sequence for
dynamic decoupling extending the Carr-Purcell-Meiboom-Gill (CPMG) cycle. The
optimized sequence is very efficient, in particular for strong couplings to the
environment.Comment: 4 pages, 2 figures; revised version with additional references for
better context, more stringent discussio
Poisson-Lie T-dual sigma models on supermanifolds
We investigate Poisson-Lie symmetry for T-dual sigma models on supermanifolds
in general and on Lie supergroups in particular. We show that the integrability
condition on this super Poisson-Lie symmetry is equivalent to the super Jacobi
identities of the Lie super-bialgebras. As examples we consider models related
to four dimensional Lie super-bialgebras and
. Then generally it is shown that for Abelian case (g, I)
the super Poisson-Lie T-duality transforms the role of fermionic (bosonic)
fields in the model to bosonic (fermionic) fields on the dual model and vice
versa.Comment: 13 pages, Revised and accepted for publication in JHE
A simplified approach to the magnetic blue shift of Mott gaps
The antiferromagnetic ordering in Mott insulators upon lowering the
temperature is accompanied by a transfer of the single-particle spectral weight
to lower energies and a shift of the Mott gap to higher energies (magnetic blue
shift, MBS). The MBS is governed by the double exchange and the exchange
mechanisms. Both mechanisms enhance the MBS upon increasing the number of
orbitals. We provide an expansion for the MBS in terms of hopping and exchange
coupling of a prototype Hubbard-Kondo-Heisenberg model and discuss how the
results can be generalized for application to realistic Mott or charge-transfer
insulator materials. This allows estimating the MBS of the charge gap in real
materials in an extremely simple way avoiding extensive theoretical
calculations. The approach is exemplarily applied to -MnTe, NiO, and
BiFeO and an MBS of about meV, meV, and meV is found,
respectively. The values are compared with the previous theoretical
calculations and the available experimental data. Our ready-to-use formula for
the MBS simplifies the future studies searching for materials with a strong
coupling between the antiferromagnetic ordering and the charge excitations,
which is paramount to realize a coupled spin-charge coherent dynamics at a
femtosecond time scale.Comment: 16 pages, 13 figure
Kinks in the electronic dispersion of the Hubbard model away from half filling
We study kinks in the electronic dispersion of a generic strongly correlated
system by dynamic mean-field theory (DMFT). The focus is on doped systems away
from particle-hole symmetry where valence fluctuations matter potentially.
Three different algorithms are compared to asses their strengths and
weaknesses, as well as to clearly distinguish physical features from
algorithmic artifacts. Our findings extend a view previously established for
half-filled systems where kinks reflect the coupling of the fermionic
quasiparticles to emergent collective modes, which are identified here as spin
fluctuations. Kinks are observed when strong spin fluctuations are present and,
additionally, a separation of energy scales for spin and charge excitations
exists. Both criteria are met by strongly correlated systems close to a
Mott-insulator transition. The energies of the kinks and their doping
dependence fit well to the kinks in the cuprates, which is surprising in view
of the spatial correlations neglected by DMFT.Comment: 13 pages, 15 figure
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