9,169 research outputs found
Band structure renormalization and weak pseudogap behavior in Na_{0.33}CoO_2: Fluctuation exchange study based on a single band model
Based on a single band Hubbard model and the fluctuation exchange
approximation, the effective mass and the energy band renormalization in
NaCoO is elaborated. The renormalization is observed to exhibit
certain kind of anisotropy, which agrees qualitatively with the angle-resolved
photoemission spectroscopy (ARPES) measurements. Moreover, the spectral
function and density of states (DOS) in the normal state are calculated, with a
weak pseudogap behavior being seen, which is explained as a result of the
strong Coulomb correlations. Our results suggest that the large Fermi surface
(FS) associated with the band plays likely a central role in the
charge dynamics.Comment: 5 pages, 5 figure
Orbital-transverse density-wave instabilities in iron-based superconductors
Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFeAs (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional -like Fermi surface around (0,0) being only in 1111
parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl
Exotic Haldane Superfluid Phase of Soft-Core Bosons in Optical Lattices
We propose to realize an exotic Haldane superfluid (HSF) phase in an extended
Bose-Hubbard model on the two-leg ladder (i.e., a two-species mixture of
interacting bosons). The proposal is confirmed by means of large-scale quantum
Monte Carlo simulations, with a significant part of the ground-state phase
diagram being revealed. Most remarkably, the newly discovered HSF phase
features both superfluidity and the non-local topological Haldane order. The
effects induced by varying the number of legs are furthermore explored. Our
results shed light on how topological superfluid emerges in bosonic systems.Comment: 5 pages, 6 figures; accepted for publication in Physical Review B
(April 29, 2016
Universal holonomic quantum gates in decoherence-free subspace on superconducting circuits
To implement a set of universal quantum logic gates based on non-Abelian
geometric phases, it is a conventional wisdom that quantum systems beyond two
levels are required, which is extremely difficult to fulfil for superconducting
qubits, appearing to be a main reason why only single qubit gates was
implemented in a recent experiment [A. A. Abdumalikov Jr \emph{et al}., Nature
496, 482 (2013)]. Here we propose to realize non-adiabatic holonomic quantum
computation in decoherence-free subspace on circuit QED, where one can use only
the two levels in transmon qubits, a usual interaction, and a minimal resource
for the decoherence-free subspace encoding. In particular, our scheme not only
overcomes the difficulties encountered in previous studies, but also can still
achieve considerably large effective coupling strength, such that high fidelity
quantum gates can be achieved. Therefore, the present scheme makes it very
promising way to realize robust holonomic quantum computation with
superconducting circuits.Comment: V4: published version; V1: submitted on April
Algorithms on Minimizing the Maximum Sensor Movement for Barrier Coverage of a Linear Domain
In this paper, we study the problem of moving sensors on a line to form a
barrier coverage of a specified segment of the line such that the maximum
moving distance of the sensors is minimized. Previously, it was an open
question whether this problem on sensors with arbitrary sensing ranges is
solvable in polynomial time. We settle this open question positively by giving
an time algorithm. For the special case when all sensors have
the same-size sensing range, the previously best solution takes time.
We present an time algorithm for this case; further, if all
sensors are initially located on the coverage segment, our algorithm takes
time. Also, we extend our techniques to the cycle version of the problem
where the barrier coverage is for a simple cycle and the sensors are allowed to
move only along the cycle. For sensors with the same-size sensing range, we
solve the cycle version in time, improving the previously best
time solution.Comment: This version corrected an error in the proof of Lemma 2 in the
previous version and the version published in DCG 2013. Lemma 2 is for
proving the correctness of an algorithm (see the footnote of Page 9 for why
the previous proof is incorrect). Everything else of the paper does not
change. All algorithms in the paper are exactly the same as before and their
time complexities do not change eithe
Robust signatures of quantum radiation reaction in focused ultrashort laser pulses
Radiation reaction effects in the interaction of an electron bunch with a
superstrong focused ultrashort laser pulse are investigated in the quantum
radiation dominated regime. The angle-resolved Compton scattering spectra are
calculated in laser pulses of variable duration using a semi-classical
description for the radiation dominated dynamics and a full quantum treatment
for the emitted radiation. In dependence of the laser pulse duration we find
signatures of quantum radiation reaction in the radiation spectra, which are
characteristic for the focused laser beam and visible in the qualitative
behaviour of both the angular spread and the spectral bandwidth of the
radiation spectra. The signatures are robust with respect to the variation of
the electron and laser beam parameters in a large range. They fully differ
qualitatively from those in the classical radiation reaction regime and are
measurable with presently available laser technology
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