515 research outputs found
Systematic Analysis of Frustration Effects in Anisotropic Checkerboard Lattice Hubbard Model
We study the ground state properties of the geometrically frustrated Hubbard
model on the anisotropic checkerboard lattice with nearest-neighbor hopping
and next nearest-neighbor hopping . By using the path-integral
renormalization group method, we study the phase diagram in the parameter space
of the Hubbard interaction and the frustration-control parameter .
Close examinations of the effective hopping, the double occupancy, the momentum
distribution and the spin/charge correlation functions allow us to determine
the phase diagram at zero temperature, where the plaquette-singlet insulator
emerges besides the antiferromagnetic insulator and the paramagnetic metal.
Spin-liquid insulating states without any kind of symmetry breaking cannot be
found in our frustrated model.Comment: 7pages, 5figure
Influence of pure-dephasing by phonons on exciton-photon interfaces: Quantum microscopic theory
We have developed a full quantum microscopic theory to analyze the time
evolution of transversal and longitudinal components of an exciton-single
photon system coupled to bulk acoustic phonons. These components are subjected
to two decay processes. One is radiative relaxation and the other is
pure-dephasing due to exciton-phonon interaction. The former results in a decay
with an exponent linear to time, while the latter causes a faster initial decay
than the radiative decay. We analyzed the dependence of the components on the
duration of the input one-photon pulse, temperature, and radiative relaxation
rates. Such a quantitative analysis is important for the developments of
atom-photon interfaces which enable coherent transfer of quantum information
between photons and atomic systems. We found that, for a GaAs spherical quantum
dot in which the exciton interacts with bulk phonons, the maximal probability
of the excited state can be increased up to 75 %. This probability can be
considered as the efficiency for quantum information transfer from photon to
exciton.Comment: 9pages, 5figure
Measured Quantum Fourier Transform of 1024 Qubits on Fiber Optics
Quantum Fourier transform (QFT) is a key function to realize quantum
computers. A QFT followed by measurement was demonstrated on a simple circuit
based on fiber-optics. The QFT was shown to be robust against imperfections in
the rotation gate. Error probability was estimated to be 0.01 per qubit, which
corresponded to error-free operation on 100 qubits. The error probability can
be further reduced by taking the majority of the accumulated results. The
reduction of error probability resulted in a successful QFT demonstration on
1024 qubits.Comment: 15 pages, 6 figures, submitted to EQIS 2003 Special issue, Int. J.
Quantum Informatio
Ferromagnetism of cold fermions loaded into a decorated square lattice
We investigate two-component ultracold fermions loaded into a decorated
square lattice, which are described by the Hubbard model with repulsive
interactions and nearest neighbor hoppings. By combining the real-space
dynamical mean-field theory with the numerical renormalization group method, we
discuss how a ferromagnetically ordered ground state in the weak coupling
regime, which originates from the existence of a dispersionless band, is
adiabatically connected to a Heisenberg ferrimagnetic state in the strong
coupling limit. The effects of level splitting and hopping imbalance are also
addressed.Comment: 8 pages, 7 figure
Mott insulating state in a quarter-filled two-orbital Hubbard chain with different bandwidths
We investigate the ground-state properties of the one-dimensional two-band
Hubbard model with different bandwidths. The density-matrix renormalization
group method is applied to calculate the averaged electron occupancies as a
function of the chemical potential . Both at quarter and half fillings,
"charge plateaux" appear in the - plot, where diverges and
the Mott insulating states are realized. To see how the orbital polarization in
the one-quarter charge plateau develops, we apply the second-order perturbation
theory from the strong-coupling limit at quarter filling. The resultant
Kugel-Khomskii spin-orbital model includes a field coupled to
orbital pseudo-spins. This field originates from the discrepancy between the
two bandwidths and leads to a finite orbital pseudo-spin magnetization.Comment: 4 pages, 2 figures, Proceedings of LT2
Finite-temperature Mott transitions in multi-orbital Hubbard model
We investigate the Mott transitions in the multi-orbital Hubbard model at
half-filling by means of the self-energy functional approach. The phase
diagrams are obtained at finite temperatures for the Hubbard model with up to
four-fold degenerate bands. We discuss how the first-order Mott transition
points and as well as the critical temperature depend
on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations
play a key role to control the Mott transitions in the multi-orbital Hubbard
model.Comment: 8 pages, 7 figure
Spin, charge and orbital fluctuations in a multi-orbital Mott insulator
The two-orbital degenerate Hubbard model with distinct hopping integrals is
studied by combining dynamical mean-field theory with quantum Monte Carlo
simulations. The role of orbital fluctuations for the nature of the Mott
transition is elucidated by examining the temperature dependence of spin,
charge and orbital susceptibilities as well as the one-particle spectral
function. We also consider the effect of the hybridization between the two
orbitals, which is important particularly close to the Mott transition points.
The introduction of the hybridization induces orbital fluctuations, resulting
in the formation of a Kondo-like heavy-fermion behavior, similarly to
electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure
Statistical analysis on testing of an entangled state based on Poisson distribution framework
A hypothesis testing scheme for entanglement has been formulated based on the
Poisson distribution framework instead of the POVM framework. Three designs
were proposed to test the entangled states in this framework. The designs were
evaluated in terms of the asymptotic variance. It has been shown that the
optimal time allocation between the coincidence and anti-coincidence
measurement bases improves the conventional testing method. The test can be
further improved by optimizing the time allocation between the anti-coincidence
bases.Comment: This paper is an extended version of the theoretical part of v1 of
quant-ph/0603254.quant-ph/0603254 is revised so that it is more familiar to
experimentalist
Existence of the Wigner function with correct marginal distributions along tilted lines on a lattice
In order to determine the Wigner function uniquely, we introduce a new
condition which ensures that the Wigner function has correct marginal
distributions along tilted lines. For a system in dimensional Hilbert
space, whose "phase space" is a lattice with sites, we get different
results depending on whether is odd or even. Under the new condition, the
Wigner function is determined if is an odd number, but it does not exist if
is even.Comment: 18 page
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