6,826 research outputs found
Kondo and Dicke effect in quantum-dots side coupled to a quantum wire
Electron tunneling through quantum-dots side coupled to a quantum wire, in
equilibrium and nonequilibrium Kondo regime, is studied. The mean-field
finite- slave-boson formalism is used to obtain the solution of the problem.
We have found that the transmission spectrum shows a structure with two
anti-resonances localized at the renormalized energies of the quantum dots. The
DOS of the system shows that when the Kondo correlations are dominant there are
two Kondo regimes with its own Kondo temperature. The above behavior of the DOS
can be explained by quantum interference in the transmission through the two
different resonance states of the quantum dots coupled to common leads. This
result is analogous to the Dicke effect in optics. We investigate the many body
Kondo states as a function of the parameters of the system.Comment: 5 figures. To appear in Phys. Rev.
ALTERNATIVE DIRECT INTERPOLATION BOUNDARY ELEMENT METHOD APPLIED TO ADVECTIVE-DIFFUSIVE PROBLEMS WITH VARIABLE VELOCITY FIELD
The wide range of physical phenomena of industrial interest which can be properly represented by advection-diffusion transport models motivates a constant effort in the development of new numerical methods capable of dealing with strong advective effects such as compressibility ones. The recent direct interpolation technique (DIBEM) proved to be an accurate and reliable tool for the representation of problems with constant velocity field and initial tests were also performed for problems with variable velocity field, where the results are reasonably satisfactory, but not so robust, since the integral relative to the velocity divergence, in general, seems to disturb the performance of the formulation. The current article presents a new formulation of the direct interpolation technique for solving variable velocity problems with non-zero velocity divergence. The accuracy of the new proposal is measured against a known analytical solution and, also, contrasted with the classical formulation of DIBEM and dual reciprocity technique (DRBEM) for the same case. Preliminary results show that the alternative DIBEM formulation proposed promotes a consistent improvement in precision, outperforming the two techniques in cross-comparison
Simulation of static and random errors on Grover's search algorithm implemented in a Ising nuclear spin chain quantum computer with few qubits
We consider Grover's search algorithm on a model quantum computer implemented
on a chain of four or five nuclear spins with first and second neighbour Ising
interactions. Noise is introduced into the system in terms of random
fluctuations of the external fields. By averaging over many repetitions of the
algorithm, the output state becomes effectively a mixed state. We study its
overlap with the nominal output state of the algorithm, which is called
fidelity. We find either an exponential or a Gaussian decay for the fidelity as
a function of the strength of the noise, depending on the type of noise (static
or random) and whether error supression is applied (the 2pi k-method) or not.Comment: 18 pages, 8 figures, extensive revision with new figure
Radio Spectra of Giant Radio Galaxies from RATAN-600 Data
Measurements of the flux densities of the extended components of seven giant
radio galaxies obtained using the RATAN-600 radio telescope at wavelengths of
6.25 and 13 cm ar e presented. The spectra of components of these radio
galaxies are constructed using these new RA TAN-600 data together with data
from the WENSS, NVSS, and GB6 surveys. The spectral indices in the stu died
frequency range are calculated, and the need for detailed estimates of the
integrated contributi on of such objects to the background emission is
demonstrated.Comment: 7 pages, 2 figures, 5 table
Numerical simulation of a Controlled-Controlled-Not (CCN) quantum gate in a chain of three interacting nuclear spins system
We present the study of a quantum Controlled-Controlled-Not gate, implemented
in a chain of three nuclear spins weakly Ising interacting between all of them,
that is, taking into account first and second neighbor spin interactions. This
implementation is done using a single resonant -pulse on the initial state
of the system (digital and superposition). The fidelity parameter is used to
determine the behavior of the CCN quantum gate as a function of the ratio of
the second neighbor interaction coupling constant to the first neighbor
interaction coupling constant (). We found that for we can
have a well defined CCN quantum gate.Comment: 9 pages, 5 fugure
Photoactivatable organometallic pyridyl ruthenium(II) arene complexes
The synthesis and characterization of a family of piano-stool RuII arene complexes of the type [(η6-arene)Ru(N,N′)(L)][PF6]2, where arene is p-cymene (p-cym), hexamethylbenzene (hmb), or indane (ind), N,N′ is 2,2′-bipyrimidine (bpm), 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendio), or 4,7-diphenyl-1,10-phenanthroline (bathophen), and L is pyridine (Py), 4-methylpyridine (4-MePy), 4-methoxypyridine (4-MeOPy), 4,4′-bipyridine (4,4′-bpy), 4-phenylpyridine (4-PhPy), 4-benzylpyridine (4-BzPy), 1,2,4-triazole (trz), 3-acetylpyridine (3-AcPy), nicotinamide (NA), or methyl nicotinate (MN), are reported, including the X-ray crystal structures of [(η6-p-cym)Ru(bpm)(4-MePy)]2+ (2), [(η6-p-cym)Ru(bpm)(4-BzPy)]2+ (6), [(η6-p-cym)Ru(bpm)(trz)]2+ (7), [(η6-p-cym)Ru(phen)(Py)]2+ (10), and [(η6-ind)Ru(bpy)(Py)]2+ (13). These complexes can selectively photodissociate the monodentate ligand (L) when excited with UVA or white light, allowing strict control of the formation of the reactive aqua species [(η6-arene)Ru(N,N′)(OH2)]2+ that otherwise would not form in the dark. The photoproducts were characterized by UV–vis absorption and 1H NMR spectroscopy. DFT and TD-DFT calculations were employed to characterize the excited states and to obtain information on the photochemistry of the complexes. All the RuII pyridine complexes follow a relatively similar photochemical L-ligand dissociation mechanism, likely to occur from a series of 3MC triplet states with dissociative character. The photochemical process proved to be much more efficient when UVA-range irradiation was used. More strikingly, light activation was used to phototrigger binding of these potential anticancer agents with discriminating preference toward 9-ethylguanine (9-EtG) over 9-ethyladenine (9-EtA). Calf thymus (CT)-DNA binding studies showed that the irradiated complexes bind to CT-DNA, whereas the nonirradiated forms bind negligibly. Studies of CT-DNA interactions in cell-free media suggest combined weak monofunctional coordinative and intercalative binding modes. The RuII arene complexes [(η6-p-cym)Ru(bpm)(Py)]2+ (1), [(η6-p-cym)Ru(bpm)(4-MeOPy)]2+ (3), [(η6-p-cym)Ru(4,4′-bpy)]2+ (4), [(η6-hmb)Ru(bpm)(Py)]2+ (8), [(η6-ind)Ru(bpm)(Py)]2+ (9), [(η6-p-cym)Ru(phen)(Py)]2+ (10), [(η6-p-cym)Ru(bathophen)(Py)]2+ (12), [(η6-p-cym)Ru(bpm)(NA)]2+ (15), and [(η6-p-cym)Ru(bpm)(MN)]2+ (16) were cytotoxic toward A2780 human ovarian cancer cell line in the absence of photoirradiation (IC50 values in the range of 9.0–60 μM)
Correlation Effects in Side-Coupled Quantum Dots
Using Wilson's numerical renormalization group (NRG) technique we compute
zero-bias conductance and various correlation functions of a double quantum dot
(DQD) system. We present different regimes within a phase diagram of the DQD
system. By introducing a negative Hubbard U on one of the quantum dots, we
simulate the effect of electron-phonon coupling and explore the properties of
the coexisting spin and charge Kondo state. In a triple quantum dot (TQD)
system a multi-stage Kondo effect appears where localized moments on quantum
dots are screened successively at exponentially distinct Kondo temperatures.Comment: 13 pages, 10 figure
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