3,309 research outputs found
Nonlinear behavior of geometric phases induced by photon pairs
In this study, we observe the nonlinear behavior of the two-photon geometric
phase for polarization states using time-correlated photons pairs. This phase
manifests as a shift of two-photon interference fringes. Under certain
arrangements, the geometric phase can vary nonlinearly and become very
sensitive to a change in the polarization state. Moreover, it is known that the
geometric phase for identically polarized photons is times larger than
that for one photon. Thus, the geometric phase for two photons can become two
times more sensitive to a state change. This high sensitivity to a change in
the polarization can be exploited for precision measurement of small
polarization variation. We evaluate the signal-to-noise ratio of the
measurement scheme using the nonlinear behavior of the geometric phase under
technical noise and highlight the practical advantages of this scheme.Comment: 10 pages, 10 figure
Dynamic fluctuations in the superconductivity of NbN films from microwave conductivity measurements
We have measured the frequency and temperature dependences of complex ac
conductivity, \sigma(\omega)=\sigma_1(\omega)-i\sigma_2(\omega), of NbN films
in zero magnetic field between 0.1 to 10 GHz using a microwave broadband
technique. In the vicinity of superconducting critical temperature, Tc, both
\sigma_1(\omega) and \sigma_2(\omega) showed a rapid increase in the low
frequency limit owing to the fluctuation effect of superconductivity. For the
films thinner than 300 nm, frequency and temperature dependences of fluctuation
conductivity, \sigma(\omega,T), were successfully scaled onto one scaling
function, which was consistent with the Aslamazov and Larkin model for two
dimensional (2D) cases. For thicker films, \sigma(\omega,T) data could not be
scaled, but indicated that the dimensional crossover from three dimensions (3D)
to 2D occurred as the temperature approached Tc from above. This provides a
good reference of ac fluctuation conductivity for more exotic superconductors
of current interest.Comment: 8 pages, 7 Figures, 1 Table, Accepted for publication in PR
Scaling theory of transport in complex networks
Transport is an important function in many network systems and understanding
its behavior on biological, social, and technological networks is crucial for a
wide range of applications. However, it is a property that is not
well-understood in these systems and this is probably due to the lack of a
general theoretical framework. Here, based on the finding that renormalization
can be applied to bio-networks, we develop a scaling theory of transport in
self-similar networks. We demonstrate the networks invariance under length
scale renormalization and we show that the problem of transport can be
characterized in terms of a set of critical exponents. The scaling theory
allows us to determine the influence of the modular structure on transport. We
also generalize our theory by presenting and verifying scaling arguments for
the dependence of transport on microscopic features, such as the degree of the
nodes and the distance between them. Using transport concepts such as diffusion
and resistance we exploit this invariance and we are able to explain, based on
the topology of the network, recent experimental results on the broad flow
distribution in metabolic networks.Comment: 8 pages, 6 figure
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Modeling of Viscous Shock Tube Using ES-BGK Model Kinetic Equations
The viscous effects on unsteady shock wave propagation are investigated by numerical solution of the Boltzmann model kinetic equations. The kinetic equations are solved for two unsteady non-equilibrium flow problems, namely, the one-dimensional Riemann problem and a two-dimensional viscous shock-tube. The numerical method comprises the discrete velocity method in the velocity space and the finite volume discretization in physical space using various flux schemes. The discrete version of H-theorem is applied for analysis of accuracy of the numerical solution as well as of the onset of non-equilibrium. Simulations show that the maximum entropy generation rate in viscous shock tube occurs in the boundary layer / shock wave interaction region. The entropy generation rate is used to determine the time-variation of the speed of propagation of shock, contact discontinuity and rarefaction waves
Bloch sphere representation of three-vertex geometric phases
The properties of the geometric phases between three quantum states are
investigated in a high-dimensional Hilbert space using the Majorana
representation of symmetric quantum states. We found that the geometric phases
between the three quantum states in an N-state quantum system can be
represented by N-1 spherical triangles on the Bloch sphere. The parameter
dependence of the geometric phase was analyzed based on this picture. We found
that the geometric phase exhibits rich nonlinear behavior in a high-dimensional
Hilbert space.Comment: 5 pages, 4 figure
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