2,135 research outputs found
Optimized generation of spatial qudits by using a pure phase spatial light modulator
We present a method for preparing arbitrary pure states of spatial qudits,
namely, D-dimensional (D > 2) quantum systems carrying information in the
transverse momentum and position of single photons. For this purpose, a set of
D slits with complex transmission are displayed on a spatial light modulator
(SLM). In a recent work we have shown a method that requires a single
phase-only SLM to control independently the complex coefficients which define
the quantum state of dimension D. The amplitude information was codified by
introducing phase gratings inside each slit and the phase value of the complex
transmission was added to the phase gratings. After a spatial filtering process
we obtained in the image plane the desired qudit state. Although this method
has proven to be a good alternative to compact the previously reported
architectures, it presents some features that could be improved. In this paper
we present an alternative scheme to codify the required phase values that
minimizes the effects of temporal phase fluctuations associated to the SLM
where the codification is carried on. In this scheme the amplitudes are set by
appropriate phase gratings addressed at the SLM while the relative phases are
obtained by a lateral displacement of these phase gratings. We show that this
method improves the quality of the prepared state and provides very high
fidelities of preparation for any state. An additional advantage of this scheme
is that a complete 2\pi modulation is obtained by shifting the grating by one
period, and hence the encoding is not limited by the phase modulation range
achieved by the SLM. Numerical simulations, that take into account the phase
fluctuations, show high fidelities for thousands of qubit states covering the
whole Bloch sphere surface. Similar analysis are performed for qudits with D =
3 and D = 7.Comment: 12 pages, 7 figure
Improved Quantum Hard-Sphere Ground-State Equations of State
The London ground-state energy formula as a function of number density for a
system of identical boson hard spheres, corrected for the reduced mass of a
pair of particles in a sphere-of-influence picture, and generalized to fermion
hard-sphere systems with two and four intrinsic degrees of freedom, has a
double-pole at the ultimate \textit{regular} (or periodic, e.g.,
face-centered-cubic) close-packing density usually associated with a
crystalline branch. Improved fluid branches are contructed based upon exact,
field-theoretic perturbation-theory low-density expansions for many-boson and
many-fermion systems, appropriately extrapolated to intermediate densities, but
whose ultimate density is irregular or \textit{random} closest close-packing as
suggested in studies of a classical system of hard spheres. Results show
substantially improved agreement with the best available Green-function Monte
Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder,
variational Fermi hypernetted chain, and so-called L-expansion data for
two-component fermions.Comment: 15 pages and 7 figure
Experimental validation of usual numerical models of cracked beams for damage detection approaches
Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.The performances of damage detection approaches are often tested by using numerical solutions of undamaged and damaged structures. However, the numerical results used for a preliminary analysis are useful as far as they can provide a good approach to real experimental results. This paper presents a collection of numerical results obtained from three different finite element models that are extensively used in the literature for the analysis of damage detection approaches, and compare them with experimental results. The paper considers beam, plate and solid models. Natural frequencies and mode shapes of the beams are analyzed. The results show that the results obtained with 1D models are not likely to be well related to a specific experimental test, whereas 2D and 3D models provide good results if the damage is a notch, but, the do not if it is a fatigue crack
Harmonically Trapped Quantum Gases
We solve the problem of a Bose or Fermi gas in -dimensions trapped by mutually perpendicular harmonic oscillator potentials. From the
grand potential we derive their thermodynamic functions (internal energy,
specific heat, etc.) as well as a generalized density of states. The Bose gas
exhibits Bose-Einstein condensation at a nonzero critical temperature
if and only if , and a jump in the specific heat at if and
only if . Specific heats for both gas types precisely coincide as
functions of temperature when . The trapped system behaves like an
ideal free quantum gas in dimensions. For we recover
all known thermodynamic properties of ideal quantum gases in dimensions,
while in 3D for 1, 2 and 3 one simulates behavior reminiscent of
quantum {\it wells, wires}and{\it dots}, respectively.Comment: 14 pages including 3 figures and 3 table
DC-Voltage-Ratio Control Strategy for Multilevel Cascaded Converters Fed With a Single DC Source
Recently, a multilevel cascaded converter fed with a single DC source has been presented. An analysis of the steady-state working limits of this type of converter is presented in this paper. Limits of the maximum output voltage and the minimum and maximum loading conditions for stable operation of the converter are addressed. In this paper, a way to achieve any DC voltage ratio (inside the stable operation area of the converter) between the H-bridges of the single-DC-source cascaded H-bridge converter is presented. The proposed DC-voltage-ratio control is based on a time-domain modulation strategy that avoids the use of inappropriate states to achieve the DC-voltage-ratio control. The proposed technique is a feedforward-modulation technique which takes into account the actual DC voltage of each H-bridge of the converter, leading to output waveforms with low distortion. In this way, the dc voltage of the floating H-bridge can be controlled while the output voltage has low distortion independently of the desired DC voltage ratio. Experimental results from a two-cell cascaded converter are presented in order to validate the proposed DC-voltage-ratio control strategy and the introduced concepts.Ministerio de Ciencia y TecnologĂa TEC2006-03863Junta de AndalucĂa EXC/2005/TIC-117
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