Dynamical Localization in Quasi-Periodic Driven Systems

We investigate how the time dependence of the Hamiltonian determines the occurrence of Dynamical Localization (DL) in driven quantum systems with two incommensurate frequencies. If both frequencies are associated to impulsive terms, DL is permanently destroyed. In this case, we show that the evolution is similar to a decoherent case. On the other hand, if both frequencies are associated to smooth driving functions, DL persists although on a time scale longer than in the periodic case. When the driving function consists of a series of pulses of duration $\sigma$, we show that the localization time increases as $\sigma^{-2}$ as the impulsive limit, $\sigma\to 0$, is approached. In the intermediate case, in which only one of the frequencies is associated to an impulsive term in the Hamiltonian, a transition from a localized to a delocalized dynamics takes place at a certain critical value of the strength parameter. We provide an estimate for this critical value, based on analytical considerations. We show how, in all cases, the frequency spectrum of the dynamical response can be used to understand the global features of the motion. All results are numerically checked.Comment: 7 pages, 5 figures included. In this version is that Subsection III.B and Appendix A on the quasiperiodic Fermi Accelerator has been replaced by a reference to published wor

Quantum walk as a generalized measuring device

We show that a one-dimensional discrete time quantum walk can be used to implement a generalized measurement in terms of positive operator value measure (POVM) on a single qubit. More precisely, we show that for a single qubit any set of rank 1 and rank 2 POVM elements can be generated by a properly engineered quantum walk. In such a scenario the measurement of particle at position x=i corresponds to a measurement of a POVM element E_i on a qubit. We explicitly construct quantum walks implementing unambiguous state discrimination and SIC-POVM.Comment: 6 pages, 1 figur

Los trabajadores y sus organizaciones durante los gobiernos kirchneristas

La larga década kirchnerista significó en Argentina el retorno de antiguas instituciones del mundo del trabajo, como las convenciones colectivas, de la mano del crecimiento del empleo durante buena parte del periodo 2003-2015. No obstante, el trabajo no registrado y la división entre el movimiento obrero organizado y el «otro movimiento obrero» marcaron líneas de fractura dentro del mundo de los trabajadores y pusieron en evidencia los límites de las transformaciones recientes.Fil: Abal Medina, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de General Sarmiento; Argentina. Universidad Nacional de San Martín; Argentin

Conditional Quantum Walk and Iterated Quantum Games

Iterated bipartite quantum games are implemented in terms of the discrete-time quantum walk on the line. Our proposal allows for conditional strategies, as two rational agents make a choice from a restricted set of two-qubit unitary operations. Several frequently used classical strategies give rise to families of corresponding quantum strategies. A quantum version of the Prisoner's Dilemma in which both players use mixed strategies is presented as a specific example. Since there are now quantum walk physical implementations at a proof-of principle stage, this connection may represent a step towards the experimental realization of quantum games.Comment: Revtex 4, 6 pages, 3 figures. Expanded version with one more figure and updated references. Abstract was rewritte

Spatial search in a honeycomb network

The spatial search problem consists in minimizing the number of steps required to find a given site in a network, under the restriction that only oracle queries or translations to neighboring sites are allowed. In this paper, a quantum algorithm for the spatial search problem on a honeycomb lattice with $N$ sites and torus-like boundary conditions. The search algorithm is based on a modified quantum walk on a hexagonal lattice and the general framework proposed by Ambainis, Kempe and Rivosh is used to show that the time complexity of this quantum search algorithm is $O(\sqrt{N \log N})$.Comment: 10 pages, 2 figures; Minor typos corrected, one Reference added. accepted in Math. Structures in Computer Science, special volume on Quantum Computin

Extended Advancing Front Technique for the Initial Triangular Mesh Construction on a Single Coil for Radiative Heat Transfer

Radiative heat distribution inside an ethylene cracker furnace is often modeled using the finite volume and finite element methods. In both cases, meshes in the form of rectangles and triangles are needed to form the approximating points in the domain. In this paper, a new method called extended advancing Front technique (XAFT) is proposed for meshing the domain inside the cracker furnace, integrated with the deployment of sensors on the wall to obtain the required boundary values. XAFT is the extended version of standard advancing Front technique (SAFT) where the two normal cases in SAFT are extended with six cases of study for the element creation procedure in order to generate the initial mesh. The focus of this method is to construct triangular meshes with the requirements of having the location of sensors deployed along the wall as boundary nodes and to generate nodes at certain boundaries with linearly different lengths. It is also our objective to construct the triangular element iteratively without having to re-order the Front or delete the existing element. There are two contributions from the paper. First is the introduction of six extended cases for the element creation procedure, and second is the layer concept to generate edges with linearly different lengths. XAFT provides the framework for the heat to be approximated using the discrete ordinate method, which is a variant of the finite volume method. Simulation results produced using FLUENT support the findings for effectively approximating the radiation intensity and temperature values inside the furnace

Quantum random walk on the line as a markovian process

We analyze in detail the discrete--time quantum walk on the line by separating the quantum evolution equation into Markovian and interference terms. As a result of this separation, it is possible to show analytically that the quadratic increase in the variance of the quantum walker's position with time is a direct consequence of the coherence of the quantum evolution. If the evolution is decoherent, as in the classical case, the variance is shown to increase linearly with time, as expected. Furthermore we show that this system has an evolution operator analogous to that of a resonant quantum kicked rotor. As this rotator may be described through a quantum computational algorithm, one may employ this algorithm to describe the time evolution of the quantum walker.Comment: few typos corrected, 13 pages, 2 figures, to appear in Physica

Extended Advancing Front Technique for the Initial Triangular Mesh Construction on a Single Coil for Radiative Heat Transfer

Radiative heat distribution inside an ethylene cracker furnace is often modeled using the finite volume and finite element methods. In both cases, meshes in the form of rectangles and triangles are needed to form the approximating points in the domain. In this paper, a new method called extended advancing Front technique (XAFT) is proposed for meshing the domain inside the cracker furnace, integrated with the deployment of sensors on the wall to obtain the required boundary values. XAFT is the extended version of standard advancing Front technique (SAFT) where the two normal cases in SAFT are extended with six cases of study for the element creation procedure in order to generate the initial mesh. The focus of this method is to construct triangular meshes with the requirements of having the location of sensors deployed along the wall as boundary nodes and to generate nodes at certain boundaries with linearly different lengths. It is also our objective to construct the triangular element iteratively without having to re-order the Front or delete the existing element. There are two contributions from the paper. First is the introduction of six extended cases for the element creation procedure, and second is the layer concept to generate edges with linearly different lengths. XAFT provides the framework for the heat to be approximated using the discrete ordinate method, which is a variant of the finite volume method. Simulation results produced using FLUENT support the findings for effectively approximating the radiation intensity and temperature values inside the furnace