arXiv subjects

A. Perez

Publications and source records attributed to A. Perez.

At least 19 recordsLinked to original sources

arXiv2017

Fermion confinement via Quantum Walks in 2D+1 and 3D+1 spacetime

We analyze the properties of a two and three dimensional quantum walk that are inspired by the idea of a brane-world model put forward by Rubakov and Shaposhnikov [1]. In that model, particles are dynamically confined on the brane due to the interaction with a scalar field. We translated this model into an alternate quantum walk with a coin that depends on the external field, with a dependence which mimics a domain wall solution. As in the original model, fermions (in our case, the walker), become localized in one of the dimensions, not from the action of a random noise on the lattice (as in the case of Anderson localization), but from a regular dependence in space. On the other hand, the resulting quantum walk can move freely along the "ordinary" dimension.

quant-ph↗

arXiv2015

Current status of the Standard Model CKM fit and constraints on $ΔF=2$ New Physics

This letter summarises the status of the global fit of the CKM parameters within the Standard Model performed by the CKMfitter group. Special attention is paid to the inputs for the CKM angles $α$ and $γ$ and the status of $B_s\toμμ$ and $B_d\to μμ$ decays. We illustrate the current situation for other unitarity triangles. We also discuss the constraints on generic $ΔF=2$ New Physics. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using Rfit to handle theoretical uncertainties.

hep-ph↗

arXiv2015

Nonlinear interferometer for tailoring the frequency spectrum of bright squeezed vacuum

We propose a method for tailoring the frequency spectrum of bright squeezed vacuum by generating it in a nonlinear interferometer, consisting of two down-converting nonlinear crystals separated by a dispersive medium. Due to a faster dispersive spreading of higher-order Schmidt modes, the spectral width of the radiation at the output is reduced as the length of the dispersive medium is increased. Preliminary results show 30\% spectral narrowing.

quant-ph↗

arXiv2013

Macrodeterminism without non-invasive measurability

We propose a definition of determinism for a physical system that includes, besides the measured system, the measurement device and the surrounding environment. This enlarged system is assumed to follow a predefined trajectory starting from some (unknown) initial conditions that play the role of hidden variables for the experiment. These assumptions, which are different from realism, allow us to derive some Leggett-Garg inequalities, which are violated by Quantum Mechanics in the particular case of consecutive measurements on individual photon polarizations.

quant-ph↗

arXiv2013

Determinism and Quantum Mechanics with time Bell inequalities

We propose a definition of determinism for a physical system that includes, besides the measurement device, the surrounding environment. This enlarged system is assumed to follow a predefined trajectory starting from some (unknown) initial conditions that play the role of hidden variables for the experiment. These assumptions, which are different from realism, allow us to derive a type of time Bell inequalities, which are violated by Quantum Mechanics. In order to illustrate this violation, we discuss the particular case of measurements on a spin 1/2 particle.

quant-ph↗

arXiv2012

A study of Wigner functions for discrete-time quantum walks

We perform a systematic study of the discrete time Quantum Walk on one dimension using Wigner functions, which are generalized to include the chirality (or coin) degree of freedom. In particular, we analyze the evolution of the negative volume in phase space, as a function of time, for different initial states. This negativity can be used to quantify the degree of departure of the system from a classical state. We also relate this quantity to the entanglement between the coin and walker subspaces.

quant-ph↗

arXiv2012

Spatially dependent decoherence and anomalous diffussion of quantum walks

We analyze the long time behavior of a discrete time quantum walk subject to decoherence with a strong spatial dependence, acting on one half of the lattice. We show that, except for limiting cases on the decoherence parameter, the quantum walk at late times behaves sub-ballistically, meaning that the characteristic features of the quantum walk are not completely spoiled. Contrarily to expectations, the asymptotic behavior is non Markovian, and depends on the amount of decoherence. This feature can be clearly shown on the long time value of the Generalized Chiral Distribution (GCD).

quant-ph↗

arXiv2012

Super-bunched bright squeezed vacuum state

In this paper we experimentally study the statistical properties of a bright squeezed vacuum state containing up to 10^13 photons per mode (10 uJ per pulse), produced via high gain parametric down conversion (PDC). The effects of bunching and superbunching of photons were observed for a single mode PDC radiation by second-order intensity correlation function measurements with analog detectors.

quant-ph↗

arXiv2011

The impact of SuperB on flavour physics

This report provides a succinct summary of the physics programme of SuperB, and describes that potential in the context of experiments making measurements in flavour physics over the next 10 to 20 years. Detailed comparisons are made with Belle II and LHCb, the other B physics experiments that will run in this decade. SuperB will play a crucial role in defining the landscape of flavour physics over the next 20 years.

hep-ex↗

arXiv2011

Analytic behavior of the QED polarizability function at finite temperature

We revisit the analytical properties of the static quasi-photon polarizability function for an electron gas at finite temperature, in connection with the existence of Friedel oscillations in the potential created by an impurity. In contrast with the zero temperature case, where the polarizability is an analytical function, except for the two branch cuts which are responsible for Friedel oscillations, at finite temperature the corresponding function is not analytical, in spite of becoming continuous everywhere on the complex plane. This effect produces, as a result, the survival of the oscillatory behavior of the potential. We calculate the potential at large distances, and relate the calculation to the non-analytical properties of the polarizability.

math-ph↗

arXiv2009

Information of a qubit interacting with a multilevel environment

We consider the interaction of a small quantum system (a qubit) with a structured environment consisting on many levels. The qubit will experience a decoherence process, which implies that its initial information will be transferred to the environment. We investigate how this information is distributed on a given subset of levels as a function of its size, using the mutual information between both entities, in the spirit of the partial information plots studied by Zurek. In this case we observe some differences, which arise from the fact that we are partitioning just one quantum system, and not a collection of them. However some similar features, like a redundancy (in the sense that a given amount of information is shared by many subsets), which increases with the size of the environment, are also found here.

quant-ph↗

arXiv2009

Measurement of the angle alpha at BABAR

We present recent measurements of the CKM angle alpha using data collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider at the SLAC National Accelerator Laboratory, operating at the Upsilon(4S) resonance. We present constraints on alpha from B->pipi, B->rhorho and B->rhopi decays.

hep-ex↗

arXiv2009

Hilbert Space Average Method and adiabatic quantum search

We discuss some aspects related to the so-called Hilbert space Average Method, as an alternative to describe the dynamics of open quantum systems. First we present a derivation of the method which does not make use of the algebra satisfied by the operators involved in the dynamics, and extend the method to systems subject to a Hamiltonian that changes with time. Next we examine the performance of the adiabatic quantum search algorithm with a particular model for the environment. We relate our results to the criteria discussed in the literature for the validity of the above-mentioned method for similar environments.

quant-ph↗

arXiv2007

Nonlinear optical Galton board

We generalize the concept of optical Galton board (OGB), first proposed by Bouwmeester et al. {[}Phys. Rev. A \textbf{61}, 013410 (2000)], by introducing the possibility of nonlinear self--phase modulation on the wavefunction during the walker evolution. If the original Galton board illustrates classical diffusion, the OGB, which can be understood as a grid of Landau--Zener crossings, illustrates the influence of interference on diffusion, and is closely connected with the quantum walk. Our nonlinear generalization of the OGB shows new phenomena, the most striking of which is the formation of non-dispersive pulses in the field distribution (soliton--like structures). These exhibit a variety of dynamical behaviors, including ballistic motion, dynamical localization, non--elastic collisions and chaotic behavior, in the sense that the dynamics is very sensitive to the nonlinearity strength.

quant-ph↗

arXiv2007

Non adiabatic quantum search algorithms

We present two new continuous time quantum search algorithms similar to the adiabatic search algorithm, but now without an adiabatic evolution. We find that both algorithms work for a wide range of values of the parameters of the Hamiltonian, and one of them has, as an additional feature that, for values of time larger than a characteristic one, it will converge to a state which can be close to the searched state.

quant-ph↗

arXiv2006

Black Hole evaporation in a thermalized final-state projection model

We propose a modified version of the Horowitz-Maldacena final-state boundary condition based upon a matter-radiation thermalization hypothesis on the Black Hole interior, which translates into a particular entangled state with thermal Schmidt coefficients. We investigate the consequences of this proposal for matter entering the horizon, as described by a Canonical density matrix characterized by the matter temperature $T$. The emitted radiation is explicitly calculated and is shown to follow a thermal spectrum with an effective temperature $T_{eff}$. We analyse the evaporation process in the quasi-static approximation, highlighting important differences in the late stages with respect to the usual semiclassical evolution, and calculate the fidelity of the emitted Hawking radiation relative to the infalling matter.

hep-th↗

arXiv2006

Neutrino emission due to Cooper pairing in neutron stars

Neutrino emission caused by Cooper pairing of baryons in neutron stars is recalculated by accurately taking into account for conservation of the vector weak current. The vector current contribution to the neutrino emissivity is found to be several orders of magnitude smaller than that obtained before by different authors. Therefore, the neutrino energy losses due to singlet-state pairing of baryons can in practice be neglected in simulations of neutron star cooling. This makes negligible the neutrino radiation from pairing of protons or hyperons. The neutrino radiation from triplet pairing takes place through axial weak currents. For these states, when the total momentum projection is $m_{j}=0$, the vanishing of the vector weak current contribution results in the suppression of the neutrino energy losses by about 25%. The neutrino emissivity due to triplet pairing with $| m_{j}| =2$ is suppressed by about a factor of 3, caused by the collective contribution of spin-density fluctuations in the condensate.

astro-ph↗

arXiv2006

Vector current conservation and neutrino emission from singlet-paired baryons in neutron stars

Neutrino emission caused by singlet Cooper pairing of baryons in neutron stars is recalculated by accurately taking into account for conservation of the vector weak currents. The neutrino emissivity via the vector weak currents is found to be several orders of magnitude smaller than that obtained before by different authors. This makes unimportant the neutrino radiation from singlet pairing of protons or hyperons.

astro-ph↗