21,897 research outputs found
Bypassing state initialization in Hamiltonian tomography on spin-chains
We provide an extensive discussion on a scheme for Hamiltonian tomography of
a spin-chain model that does not require state initialization [Phys. Rev. Lett.
102, 187203 (2009)]. The method has spurred the attention of the physics
community interested in indirect acquisition of information on the dynamics of
quantum many-body systems and represents a genuine instance of a
control-limited quantum protocol.Comment: 7 pages, 2 figures, RevTeX
Nested entangled states for distributed quantum channels
We find a coupling-strength configuration for a linear chain of N spins which
gives rise to simultaneous multiple Bell states. We suggest a way such an
interesting entanglement pattern can be used in order to distribute maximally
entangled channels to remote locations and generate multipartite entanglement
with a minimum-control approach. Our proposal thus provides a way to achieve
the core resources in distributed information processing. The schemes we
describe can be efficiently tested in chains of coupled cavities interacting
with three-level atoms.Comment: 4 pages, 2 figures, RevTeX
X-band noise temperature effects of rain on DSN antenna feedhorns
Simulated rain tests were carried out to determine the noise temperature contribution of liquid water adhering to the aperture cover material on both a standard DSN X-band feedhorn and on an S/X-band common aperture feedhorn. It was found that for the particular common aperture feedhorn tested, system noise temperature increases were much greater when the plastic horn cover material was old and weathered than when it was new. The age and condition of the aperture cover material is believed to be a major factor in the amount of degradation experienced by a telecommunications system during rain events
Quantum state transfer via temporal kicking of information
We propose a strategy for perfect state transfer in spin chains based on the
use of an unmodulated coupling Hamiltonian whose coefficients are explicitly
time dependent. We show that, if specific and non-demanding conditions are
satisfied by the temporal behavior of the coupling strengths, our model allows
perfect state transfer. The paradigma put forward by our proposal holds the
promises to set an alternative standard to the use of clever encoding and
coupling-strength engineering for perfect state transfer.Comment: 7 pages, 7 figures, RevTeX
Information-flux approach to multiple-spin dynamics
We introduce and formalize the concept of information flux in a many-body
register as the influence that the dynamics of a specific element receive from
any other element of the register. By quantifying the information flux in a
protocol, we can design the most appropriate initial state of the system and,
noticeably, the distribution of coupling strengths among the parts of the
register itself. The intuitive nature of this tool and its flexibility, which
allow for easily manageable numerical approaches when analytic expressions are
not straightforward, are greatly useful in interacting many-body systems such
as quantum spin chains. We illustrate the use of this concept in quantum
cloning and quantum state transfer and we also sketch its extension to
non-unitary dynamics.Comment: 7 pages, 4 figures, RevTeX
Qubit-oscillator systems in the ultrastrong-coupling regime and their potential for preparing nonclassical states
We consider a system composed of a two-level system (i.e. a qubit) and a
harmonic oscillator in the ultrastrong-coupling regime, where the coupling
strength is comparable to the qubit and oscillator energy scales. Special
emphasis is placed on the possibility of preparing nonclassical states in this
system. These nonclassical states include squeezed states, Schrodinger-cat
states and entangled states. We start by comparing the predictions of a number
of analytical methods that can be used to describe the system under different
assumptions, thus analyzing the properties of the system in various parameter
regimes. We then examine the ground state of the system and analyze its
nonclassical properties. We finally discuss some questions related to the
possible experimental observation of the nonclassical states and the effect of
decoherence.Comment: 19 pages (two-column), 11 figure
Measurement of ortho-Positronium Properties in Liquid Scintillators
Pulse shape discrimination in liquid scintillator detectors is a
well-established technique for the discrimination of heavy particles from light
particles. Nonetheless, it is not efficient in the separation of electrons and
positrons, as they give rise to indistinguishable scintillator responses. This
inefficiency can be overtaken through the exploitation of the formation of
ortho-Positronium (o-Ps), which alters the time profile of light pulses induced
by positrons.
We characterized the o-Ps properties in the most commonly used liquid
scintillators, i.e. PC, PXE, LAB, OIL and PC + PPO. In addition, we studied the
effects of scintillator doping on the o-Ps properties for dopants currently
used in neutrino experiments, Gd and Nd. Further measurements for Li-loaded and
Tl-loaded liquid scintillators are foreseen. We found that the o-Ps properties
are suitable for enhancing the electron-positron discrimination.Comment: 4 pages, 1 figure. Contribution to proceedings of the Low
Radioactivity Techniques 2013 Workshop at LNGS, Assergi (AQ), Italy, April
10-12 201
Lower limit on the achievable temperature in resonator-based sideband cooling
A resonator can be effectively used as a cooler for another linear oscillator
with a much smaller frequency. A huge cooling effect, which could be used to
cool a mechanical oscillator below the energy of quantum fluctuations, has been
predicted by several authors. However, here we show that there is a lower limit
T* on the achievable temperature that was not considered in previous works and
can be higher than the quantum limit in realistic experimental realizations. We
also point out that the decay rate of the resonator, which previous studies
stress should be small, must be larger than the decay rate of the cooled
oscillator for effective cooling.Comment: 6 pages, 4 figures, uses psfra
Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system
We theoretically investigate the thermoelectric properties of a
spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized
with an STM tip. Such a setup is treated within the single-impurity Anderson
model in combination with the atomic approach for the Green's functions. Due to
the spin dependence of the Fermi wavenumbers the electrical and thermal
conductances, together with thermopower and Lorenz number reveal beating
patterns as function of the STM tip position in the Kondo regime. In
particular, by tuning the lateral displacement of the tip with respect to the
adatom vicinity, the temperature and the position of the adatom level, one can
change the sign of the Seebeck coefficient through charge and spin. This opens
a possibility of the microscopic control of the heat flux analogously to that
established for the electrical current
Resposta aos movimentos jihadistas Somali e Mali: Que lições para Moçambique?
AbstractSince 2017, Mozambique’s Cabo Delgado province has witnessed an unprecedented level of violence attributed to jihadist movements. The security threat, instability and deteriorating humanitarian situation in the area has attracted the attention of regional and international actors. The aim of this article is twofold. On the one hand, it discusses the response to jihadist movements in Somalia and Mali in order to explain and contextualize external interventions in Mozambique. On the other hand, it explores the extent of lessons-learned based on the evidence from Somalia and Mali. Specifically, it considers how such interventions may help shade light towards a better understanding of the origin and evolution of Mozambican-based jihadist movement and the possible responses from external actors. The arguments are guided by a post-liberal approach. However, drawing from the relative deprivation theory, the article also focuses on the economic and social exclusion experienced in Cabo Delgado province and highlights the possible underlying root-causes of the current situation. As a main conclusion, lessons learned from stabilization and counterinsurgency interventions in Somalia and Mali must be an integral part of the responses to the Mozambique conflict.
Keywords: external interventions; jihadist movements; Mali; Mozambique; post-liberal; Somaliainfo:eu-repo/semantics/publishedVersio
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