1,721,606 research outputs found
Challenges to Sustainable Knowledge Transfer in cross-cultural Teacher Education
Full text linkThe policy of transferring international educational knowledge across cultural and geographical borders has become a common practice for the international community, especially after the 1990 Education for All (EFA) agreement. Egypt is complying with this policy by relying on teacher education to transfer international knowledge to more traditional sectors, in an attempt to bridge the quality gap in its national (Early Childhood) education system. However, according to many scholars, knowledge transfer is not a straightforward process, as educational settings and knowledge are autopoietic, value-laden and idiosyncratic. At the same time, constructivist and reflective models of teacher education, which claim to foster sustainable knowledge transfer, are becoming increasingly popular. ‘Sustainable transfer’ is defined here as the process by which international knowledge is successfully accommodated within local educational settings. This study investigates the circumstances which may hinder or facilitate the transfer of international knowledge to local developing realities within the framework of constructivist and reflective teacher education, in order to understand the sustainability of this international policy
Gently modulating opto-mechanical systems
No full textWe introduce a framework of optomechanical systems that are driven with a mildly amplitude-modulated light field, but that are not subject to classical feedback or squeezed input light. We find that in such a system one can achieve large degrees of squeezing of a mechanical micromirror-signifying quantum properties of optomechanical systems- without the need of any feedback and control, and within parameters reasonable in experimental settings. Entanglement dynamics is shown of states following classical quasiperiodic orbits in their first moments. We discuss the complex time dependence of the modes of a cavity-light field and a mechanical mode in phase space. Such settings give rise to certifiable quantum properties within experimental conditions feasible with present technology
Quantum optomechanical piston engines powered by heat
No full textWe study two different models of optomechanical systems where a temperature
gradient between two radiation baths is exploited for inducing self-sustained
coherent oscillations of a mechanical resonator. Viewed from a thermodynamic
perspective, such systems represent quantum instances of self-contained thermal
machines converting heat into a periodic mechanical motion and thus they can be
interpreted as nano-scale analogues of macroscopic piston engines. Our models
are potentially suitable for testing fundamental aspects of quantum
thermodynamics in the laboratory and for applications in energy efficient
nanotechnology
Classical capacity of Gaussian thermal memory channels
Full text linkThe classical capacity of phase-invariant Gaussian channels has been recently determined under the assumption that such channels are memoryless. In this work we generalize this result by deriving the classical capacity of a model of quantum memory channel, in which the output states depend on the previous input states. In particular we extend the analysis of Lupo et al. [Phys. Rev. Lett. 104, 030501 (2010) and Phys. Rev. A 82, 032312 (2010)] from quantum limited channels to thermal attenuators and thermal amplifiers. Our result applies in many situations in which the physical communication channel is affected by nonzero memory and by thermal noise.The classical capacity of phase-invariant Gaussian channels has been recently determined under the assumption that such channels are memoryless. In this work we generalize this result by deriving the classical capacity of a model of quantum memory channel, in which the output states depend on the previous input states. In particular we extend the analysis of Lupo et al. [Phys. Rev. Lett. 104, 030501 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.030501 and Phys. Rev. A 82, 032312 (2010)PLRAAN1050-294710.1103/PhysRevA.82.032312] from quantum limited channels to thermal attenuators and thermal amplifiers. Our result applies in many situations in which the physical communication channel is affected by nonzero memory and by thermal noise
Majorization and additivity for multimode bosonic Gaussian channels
No full textRecently, the longstanding Gaussian optimizer conjecture was proven for
bosonic Gaussian gauge-covariant or contravariant channels in the work of
Giovannetti, Holevo and Garcia-Patron [3]. In the paper of Mari, Giovannetti
and Holevo [11] this result was strengthened for one-mode channels by
establishing that the output for the vacuum or coherent input majorizes the
output for any other input.
In the present paper we give the multimode extension of the result of [11],
including sufficient conditions under which the coherent states are the only
optimizers. We also discuss direct implications of this multimode majorization
result to the positive solution of the additivity problem for the Gaussian
channels. In particular, we demonstrate the additivity of the output Renyi
entropies of arbitrary order p>1. Finally, we present an alternative derivation
of a majorization property of Glauber's coherent states by Lieb and Solovej
[10], basing on the method of the work [3]
Coherent-state discrimination via nonheralded probabilistic amplification
Full text linkA scheme for the detection of low-intensity optical coherent signals was studied which uses a probabilistic amplifier operated in the nonheralded version as the underlying nonlinear operation to improve the detection efficiency. This approach allows us to improve the statistics by keeping track of all possible outcomes of the amplification stage (including failures). When compared with an optimized Kennedy receiver, the resulting discrimination success probability we obtain presents a gain up to â1⁄41.85% and it approaches the Helstrom bound appreciably faster than the Dolinar receiver when employed in an adaptive strategy. We also notice that the advantages obtained can ultimately be associated with the fact that, in the high-gain limit, the nonheralded version of the probabilistic amplifier induces a partial dephasing which preserves quantum coherence among low-energy eigenvectors while removing it elsewhere. A proposal to realize such a transformation based on an optical cavity implementation is presented
Narrow bounds for the quantum capacity of thermal attenuators
Full text linkThermal attenuator channels model the decoherence of quantum systems interacting with a thermal bath, e.g., a two-level system subject to thermal noise and an electromagnetic signal traveling through a fiber or in free-space. Hence determining the quantum capacity of these channels is an outstanding open problem for quantum computation and communication. Here we derive several upper bounds on the quantum capacity of qubit and bosonic thermal attenuators. We introduce an extended version of such channels which is degradable and hence has a single-letter quantum capacity, bounding that of the original thermal attenuators. Another bound for bosonic attenuators is given by the bottleneck inequality applied to a particular channel decomposition. With respect to previously known bounds we report better results in a broad range of attenuation and noise: we can now approximate the quantum capacity up to a negligible uncertainty for most practical applications, e.g., for low thermal noise
Experiments testing macroscopic quantum superpositions must be slow
Full text linkWe consider a thought experiment where the preparation of a macroscopically massive or charged particle in a quantum superposition and the associated dynamics of a distant test particle apparently allow for superluminal communication. We give a solution to the paradox which is based on the following fundamental principle: any local experiment, discriminating a coherent superposition from an incoherent statistical mixture, necessarily requires a minimum time proportional to the mass (or charge) of the system. For a charged particle, we consider two examples of such experiments, and show that they are both consistent with the previous limitation. In the first, the measurement requires to accelerate the charge, that can entangle with the emitted photons. In the second, the limitation can be ascribed to the quantum vacuum fluctuations of the electromagnetic field. On the other hand, when applied to massive particles our result provides an indirect evidence for the existence of gravitational vacuum fluctuations and for the possibility of entangling a particle with quantum gravitational radiation
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