Decision-Feedback Detection Strategy for Nonlinear Frequency-Division Multiplexing

By exploiting a causality property of the nonlinear Fourier transform, a novel decision-feedback detection strategy for nonlinear frequency-division multiplexing (NFDM) systems is introduced. The performance of the proposed strategy is investigated both by simulations and by theoretical bounds and approximations, showing that it achieves a considerable performance improvement compared to previously adopted techniques in terms of Q-factor. The obtained improvement demonstrates that, by tailoring the detection strategy to the peculiar properties of the nonlinear Fourier transform, it is possible to boost the performance of NFDM systems and overcome current limitations imposed by the use of more conventional detection techniques suitable for the linear regime

Direct Connection between Mott Insulator and d-Wave High-Temperature Superconductor Revealed by Continuous Evolution of Self-Energy Poles

The high-temperature superconductivity in copper oxides emerges when carriers are doped into the parent Mott insulator. This well-established fact has, however, eluded a microscopic explanation. Here we show that the missing link is the self-energy pole in the energy-momentum space. Its continuous evolution with doping directly connects the Mott insulator and high-temperature superconductivity. We show this by numerically studying the extremely small doping region close to the Mott insulating phase in a standard model for cuprates, the two-dimensional Hubbard model. We first identify two relevant self-energy structures in the Mott insulator; the pole generating the Mott gap and a relatively broad peak generating the so-called waterfall structure, which is another consequence of strong correlations present in the Mott insulator. We next reveal that either the Mott-gap pole or the waterfall structure (the feature at the energy closer to the Fermi level) directly transforms itself into another self-energy pole at the same energy and momentum when the system is doped with carriers. The anomalous self-energy yielding the superconductivity is simultaneously born exactly at this energy-momentum point. Thus created self-energy pole, interpreted as arising from a hidden fermionic excitation, continuously evolves upon further doping and considerably enhances the superconductivity. Above the critical temperature, the same self-energy pole generates a pseudogap in the normal state. We thus elucidate a unified Mott-physics mechanism, where the self-energy structure inherent to the Mott insulator directly gives birth to both the high-temperature superconductivity and pseudogap.Comment: 14 pages, 18 figure

Numerical Methods for the Inverse Nonlinear Fourier Transform

We introduce a new numerical method for the computation of the inverse nonlinear Fourier transform and compare its computational complexity and accuracy to those of other methods available in the literature. For a given accuracy, the proposed method requires the lowest number of operationsComment: To be presented at the Tyrrhenian International Workshop on Digital Communications (TIWDC) 201

Why Noise and Dispersion may Seriously Hamper Nonlinear Frequency-Division Multiplexing

The performance of optical fiber systems based on nonlinear frequency-division multiplexing (NFDM) or on more conventional transmission techniques is compared through numerical simulations. Some critical issues affecting NFDM systems-namely, the strict requirements needed to avoid burst interaction due to signal dispersion and the unfavorable dependence of performance on burst length-are investigated, highlighting their potentially disruptive effect in terms of spectral efficiency. Two digital processing techniques are finally proposed to halve the guard time between NFDM symbol bursts and reduce the size of the processing window at the receiver, increasing spectral efficiency and reducing computational complexity.Comment: The manuscript has been submitted to Photonics Technology Letters for publicatio

A Novel Detection Strategy for Nonlinear Frequency-Division Multiplexing

A novel decision feedback detection strategy exploiting a causality property of the nonlinear Fourier transform is introduced. The novel strategy achieves a considerable performance improvement compared to previously adopted strategies in terms of Q-factor.Comment: The work has been submitted to the Optical Fiber Communication (OFC) Conference 201

T=0 heavy fermion quantum critical point as an orbital selective Mott transition

We describe the T=0 quantum phase transition in heavy fermion systems as an orbital selective Mott transition (OSMT) using a cluster extension of dynamical mean field theory. This transition is characterized by the emergence of a new intermediate energy scale corresponding to the opening of a pseudogap and the vanishing of the low-energy hybridization between light and heavy electrons. We identify the fingerprint of Mott physics in heavy electron systems with the appearance of surfaces in momentum space where the self-energy diverges and we derive experimental consequences of this scenario for photoemission, compressibility, optical conductivity, susceptibility and specific heat.Comment: 4 pages, 3 figures. Published versio

Cellular Dynamical Mean Field Theory of the Periodic Anderson Model

We develop a cluster dynamical mean field theory of the periodic Anderson model in three dimensions, taking a cluster of two sites as a basic reference frame. The mean field theory displays the basic features of the Doniach phase diagram: a paramagnetic Fermi liquid state, an antiferromagnetic state and a transition between them. In contrast with spin density wave theories, the transition is accompanied by a large increase of the effective mass everywhere on the Fermi surface and a substantial change of the Fermi surface shape across the transition. To understand the nature and the origin of the phases near the transition, we investigate the paramagnetic solution underlying the antiferromagnetic state, and identify the transition as a point where the $f$ electrons decouple from the conduction electrons undergoing an orbitally selective Mott transition. This point turns out to be intimately related to the two impurity Kondo model quantum critical point. In this regime, non local correlations become important and result in significant changes in the photoemission spectra and the de Haas-van Alphen frequencies. The transition involves considerable $f$ spectral weight transfer from the Fermi level to its immediate vicinity, rather than to the Hubbard bands as in single site DMFT.Comment: 7 pages, 7 figure