Omar P. Vilela Neto

Neural Network Simulation and Evolutionary Synthesis of QCA Circuits

CMOS technology miniaturization limits have promoted research on new alternatives which can keep the technologically advanced level of the last decades. Quantum-dot cellular automata (QCA) is a new technology in the nanometer scale that has been considered as one of these alternatives. QCA have a large potential in the development of circuits with high space density and low heat dissipation and allow the development of faster computers with lower power consumption. Differently from conventional technologies, QCA do not codify information by means of electric current flow, but rather by the configuration of electrical charges in the interior of the cells. The Coulomb interaction between cells is responsible for the flow of information. This paper proposes the use of computational intelligence techniques in the simulation and in the automatic synthesis of QCA circuits. The first results show that these techniques may play an important role in this research area since they are capable of simulating efficiently and fast, synthesizing optimized circuits with a reduced number of cells. Such optimization reduces the possibility of failures and guarantees higher speed

NanoRouter: A Quantum-dot Cellular Automata Design

We present NanoRouter, a new router architecture implemented as a quantum-dot cellular automata (QCA). A router is a key component in the Internet core. It allows packets to be transferred in the Internet. QCA is a promising nanoscale technology where components have nano size, ultra-low power consumption and could have a clock rate on the terahertz range. In a bottom-up approach, we first describe the building blocks that compose NanoRouter such as crossbar, demux and parallel-to-serial converter and then describe the full architecture. We demonstrate the functionality, test and validate the proposed architecture and provided performance evaluations of NanoRouter. This new router architecture can increase the speed of the Internet core.

USE: A Universal, Scalable, and Efficient Clocking Scheme for QCA

Quantum-dot cellular automata (QCA) is an emerging technology, conceived in face of nanoscale limitations of CMOS circuits, with exceptional integration density, impressive switching frequency, and remarkable low-power characteristics. Several of the current challenges toward the progress of QCA technology is related to the automation of the design process and integration into existing design flows. In this regard, this paper proposes the universal, scalable, efficient (USE), and easily manufacturable clocking scheme. It solves one of the most limiting factors of existing clock schemes, the implementation of feedback paths and easy routing of QCA-based circuits. Consequently, USE facilitates considerably the development of standard cell libraries and design tools for this technology, besides avoiding thermodynamics problems. Case studies presented in this paper reveal an area reduction of up to factor 5 and delay decrease by up to factor 3 in comparison with an existing advanced clocking scheme.

Robust Serial Nanocommunication With QCA

We present a serial communication system implemented as quantum-dot cellular automata (QCA). QCA is a promising alternative to the current CMOS technology. It can be implemented at the nanoscale, reaching ultra-low power consumption and high clock rate. Communication systems are important in current computer systems and it is expected to be even more important in near future. Although QCA has been widely studied in the development of logic circuits, there are few studies applying this promising technology to the design of communication systems. In a bottom-up approach, we describe the parallel-to-serial and serial-to-parallel converters, which are essential to the serial communication. We also propose and present components for robust communication, such as QCA circuits for Hamming code and parity checker. We demonstrate the functionality, test and validate the proposed architectures using QCADesigner simulator. Due to the importance of communication systems, this study is central in consolidating QCA as a possible CMOS substitute.

Theoretical and experimental study of negative LiF clusters produced by fast ion impact on a polycrystalline 7LiF target.

The emission of negative cluster ions produced by the impact of approximately 60 MeV (252)Cf fission fragments on a (7)LiF polycrystalline target is analyzed. The negative ion mass spectrum is dominated by the ((7)LiF)(n)F(-) series, n = 1 to approximately 30. The desorption yield distribution of the ((7)LiF)(n)F(-) members has a maximum at n = 2 and then decreases as the sum of two exponentials whose decay parameters are k(Fast) = 0.9 and k(Slow) = 0.08. These k values are the same as those observed for the positive series and close to others obtained for condensed gas targets. Relative cluster ion stabilities, deduced from the experimental ion abundances for the (LiF)(n)F(-) series, are proposed to be correlated with theoretical structures according to their internal energy by using the deviation plot (D-plot) methodology. A pool of candidate cluster structures was generated using a genetic algorithm and further analyzed and optimized using density functional theory (DFT) with the hybrid functional B3LYP (DFT/B3LYP) and Moller-Plesset perturbation theory (MP2). For the small clusters (n = 1 to 2), the most stable structures are found to be linear, whereas the larger clusters (n = 4 to 6) present cubic or polyhedral structures. Fragmentation energies, ionization potentials, and relative stabilities are reported for the most abundant families of the (LiF)(n)F(-) and (LiF)(n)(-) series.

TCAM/CAM-QCA: (Ternary) Content Addressable Memory using Quantum-dot Cellular Automata

Abstract This paper describes a Content Addressable Memory (CAM) architecture and its ternary variant called Ternary Content Addressable Memory (TCAM) using the Quantum-dot Cellular Automata (QCA). QCA is an alternative to the current integrated circuit (CMOS) paradigm based on the characteristics of confinement and mutual repulsion between electrons. It is expected to run with clocks in high frequency (in THz order), in nanometers scale and with very low energy consumption. First, this work presents the basic building blocks (1-bit memory cell, array of memory cells, ternary memory line and encoder). Then, we describe the complete TCAM and CAM architectures. Finally, the proposed architectures are tested and validated using QCADesigner simulator, attesting their functionalities. If QCA consolidates as a possible CMOS substitute, this study can impact the design of future components that uses TCAM and CAM such as routers and switches respectively.

A Quantum-Dot Cellular Automata Processor Design

This paper describes the complete implementation of a robust SUBNEG (subtract and branch if negative) processor using quantum-dot cellular automata (QCA) technology. A processor is the basic unit in computer systems which is responsable for performing the basic arithmetic, logic, and input/output operations. QCA is a promising nanotechnology where components have nano size, ultra-low power consumption and could have a clock rate on terahertz rate. The architecture of our processor was inspired by the one used on the first carbon nanotube computer. We used this work as reference because both nanotechnology (the carbon nanotube and QCA) are promising and able to overcome the limits of current CMOS technology. Our work is the first implementation of a SUBNEG processor in QCA technology and, moreover, satisfies all constraints in order to make it robust. In a bottom-up approach, we first describe the building blocks that compose the QCA SUBNEG processor such as the ALU and the data and instruction memories. Next, we present the processor architecture. Lastly, we describe tests and performance evaluation of the QCA SUBNEG processor.

Towards reversible QCA computers: Reversible gates and ALU

This work presents a novel implementation of reversible gates and reversible ALU, all based in quantum-dot cellular automata (QCA). QCA has been considered as an alternative for field-effect transistors due to its quite small size (nanometers), ultra-low power consumption and clock rate (terahertz range). On the other hand, reversible computation is a new paradigm where all logic operations can be performed in an invertible way. This feature is important to different technologies, such as quantum computing, adiabatic circuits, low power computation, etc. Regarding low power consumption, QCA has been seen as a promising technology for approaching the thermodynamic limit of computation and this work focus on designing a QCA reversible ALU in order to go beyond that limit, bridging the gap between QCA technology and reversible components. In a bottom-up approach, we first discuss QCA reversible gates and a few design choices. We also present the ALUs QCA design, demonstrate the functionality, test and validate the proposed architecture using QCADesigner simulator. Due to the importance of these new computational paradigms, this study is central in consolidating possible emerging technologies.

A parallel evolutionary algorithm to search for global minima geometries of heterogeneous ab initio atomic clusters

In this work we present a parallel evolutionary algorithm applied to the search of the lowest-energy structures of heterogeneous atomic clusters. A new and improved crossover operator is proposed in order to always ensure the creation of new clusters with the same number of atomic elements. The approach proposed proved to be efficient and fast as all cluster calculations were performed by an ab initio quantum mechanics method, which is computationally expensive. Results of our search, obtained using the proposed approach, have been compared with previous calculations, and the efficiency has been confirmed, as we were able to find the global minimum and propose a wide number of new isomers of low-energy. Specifically, we addressed the problem to deal with clusters of lithium and fluorine atoms. However, the proposed algorithm can be extended to all kind of atomic and molecular clusters.

Analysis of the Magnetostatic Energy of Chains of Single-Domain Nanomagnets for Logic Gates

Nanomagnet logic (NML) circuits are magnetic field-coupled interacting structures built up from nanoscaled magnets to perform logic operations. The bistable character of nanomagnets’ magnetization is associated with “0” and “1” logic states, which may be used to perform Boolean operations. In this paper, we first investigate the limits of single-domain magnetic structure in modeling the magnetostatic energy of particles of several polyhedron shapes. The model, which is based on the evaluation of multidimensional integrals through the Monte Carlo method, includes the demagnetizing energy of individual magnetic specimens and the dipolar coupling between two or more nanomagnets. The accuracy and the limits of the model are evaluated through comparison with a well-established numerical micromagnetic solver. The magnetostatic behavior for several configurations of horizontal chain of interacting nanomagnets (NML wire) is investigated. Rectangular nanomagnets present weak dipolar antiferromagnetic (AF) coupling that may result in error during information propagation across the chain. We examine a novel wire structure formed by a sequence of different slanted nanomagnets that yield strong dipolar coupling. For this system, error during information propagation is very unlikely, since the magnetic energy of the particles has single global minima corresponding to stable AF alignment. The proposed model can be readily applied as a tool for the study of advanced NML circuits and systems.