Split current quantum cellular automata: device and logic gates

Missing-cell defects in QCA wires: The ground and excited electronic states perspectives

Quantum cellular automata (QCA) technology is a nanotechnology provides a very different computation platform than traditional CMOS, in which polarization of electrons indicates the digital information. This paper discusses about the quantum cellular automata complex gate structure consist of 3, 4 and 5 input majority gates. Multi input complex gates can be constructed with the single QCA structure that can be configured in to Boolean functions and logic gates. We have also constructed product of sum and sum of product representation and other different Boolean functions. QCA circuits are simulated using QCAdesinger tool and waveforms are presented. We also validate the constructed structure by building combination al circuits like comparators etc. A single fixed QCA structure is useful for building module in QCA FPGA and ASIC applications.

In this review we shortly summarize in an accessible way the physical and nanoscale material science aspects of the promising field of molecular quantum cellular automata (QCA). QCA is a revolutionary paradigm in quantum electronics with promising application in the conceptually new computing scheme which can be referred to as “computing with molecules”. This scheme of devices have vitally important advantages compared with conventional schemes of quantum computing in which the binary information is stored in the eigenvectors of a two‐level quantum system and therefore their practical application is strongly limited by the requirement of coherence. Molecular QCA promise nanometer‐scale units with ultra‐high device densities, as well as room temperature operation with extremely small heat release. Molecular materials provide at the same time options to control the key properties of the active molecules by chemical means. Hereunder we summarize the background of the electronic and vibronic problems in QCA cells represented by the tetrameric mixed‐valence (MV) complexes and organic molecules proposed for implementation as four‐site molecular QCA. We discuss the basic model of the molecular cell that include the following ingredients: 1) intracell Coulomb repulsion energy of the electrons in different electronic distributions among the redox sites; 2) electron transfer between redox sites which changes electronic distributions; 3) interaction of the itinerant electrons with molecular vibrations which is referred to as the vibronic interactions; 4) intercell Coulomb interaction by mean of which the binary information is transmitted from cell to cell. On the basis of this model we will study the cell polarization, adiabatic picture of the switching cycle describing interaction between the “input” and “output” molecular cells, non‐linear cell‐cell response function whose shape describes the action of molecular logic gates. Along with developed and current problems, we discuss new challenging trends of research in this fascinating area.

In the past few years, CMOS semiconductor has been a growing and evolving technology in VLSI. However, due to the scaling issue and some other constraints like heat generation, high power consumption QCA (quantum cellular automata) emerged as an alternate and enhanced solution that provides a new technique of computing than CMOS in recent years. QCA is highly effective in implementing both Irreversible and Reversible logic, which has been shown to be incredibly efficient in terms of power consumption. A novel technique to data encryption called as SCV (select, cross, and variation) is demonstrated in this paper, which is based on ASCII to binary conversion and uses reversible logic. The data security procedure is aided by implementing SCV logic in reversible logic. Using Fredkin gate, it is built in QCA. QCADesigner tool has been used here for design and verification purposes. Total 80 cell counts and 0.14 μm 2 area are required. The theoretical data and the simulation results are the same as the intended circuit. Comparison to previous QCA architectural features is featured.

Our interest in this article is prompted by the vibronic problem of charge polarized states in the four-dot molecular quantum cellular automata (mQCA), a paradigm for nanoelectronics, in which binary information is encoded in charge configuration of the mQCA cell. Here, we report the evaluation of the electronic levels and adiabatic potentials of mixed-valence (MV) tetra-ruthenium (2Ru(ii) + 2Ru(iii)) derivatives (assembled as two coupled Creutz-Taube complexes) for which molecular implementations of quantum cellular automata (QCA) was proposed. The cell based on this molecule includes two holes shared among four spinless sites and correspondingly we employ the model which takes into account the two relevant electron transfer processes (through the side and through the diagonal of the square) as well as the difference in Coulomb energies for different instant positions of localization of the hole pair. The combined Jahn-Teller (JT) and pseudo JT vibronic coupling is treated within the conventional Piepho-Krauzs-Schatz model adapted to a bi-electronic MV species with the square-planar topology. The adiabatic potentials are evaluated for the low lying Coulomb levels in which the antipodal sites are occupied, the case just actual for utilization in mQCA. The conditions for the vibronic self-trapping in spin-singlet and spin-triplet states are revealed in terms of the two actual transfer pathways parameters and the strength of the vibronic coupling. Spin related effects in degrees of the localization which are found for spin-singlet and spin-triplet states are discussed. The polarization of the cell is evaluated and we demonstrate how the partial delocalization caused by the joint action of the vibronic coupling and electron transfer processes influences polarization of a four-dot cell. The results obtained within the adiabatic approach are compared with those based on the numerical solution of the dynamic vibronic problem. Finally, the Coulomb interaction between the cells is considered and the influence of the vibronic coupling on the shape on the non-linear cell-cell response function is revealed.

We discuss the possibility of using mixed-valence (MV) dimers comprising paramagnetic metal ions as molecular cells for quantum cellular automata (QCA). Thus, we propose to combine the underlying idea behind the functionality of QCA of using the charge distributions to encode binary information with the additional functional options provided by the spin degrees of freedom. The multifunctional ("smart") cell is supposed to consist of multielectron MV dn-dn+1-type (1 ≤ n ≤ 8) dimers of transition metal ions as building blocks for composing bi-dimeric square planar cells for QCA. The theoretical model of such a cell involves the double exchange (DE), Heisenberg-Dirac-Van Vleck (HDVV) exchange, Coulomb repulsion between the two excess electrons belonging to different dimeric half-cells and also the vibronic coupling. Consideration is focused on the topical case in which the difference in Coulomb energies of the two excess electrons occupying nearest neighboring and distant positions significantly exceeds both the electron transfer integral and the vibronic energy. In this case the ground spin-state of the isolated square cell is shown to be the result of competition of the second-order DE producing a ferromagnetic effect and the HDVV exchange that is assumed to be antiferromagnetic. In order to reveal the functionality of the magnetic cells, the cell-cell response function is studied within the developed model. The interaction of the working cell with the polarized driver-cell is shown to produce an antiferromagnetic effect tending to suppress the ferromagnetic second-order DE. As a result, under some conditions the electric field of the driver cell is shown to force the working cell to exhibit spin-switching from the state with maximum dimeric spin values to that having minimal spin values.

We present a proposal for an experiment to demonstrate QCA (Quantum Cellular Automaton) functionality for a cell fabricated with silicon-on-insulator technology. The fundamental feature of a working QCA cell consists in the anticorrelated transition of electrons in the two pairs of dots forming the cell: we show how such a phenomenon can be detected from the appearance of a “locking” effect between the Coulomb Blockade current peaks relative to each pair. The proposed approach allows the detection of QCA action without the need for additional noninvasive charge detectors probing each dot. We have performed detailed numerical simulations on the basis of interdot capacitance values obtained from experimental data and determined the range of parameters within which the effect should be detectable.

Response functions used in crop simulation models are usually different for different physiological processes and cultivars, resulting in many unknown coefficients in the response functions. This is the case of African violet (Saintpaulia ionantha Wendl.), where a generalized temperature response for leaf growth and development has not been developed yet. The objective of this study was to develop a generalized nonlinear temperature response function for leaf appearance rate and leaf elongation rate in African violet. The nonlinear function has three coefficients, which are the cardinal temperatures (minimum, optimum, and maximum temperatures). These coefficients were defined as 10, 24, and 33ºC, based on the cardinal temperatures of other tropical species. Data of temperature response of leaf appearance rate and leaf elongation rate in African violet, cultivar Utah, at different light levels, which are from published research, were used as independent data for evaluating the performance of the nonlinear temperature response function. The results showed that a generalized nonlinear response function can be used to describe the temperature response of leaf growth and development in African violet. These results imply that a reduction in the number of input data required in African violet simulation models is possible.

Molecular quantum cellular automata (QCA) devices are typically based on the square planar two-electron mixed valence (MV) molecules playing the role of QCA cells. The functional properties of such cells are determined by the Coulomb repulsion between the two excess electrons, which stabilize antipodal charge configurations that encoding binary information. The inner sphere electron transfer of the excess electrons transforming different charge configurations into each other, as well as by the vibronic coupling, which tends to localize the mobile charges. Previously, the most topical and theoretically complex case of arbitrary Coulomb repulsion has been considered by implying essential restricting assumptions on the network of the electron transfer pathways. Therefore, the electron transfer occurring along the sides of the molecular square has been taken into account. Meanwhile, the effects of diagonal transfer have been discussed only for the limiting case of strong intracell Coulomb repulsion, which is peculiar to predominantly ionic compounds that are unlikely to be relevant to the MV cells. Here, we go beyond these simplifying assumptions and consider the general situation when all electron transfer pathways are involved, providing arbitrary interrelations between the key electronic and vibronic parameters. By solving the adiabatic and quantum-mechanical three-mode vibronic problems, we reveal the influence of electron transfer network topology on key properties of QCA, such as the stabilization of different spin-states in the free and interacting cells, the extent of localization of the pair of excess electrons, the shape of the cell-cell response functions, and the heat release necessarily occurring in the course of the non-adiabatic switching cycle.

We investigate the feasibility of an adiabatic logic scheme for cellular automaton systems recently proposed by Tóth and Lent [J. Appl. Phys. 85, 2977 (1999)], based on structured arrays of six-dot cells and on the use of a four-phase trapezoidal clock. With respect to the original quantum cellular automaton (QCA) concept, focused on ground state computation, a clocked scheme would have the advantage of being immune to the presence of metastable states and would allow pipelined operation, at the expense of additional complexity, due to the clock distribution circuitry. Based on realistic cell geometries and material systems, we have evaluated the obtainable switching times of QCA cells, and have determined the region in the parameter space that allows operation at a reasonable clock speed.

Quantum cellular automata (QCA) represents an emerging technology at the nanotechnology level. Nowadays, many applications of QCA technology are introduced and cryptography can be an interesting application of QCA technology. The original encryption algorithm for GSM was A5/1. Here, we have implemented the A5/1 stream cipher using QCA technology. Simulation results are obtained from QCADesigner software.

Non-linear signal response functions and their effects on the statistical and noise cancellation properties of isotope ratio measurements by multi-collector plasma mass spectrometry

Observables in nonlinear and multidimensional infrared spectroscopy may be calculated from nonlinear response functions. Numerical challenges associated with the fully quantum-mechanical calculation of these dynamical response functions motivate the development of semiclassical methods based on the numerical propagation of classical trajectories. The Herman-Kluk frozen Gaussian approximation to the quantum propagator has been demonstrated to produce accurate linear and third-order spectroscopic response functions for thermal ensembles of anharmonic oscillators. However, the direct application of this propagator to spectroscopic response functions is numerically impractical. We analyze here the third-order response function with Herman-Kluk dynamics with the two related goals of understanding the origins of the success of the approximation and developing a simplified representation that is more readily implemented numerically. The result is a semiclassical approximation to the nth-order spectroscopic response function in which an integration over n pairs of classical trajectories connected by distributions of discontinuous transitions is collapsed to a single phase-space integration, in which n continuous trajectories are linked by deterministic transitions. This significant simplification is shown to retain a full description of quantum effects.

Quantum cellular automata are arrays of identical finite-dimensional quantum systems, evolving in discrete-time steps by iterating a unitary operator G. Moreover the global evolution G is required to be causal (it propagates information at a bounded speed) and translation-invariant (it acts everywhere the same). Quantum cellular automata provide a model/architecture for distributed quantum computation. More generally, they encompass most of discrete-space discrete-time quantum theory. We give an overview of their theory, with particular focus on structure results; computability and universality results; and quantum simulation results.

The concept of Nonlinear Output Frequency Response Functions (NOFRFs) was introduced in [1] for the analysis of nonlinear systems in the frequency domain where a least-squares (LS) method was proposed for the evaluation of the NOFRFs using system input-output data. However, this leastsquares (LS) based approach may experience numerical errors due to matrix inversion and consequently cannot produce accurate NOFRFs sometimes. In order to mitigate this problem, in the present study, a modified LS method (M-LS) is proposed to make sure that the information matrix to be inverted for the LS solution is appropriately constructed so as to improve the condition number of the information matrix and reduce the numerical errors. Simulation results have demonstrated the effectiveness of the newly proposed method and indicated that the new method will enable a more accurate evaluation of the NOFRFs and facilitate the frequency analysis of nonlinear systems directly using system input-output data.