Árpád I. Csurgay

On circuit models for quantum‐classical networks

Physics is not scale invariant, and today the scale of atoms and molecules challenges designers of machines in which quantum effects have dominant sway. What role could circuit theory play in designing machines described by quantum-classical models? Classical equivalent circuits do exist for systems composed of metal contacted and wired devices, such as resonant tunneling diodes, single electron transistors, metal–insulator–metal diodes, etc. circuits, but not for quantum-entangled networks, such as multi-quantum-state atoms. n n n nIf devices were not contacted and wired by macroscopic metals, i.e. devices were classically field coupled, then generalized circuit models can be introduced. Case studies have been presented on the role of circuit models in quantum-classical systems. However, there are no ideal circuit elements capable of capturing the port properties of quantum-mechanical and/or quantum-optical subsystems and their coupling to classical waveguides or cavities. Copyright

Threshold Gate-Based Circuits From Nanomagnetic Logic

This paper demonstrates the design of nanomagnetic logic (NML) gates with multiple weighted inputs, which are magnetic equivalents of threshold logic gates (TLGs). We use micromagnetic simulations to show that NML TLGs can be constructed with minimum overhead compared to standard NML gates, and they significantly reduce device footprint and interconnection complexity of magnetic logic circuits. As an example, we design a full adder circuit using said TLGs and compare its performance to majority-gate-based NML.

On circuit models for quantum-classical networks: Research Articles

The problems associated with combining multiple GSM carriers and WCDMA signals onto a single antenna are developed leading to a unique solution. This solution is based upon the concept of cascading directional filters to meet the electrical requirements, which may readily be tuned electrically leading to remote-tuned products capable of injecting one or more WCDMA channels into the same communication band as several GSM carriers. n nA particular solution is presented, which exhibits both optimum amplitude and group delay characteristics for the WCDMA signal. Closed-form expressions are given for the network functions including the amplitude and group delay characteristics. By developing techniques similar to those used in Rhodes (Theory of Electrical Filters. Wiley: New York, 1976), explicit formulas for element values in the general 2nth degree network are given and proved. n nA practical operating unit for the US cellular band has been designed and constructed. Measured per- formance is given and shows excellent agreement with theory. Copyright

Nanoscale spectrum analyzer based on spin-wave interference

We present the design of a spin-wave-based microwave signal processing device. The microwave signal is first converted into spin-wave excitations, which propagate in a patterned magnetic thin-film. An interference pattern is formed in the film and its intensity distribution at appropriate read-out locations gives the spectral decomposition of the signal. We use analytic calculations and micromagnetic simulations to verify and to analyze the operation of the device. The results suggest that all performance figures of this magnetoelectric device at room temperature (speed, area, power consumption) may be significantly better than what is achievable in a purely electrical system. We envision that a new class of low-power, high-speed, special-purpose signal processors can be realized by spin-waves.

Single electron transistor based chua type chaotic circuit: A SPICE assisted proof

This paper describes a scheme to design Chua type double scroll circuit using single electron transistors. This is a first attempt to show that single electron transistors can be used to design Chua type double scroll circuits. A SPICE assisted proof is presented as partial results of ongoing work to show the possibility of such chaotic circuit at nanotechnology.

Circuit models for arrays of nanoelectronic resonators—Appearances of discrete breathers

In this paper, equivalent-circuit representations are presented for nonlinear arrays of weakly coupled molecular oscillators demonstrating intrinsic localized oscillating modes, also called ‘discrete breathers’. Typical examples are arrays or strings of diatomic molecules coupled, e.g. with weak hydrogen bonds, or arrays of field-coupled nanodevice resonators. Circuits demonstrating discrete breathing are presented. Copyright

Toward engineering design of quantum circuits.

Summary nA new engineering discipline called ‘quantum technology’ is emerging. Nanotechnology and cryotechnology enable engineers to develop devices and integrated circuits in which quantum phenomena have dominant sway. Macroscopic finite-state ‘artificial atoms’ are realized exploiting superconductive Josephson effect, and these ‘atoms’ exchange microwave photons in superconductive microwave circuits. The achievements of cavity quantum electrodynamics in quantum optics are mimicked in the microwave frequency range. The new technology is dubbed circuit quantum electrodynamics. This paper tries to call the attention of engineers majoring in circuit theory and design on the challenges they face in designing quantum circuits. Modeling and simulation of quantum circuit components are reviewed. Approximate closed quantum system models as well as more accurate open system models are introduced in the case of single quantum devices and composite quantum systems. The effects of amplitude damping and phase damping are illustrated by simulation. The role of classical resistors in quantum circuits is investigated. Special attention is given to the almost standardized technology developed for superconductive microwave quantum circuits. Open problems are identified that circuit designers face in developing computer-aided-design tools for quantum circuits. Copyright

Simulation-based investigation of the three-dimensional distribution of fluorescence and photobleaching in multi-photon excited samples

We present a numerical study on the spatial distribution of fluorescence and photobleaching occurring in samples subject to multi-photon excitation. We developed a simulation model and implemented a simulator program. Its quantitative predictions can help to find the optimal operating parameters (such as laser power, pulse length, pulse repetition rate) of the two-photon microscope to reach higher image quality, to reduce undesired photobleaching, and to pave the way for optimized photoswitching-based super-resolution imaging. Conversely, the simulator might also be useful when photodynamic parameters are searched for. Furthermore, such simulations can promote the evaluation of the results of other fluorescence-based techniques [e.g. fluorescence recovery after photobleaching (FRAP) measurements]. The photodynamic model of the fluorophore contains a ground state, an excited state, a triplet state, and several photobleached states; the state transitions are characterized by absorption cross sections and lifetimes. The sample is modeled as a fluorophore solution divided into cubic cells among which diffusion takes place. The illumination is simulated as a focused laser pulse train described by a pulsed Gaussian beam. As a demonstration of the capabilities of the simulator, an example is presented that reveals the spatial distribution of photon emission in the sample investigated by a two-photon microscope in the case of different laser and photobleaching parameters, assuming one-photon absorption induced photobleaching. The simulation demonstrates quantitatively how photobleaching affects the spatial distribution of fluorescence and the resolution of the microscope.

Impact of undamped and damped intramolecular vibrations on the efficiency of photosynthetic exciton energy transfer

In recent years, the role of molecular vibrations in exciton energy transfer taking place during the first stage of photosynthesis attracted increasing interest. Here, we present a model formulated as a Lindblad-type master equation that enables us to investigate the impact of undamped and especially damped intramolecular vibrational modes on the exciton energy transfer, particularly its efficiency. Our simulations confirm the already reported effects that the presence of an intramolecular vibrational mode can compensate the energy detuning of electronic states, thus promoting the energy transfer; and, moreover, that the damping of such a vibrational mode (in other words, vibrational relaxation) can further enhance the efficiency of the process by generating directionality in the energy flow. As a novel result, we show that this enhancement surpasses the one caused by pure dephasing, and we present its dependence on various system parameters (time constants of the environment-induced relaxation and excitation processes, detuning of the electronic energy levels, frequency of the intramolecular vibrational modes, Huang–Rhys factors, temperature) in dimer model systems. We demonstrate that vibrational-relaxation-enhanced exciton energy transfer (VREEET) is robust against the change of these characteristics of the system and occurs in wide ranges of the investigated parameters. With simulations performed on a heptamer model inspired by the Fenna–Matthews–Olson (FMO) complex, we show that this mechanism can be even more significant in larger systems at T = 300 K. Our results suggests that VREEET might be prevalent in light-harvesting complexes.In recent years, the role of molecular vibrations in exciton energy transfer taking place during the first stage of photosynthesis attracted increasing interest. Here, we present a model formulated as a Lindblad-type master equation that enables us to investigate the impact of undamped and especially damped intramolecular vibrational modes on the exciton energy transfer, particularly its efficiency. Our simulations confirm the already reported effects that the presence of an intramolecular vibrational mode can compensate the energy detuning of electronic states, thus promoting the energy transfer; and, moreover, that the damping of such a vibrational mode (in other words, vibrational relaxation) can further enhance the efficiency of the process by generating directionality in the energy flow. As a novel result, we show that this enhancement surpasses the one caused by pure dephasing, and we present its dependence on various system parameters (time constants of the environment-induced relaxation and excita...

Fluorescence in two-photon-excited diffusible samples exposed to photobleaching: a simulation-based study

Abstract. We created a simulation model to investigate the characteristics of fluorescence in two-photon-excited samples. In the model, the sample is a diffusible solution of fluorophore molecules, which is divided into cubic cells and illuminated by a train of focused laser pulses described as a Gaussian beam. Simulating the state transitions according to a multilevel photodynamic model (also including photobleaching and intersystem crossing), the simulator provides the expected number and the spatial distribution of emitted photons over time. Our simulations demonstrated how the illumination laser power, diffusion, and the photodynamic parameters of the fluorophore affect fluorescence. We revealed the unusual fluorescent profile that evolves as photobleaching progresses: the most photons are not emitted from the focus (where a “dark hole” appears) but from an ellipsoid around the focus. The model could be adapted to several fluorescent techniques (such as two-photon microscopy and fluorescence recovery after photobleaching). Furthermore, it might help to optimize the operating parameters of the measurement devices (e.g., in order to reach higher image quality and lower photobleaching).