Indirect optimal control of a double quantum dot

An indirect optimization method for the dynamic control of non-Markovian open quantum systems is presented. It is demonstrated at the example of a spin-boson model for an electron in a double dot which couples to a bath of phonons. This study reveals strategies for controlling the effective system-bath coupling which become available when the system is addressed in its quantum regime. We give examples for population transfer, trapping and quantum operations.     

Scattering resonances in 1D coherent transport through a correlated quantum dot: An application of the few-particle quantum transmitting boundary method

We present a method for the calculation of the scattering states of a N+1th-particle coherently interacting with N correlated particles confined in a nanostructure and placed within an open domain. The method is based on a generalization of the quantum transmitting boundary method [C. Lent and D. Kirkner, J. App. Phys. 67, 6353 (1990)]. The antisymmetry conditions of the N+1-identical particles current-carrying state results from a proper choice of the boundary conditions. As an example which is relevant to coherent electronics, we apply the method to compute the exact transmission functions and phases of an electron crossing a 1D quantum dot with zero, one or two bound electrons.     

3D simulation of a silicon quantum dot in a magnetic field based on current spin density functional theory

We have developed a code for the simulation of the electrical and magnetic properties of silicon quantum dots in the framework of the TCAD Package NANOTCAD-ViDES. We adopt current spin density functional theory with a local density approximation and with the effective mass approximation. We show that silicon quantum dots exhibit large variations of the total spin as the number of electrons in the dot and the applied magnetic field are varied. Such properties are mainly due to the silicon band structure, and make silicon quantum dots interesting systems for spintronic and quantum computing experiments.     

Shot noise in transport through quantum dots: Clean versus disordered samples

We investigate the role of disorder and diffractive scattering in the shot noise power of quantum transport through a two-dimensional quantum dot. By tuning the strength of the disorder potential and the openings of the dot, we numerically explore the influence of quantum scattering mechanisms on the current shot noise. For small cavity openings we find the shot noise for disordered samples to be of almost equal magnitude as for clean samples where transport is ballistic. We explain this finding by diffractive scattering at the cavity openings which act as strong noise sources. Estimates for the shot noise induced by both the disorder potential and the diffractive openings are presented that agree with the numerical data.     

Architecture for an external input into a molecular QCA circuit

A simple architecture for data input into a molecular quantum-dot cellular automata (QCA) circuit from an external CMOS circuit is proposed. A “T”-shaped interconnect, utilizing fixed-polarization cells to provide the desired polarization, is controlled via external electrodes connected to a standard CMOS input driver. The applied input signal is used to gate either the propagation of a fixed polarization, P=+1, or that of the complementary fixed polarization, P=−1, into the QCA circuit. The architecture utilizes the field-driven clocking scheme proposed in recent literature to achieve transduction between applied input voltage and a molecular configuration. The system is modelled using the coherence vector formalism with a three-state basis and simulated using the QCADesigner simulation tool.     

Performance of a novel dot matrix fuel cell using an inorganic micro‐proton conductor

The power generation properties of a novel dot matrix fuel cell using an inorganic micro‐proton conductor were evaluated in dry gas mixtures of hydrogen and oxygen during room‐temperature operation. The single dot matrix fuel cell was composed of aggregates of micro‐electrolyte dots filling pores arranged in a matrix form on a Teflon or polyimide substrate with Pt/C and Pt catalytic electrodes. Micro‐electrolyte dots were prepared by the sol–gel method using titanium phosphorus oxides as the proton conductive hybrid materials. The open‐circuit voltage of the single cell became higher when using a small dot diameter and achieved a maximum of 500 mV with an electrolyte dot density of 17 dots/cm² in the dry gas mixtures during room‐temperature operation. This value corresponds to about one‐half of the theoretical electromotive force. Moreover, the current density of the single cell increased with the dot diameter such that it grew to 8 mA/cm² at a dot diameter of 500 µm. As a result, dot matrix fuel cells connected in series and parallel were found to achieve the cell performance of high‐energy density such as used by high‐energy microchips. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A systematic approach to designing a wide‐current range,MOS capacitor‐based switched‐capacitor DC‐DC converter with an augmenting LDO

Switched‐capacitor DC‐DC converters (SC DC‐DC) are analyzed for loss sources, voltage regulation integrity, start‐up latency, and ripple size, while the trade‐offs between these metrics are derived. These analyses are used to design a SC DC‐DC that achieves high efficiency in a wide load current range. Four‐way interleaving was employed to reduce the output ripple and efficiency loss due to this ripple. The design can be reconfigured to achieve gains of 1/3 and 2/5 for inputs ranging between 1.4 and 3.6 V to generate output voltage range of 0.4 to 1.27 V and can supply peak load current of 22 mA. It uses thin‐oxide MOS capacitors for their high density and achieves 75.4% peak efficiency with an input frequency of 100 MHz and a load capacitor of 10 nF. An augmenting LDO that only regulates during sudden load transients helps the converter respond fast to these transients. The chip was implemented using a 65‐nm standard CMOS process.