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68 DESIGN007 MAGAZINE I AUGUST 2018 Gbps NRZ signal. However, it degraded the accuracy of the model with 56 Gbps PAM-4, and it looks like the signal energy above 28 GHz is more important to account for in this case, in order to have the analysis that corre- lates with the measurements. The absence of the correlation would probably not prevent the link operation in this case; the slight eye degradation will be handled by the adaptive Rx/Tx. This may be different for links at the border of the Tx/Rx compliance margins. The bottom line is that the modeling of PAM-4 links with double data rates is more challenging than for the NRZ. The correla- tion bandwidth of the models should be extended for PAM-4. This means that the design process must include manufacturing adjustments and material model identifica- tion, and, most importantly, the interconnect analysis software should be validated up to 40-50 GHz for 56 Gbps PAM-4 links. It may sound ridiculous, but most of the interconnect analysis tools are not vali- dated and, moreover, cannot be validated. The key in the validation is to make the minimal number of initial steps (geometry adjustments and material model identifica- tion) and apply the tool to typical intercon- nect structures without further adjustments. This is how we introduced the CMP-28 board with Wild River Technology about five years ago and demonstrated on EvR-1 board with Marko Marin at DesignCon 2018. This is all about building the process and validating the tools. Do not trust the tool vendors just because you paid a lot for the tool or it's described as "3D electromag- netic," or the marketing manager says that the tool is accurate and even "intelligent" and validated, even if he shows you a couple of cases. Trust, but validate everything! DESIGN007 Yuriy Shlepnev is founder and president of Simberian Inc. Novel Approach to Coherent Control of a Three-Level Quantum System For the first time, researchers were able to study quan- tum interference in a three-level quantum system and thereby control the behavior of individual electron spins. To this end, they used a novel nanostructure, in which a quantum system is integrated into a nanoscale mechani- cal oscillator in form of a diamond cantilever. Nature Phys- ics has published the study that was conducted at the University of Basel and the Swiss Nanoscience Institute. The electronic spin is a fundamental quantum mechani- cal property intrinsic to every electron. In the quantum world, the electronic spin describes the direction of rota- tion of the electron around its axis which can normally occupy two so-called eigenstates commonly denoted as "up" and "down." The quantum properties of such spins offer interesting perspectives for future technologies, for example in the form of extremely precise quantum sensors. Researchers led by Professor Patrick Maletinsky and PhD candidate Arne Barfuss from the Swiss Nanoscience Institute at the University of Basel report in Nature Phys - ics a new method to control the spins' quantum behavior through a mechanical system. For their experimental study, they combined such a quantum system with a mechanical oscillator. More spe - cifically, the researchers employed electrons trapped in so-called nitrogen-vacancy centers and embedded these spins in single-crystalline mechanical resonators made from diamond. In particular, the oscillator allowed them to address all three possible transitions in the spin and to study how the resulting excitation pathways interfere with each other. Source: University of Basel

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