Unusual Compression Behavior of Columbite TiO2 via First-Principles Calculations

The physical mechanisms behind the reduction of the bulk modulus of a high-pressure cubic TiO2 phase are confirmed by first-principles calculations. An unusual and abrupt change occurs in the dependence of energy on pressure at 43 GPa, indicating a pressure-induced phase transition from columbite TiO2 to a newly-identified modified fluorite TiO2 with a Pca21 symmetry. Oxygen atom displacement in Pca21 TiO2 unexpectedly reduces the bulk modulus by 34% relative to fluorite TiO2. This discovering provides a direct evidence for understanding the compressive properties of such groups of homologous materialsComment: [email protected] or [email protected]

Ab initio study of the formation of transparent carbon under pressure

A body-centered tetragonal carbon (bct-Carbon) allotrope has been predicted to be a transparent carbon polymorph obtained under pressure. The structural transition pathways from graphite to diamond, M-Carbon, and bct-Carbon are simulated and the lowest activation barrier is found for the graphite-bct transition. Furthermore, bct-Carbon has higher shear strength than diamond due to its perpendicular graphene-like structure. Our results provide a possible explanation for the formation of a transparent carbon allotrope via the cold compression of graphite. We also verify that this allotrope is hard enough to crack diamond.Comment: [email protected] or [email protected]

A low-crosstalk double-side addressing system using acousto-optic deflectors for atomic ion qubits

The ability to individually and agilely manipulate qubits is crucial for the scalable trapped-ion quantum information processing. A plethora of challenging proposals have been demonstrated with the utilization of optical addressing systems, in which single ions is addressed exclusively by individual laser beam. However, crosstalk error in optical addressing systems limits the gate fidelity, becoming an obstacle to quantum computing, especially quantum error correction. In this work, we demonstrate a low-crosstalk double-side addressing system based on a pair of acousto-optic deflectors (AODs). The AODs addressing method can flexibly and parallelly address arbitrary ions between which the distance is variable in a chain. We employ two 0.4~NA objective lenses in both arms of the Raman laser and obtain a beam waist of 0.95~$\mu\mathrm{m}$, resulting in a Rabi rate crosstalk as low as $6.32\times10^{-4}$ when the neighboring ion separation is about 5.5~$\mu\mathrm{m}$. This agile and low-crosstalk double-side addressing system is promising for higher-fidelity gates and the practical application of the quantum error correction

LPV robust servo control of aircraft active side-sticks

Purpose This paper aims to focus on the variable stick force-displacement (SFD) gradience in the active side stick (ASS) servo system for the civil aircraft. Design/methodology/approach The problem of variable SFD gradience was introduced first, followed by the analysis of its impact on the ASS servo system. To solve this problem, a linear-parameter-varying (LPV) control approach was suggested to process the variable gradience of the SFD. A H∞ robust control method was proposed to deal with the external disturbance. Findings To validate the algorithm performance, a linear time-variant system was calculated to be used to worst cases and the SFD gradience was set to linear and non-linear variation to test the algorithm, and some typical examples of pitch angle and side-slip angle tracking control for a large civil aircraft were also used to verify the algorithm. The results showed that the LPV control method had less settling time and less steady tracking errors than H∞ control, even in the variable SFD case. Practical implications This paper presented an ASS servo system using the LPV control method to solve the problem caused by the variable SFD gradience. The motor torque command was calculated by pressure and position feedback without additional hardware support. It was more useful for the electronic hydraulic servo actuator. Originality/value This was the research paper that analyzed the impact of the variable SFD gradience in the ASS servo system and presented an LPV control method to solve it. It was applicable for the SFD gradience changing in the linear and non-linear cases