量子机器学习简介及其在特定场景中的应用

近些年来,机器学习对各行各业产生了深远影响,特别是把量子计算的特性与机器学习相结合而形成的量子机器学习,实现了对传统算法的加速.目前,量子机器学习在物理、化学、金融和生物医药等领域的应用引起了人们的极大关注.本文首先介绍了量子机器学习的基本概念和目前的前沿进展.其次以氟化氢分子为例子,利用量子机器学习计算了该分子系统的基态能量.

Entanglement Evolution of Two-Coupled Spins in a Time-Dependent Rotating Magnetic Field

We study the dynamics evolution of a two-qubit Heisenberg XXX spin chain under a time-dependentrotating magnetic field.Based on the algebraic structure of the non-autonomous system,the exact solution of theSchrdinger equation is obtained by using the method of algebraic dynamics.Based on the time-dependent analyticalsolution,we further study the entanglement evolution between the two coupled spins for different initial states,and findthat the entanglement is determined by the coefficients of the initial state and the coupling constant J of the system.

Strain Distributions in Non-Polar a-Plane In_(x)Ga_(1−x)N Epitaxial Layers on r-Plane Sapphire Extracted from X-Ray Diffraction

By using x-ray diffraction analysis,we investigate the major structural parameters such as strain state and crystal quality of non-polar a-plane In_(x)𝑦Ga_(1−x)𝑦N thin films grown on r-sapphire substrates by metalorganic chemical vapour deposition.The results of the inplane grazing incidence diffraction technique are analyzed and compared with a complementary out-of-plane high resolution x-ray diffraction technique.When the indium composition is low,the a-plane In_(x)𝑦Ga_(1−x)𝑦N layer is tensile strain in the growth direction(𝑏a-axis)and compressive strain in the two in-plane directions(𝑛a-axis and𝑑a-axis).The strain status becomes contrary when the indium composition is high.The stress in the𝑛a-axis direction𝜏σyy is larger than that in the a-axis directionσzz.Furthermore,strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the In_(x)Ga_(1−z)N film.

The Growth of Semi-Polar ZnO (1011) on Si (111) Substrates Using a Methanol Oxidant by Metalorganic Chemical Vapor Deposition

Semi-polar ZnO (1011) epitaxial films are demonstrated using a methanol oxidant by metalorganic chemical vapor deposition on Si (111) substrates at 500℃.X-ray (O) scanning indicates that there are six kinds of in-plane domain growths,with the ZnO [1012] parallel to the Si (11(2)〉 direction families.The crystallographic orientation of ZnO is supposed to be caused by surface passivation.The methanol,as a polar molecule,may be adsorbed on the Si (111) surface to form a passivation layer,which inhibits the (0001) ZnO plane deposition on the substrate surface,and as a result the ZnO (1011) plane becomes preferred.The optical properties,examined by a roomtemperature photoluminescence spectrum,exhibit a strong near-band-edge emission peak at 379nm,indicating that the (1011) ZnO film has good crystal quality.These results are significant for research into and for the applications of semi-polar ZnO films.

Morphological Evolution of a-GaN on r-Sapphire by Metalorganic Chemical Vapor Deposition

The morphological evolution of a-GaN deposited by metalorganic chemical vapor deposition (MOCVD) on rsapphire is studied.The influences of Ⅴ/Ⅲ ratio and growth temperature on surface morphology are investigated.Ⅴ-pits and stripes are observed on the surface of a-GaN grown at 1050 ℃ and 1100℃,respectively.The overall orientation and geometry of Ⅴ-pits are uniform and independent on the Ⅴ/Ⅲ molar ratio in the samples grown at 1050 ℃,while in the samples grown at 1100 ℃,the areas of stripes decrease with the adding of Ⅴ/Ⅲ ratio.We deduce the origin of Ⅴ-pits and stripes by annealing the buffer layers at different temperatures.Because of the existence of inclined (10(-1)1) facets,Ⅴ-pits are formed at 1050℃.The (10(-1)1) plane is an N terminated surface,which is metastable at higher temperature,so stripes instead of V-pits are observed at 1100℃.Raman spectra suggest that the growth temperature of the first layer in the two-step process greatly affects the strain of the films.Hence,to improve the growth temperature of the first layer in the two-step method may be an effective way to obtain high quality a-GaN film on r-sapphire.

Growth and Characterization of an a-Plane In_(x)Ga_(1−x)N on a r-Plane Sapphire

The non-polar a-plane(1120)In_(x)Ga_(1−x)N alloys with different indium compositions(0.074≤x≤0.555)were grown on r-plane(1012)sapphire substrates by metalorganic chemical vapor deposition,and the indium compositions x are estimated from x-ray diffraction measurements.The in-plane orientation of the In_(x)Ga_(1−x)N with respect to the r-plane substrate is confirmed to be[1100]sapphire||[1120]In_(x)Ga_(1−x)N and[1101]sapphire||[0001]In_(x)Ga_(1−x)N.The effects of substrate temperature,reactor pressure and trimethylindium input flow on the indium incorporation and growth rate are investigated.The morphology of the a-plane In_(x)Ga_(1−x)N is found to be significantly improved with the decreasing indium composition x and growth rate.Moreover,the in-plane anisotropic structural characteristics are revealed by high resolution x-ray diffraction employing azimuthal dependence,and the degree of anisotropy decreases with the increase of indium composition.