Quantum control based on machine learning in an open quantum system

Designing robust control schemes in n-level open quantum system is significant for quantum computation. Here, we investigate two quantum control strategies based on supervised machine learning to suppress the quantum noise in an open quantum system. One is controlling state distance and the other is governing the average of a Hermitian operator. In this process, the dynamics of the system is mapped to a neural network where the control fields correspond to the weights. Besides, the system is transformed into the coherence Bloch space without using superoperator thus the complications are reduced largely. As an example, the two control protocols are demonstrated in a two-level and four-level systems, respectively. By applying these examples, the results show that the state of the system transfers to the target state and the average of a Hermitian operator to its minimum value in a given time despite disturbed by various types of noise.     

Topological Phase Transition of Non-Hermitian Crosslinked Chain

The contents of topological classification of matter are enriched by non-Hermiticity, such as exceptional points, bulk-edge correspondence, and skin effects. Physically, gain and loss can be introduced by imaginary on-site potentials of lattice Hamiltonians, and the topological phase transition for a cross-linked chain in the presence of such non-Hermiticity is investigated. The topological phase diagram in terms of a winding number is obtained analytically with phase boundaries coinciding with the surfaces of exceptional points. The topologically original edge states with distribution mainly at the joints between domains of different phases are protected even for long chains. The non-Hermitian topological feature can also be reflected by vortex structures in the vector fields of complex eigenenergies, expected values of Pauli matrices, and trajectories of these quantities. This model may be implemented in coupled photonic crystals, fermions trapped in optical lattice, or non-Hermitian electrical-circuit lattices, and the edge states are immune to various kinds of disorders until topological phase transition occurs. This work gives insight into the influence of non-Hermiticity on topological phase of matter.     

Ground state cooling of magnomechanical resonator in PT-symmetric cavity magnomechanical system at room temperature

We propose to realize the ground state cooling of magnomechanical resonator in a parity–time (PT)-symmetric cavity magnomechanical system composed of a loss ferromagnetic sphere and a gain microwave cavity. In the scheme, the magnomechanical resonator can be cooled close to its ground state via the magnomechanical interaction, and it is found that the cooling effect in PT-symmetric system is much higher than that in non-PT-symmetric system. Resorting to the magnetic force noise spectrum, we investigate the final mean phonon number with experimentally feasible parameters and find surprisingly that the ground state cooling of magnomechanical resonator can be directly achieved at room temperature. Furthermore, we also illustrate that the ground state cooling can be flexibly controlled via the external magnetic field.     

Rhodium and iridium oxometallates- A new class of solid microporous materials

Organometallic Keggin ion complexes, exemplified by [(Ph₃P)₂Rh(CO)]₄SiW₁₂O₄₀ and [(Ph₃P)₂IrH₂]₃PW₁₂O₄₀ have been characterized by solid state NMR and X-ray absorption spectroscopy. They constitute a new class of chemically microporous solids and illustrate the use of large molecular metal oxide clusters to form extensible lattices in which coordinatively unsaturated organometallic cations may be stabilized and studied. In some cases, these cations are mobile and form bimetallic species. The reactions of those materials in olefin isomerization, hydroformylation, hydrogenation, dehydrogenation and C-H activation processes are described.     

Initial stages of oxidation of GaAs(111)2 × 2-Ga surfaces

The initial interaction of oxygen at room temperature with GaAs(111)2 × 2-Ga surfaces has been studied by quantitative Auger analysis and low-energy electron diffraction, under different electron irradiation and gas ionization conditions. Oxygen fills first the non-vacancy overlayer sites with a preferential bond to the Ga atoms. This adsorption phase is characterized by the absence of chemical shifts in the Ga Auger peaks that involve core levels. The oxidation stage begins with the occupation of the underlayer sites below the first Ga-As bilayer. For coverages lower than 2 monolayers oxygen adsorption and incorporation takes place without any loss of Ga or As atoms of the surface layers. Electron irradiation and gas ionization of the oxygen-covered surface increase the kinetics up to two orders of magnitude, but no changes in the adsorption sites and/or occupation sequence have been detected.     

Quantum adiabatic approximation to interacting boson-fermion systems

We present an adiabatic approximation method for the path integral of the Fermi field in the presence of a Bose field. The adiabatic phenomenon recently found by Berry and Simon is used for evaluating the Grassman path integral. Then we obtain the path integral of the effective action analogous to a magnetic field, and the quantization rule is derived by applying the semiclassical quantization method.     

论化学科学经验的传递机制——兼论化学课堂教学的最基本功能

从哲学本体论视角论述了化学科学经验传递机制,认为化学科学经验的课程化、教师化和学生化是化学科学经验传递的3个阶段,化学科学经验的学生化是化学课堂教学的最基本功能.     

多金属氧酸盐纳米材料的研究进展

多金属氧酸盐纳米材料是一类新型功能材料,由于其具有多酸的强氧化性和强酸性等优异性能,又具有纳米材料的功能特点,在催化合成和药物抗菌等方面具有重要意义。本文综述了近年来多酸纳米材料的合成与应用方面的进展,并对其化学合成的未来及应用进行了展望。