调制激光场中Rydberg原子的电磁感应透明

本文主要研究了调制探测激光场中铯Rydberg 原子阶梯型三能级系统的电磁感应透明(EIT) 效应. 铯原子基态6S_1/2, 第一激发态6P_3/2 和Rydberg 态形成阶梯型三能级系统, 探测光作用于6S_1/2 (F = 4)→6P_3/2(F' = 5) 的跃迁, 耦合光在Rydberg 跃迁线6P_3/2→49S_1/2 附近扫描, 形成Rydberg 原子EIT. 当对探测光频率施加一个几kHz 的调制时, 调制解调后的EIT 信号分裂为两个峰, 双峰间距与调制频率无关,而与调制幅度导致的失谐量大小(频率调制幅度) 成正比, 双峰间隔的一半等于探测光频率调制幅度的λ_p/λ_c = 1.67 倍. 实验结果与理论计算相一致. 本文的研究结果可应用于激光线型和频率抖动的实时监测.     

Quantum Zeno dynamics in atoms and cavities

Quantum Zeno Dynamics restricts the evolution of a system in a tailorable subspace of the Hilbert space by repeated measurements of a proper observable. This restricted dynamics can be counterintuitive and lead to the generation of interesting nonclassical states. We describe an experiment implementing the Zeno dynamics in an atomic Rydberg level manifold, and we propose an implementation in the cavity quantum electrodynamics context. Both systems open promising perspectives for quantum-enabled metrology and decoherence studies.     

Decay of metastable states in Nd II

The difficulty associated with an accurate determination of transition rates for forbidden lines in lowly ionized heavy elements is illustrated in the case of Nd II. We have investigated the radiative decay of the low-lying metastable levels in Nd⁺ including the two levels K_11/2 and I_13/2. In these two particular cases, using different theoretical approaches, we find that the decay is dominated by the M1 channels but that the E2 contributions are of the same order of magnitude. These levels have also been studied experimentally by lifetime measurements with the heavy ion storage ring CRYRING of Stockholm University. The difficulties encountered when performing such experiments are underlined and discussed.     

Generation of a four-qubit cluster state for atoms in a thermal cavity

We propose two schemes for generating a four-atom cluster state in a thermal cavity. With the assistant of a strong classical field the photon-number-dependent parts in the effective Hamiltonian are canceled. Thus the schemes are insensitive to the thermal field. The schemes can also be used to generate the cluster state for the trapped ions in thermal motion.     

The Girardeau's fermion-boson procedure in the light of the composite-boson many-body theory

We reconsider the procedure developed for atoms a few decades ago by Girardeau, in the light of the composite-boson many-body theory we recently proposed. The Girardeau's procedure makes use of a so called “unitary Fock-Tani operator” which in an exact way transforms one composite bound atom into one bosonic “ideal” atom. When used to transform the Hamiltonian of interacting atoms, this operator generates an extremely complex set of effective scatterings between ideal bosonic atoms and free fermions which makes the transformed Hamiltonian impossible to write explicitly, in this way forcing to some truncation. The scatterings restricted to the ideal-atom subspace are shown to read rather simply in terms of the two elementary scatterings of the composite-boson many-body theory, namely, the energy-like direct interaction scatterings — which describe fermion interactions without fermion exchange — and the dimensionless Pauli scatterings — which describe fermion exchanges without fermion interaction. We here show that, due to a fundamental difference in the scalar products of elementary and composite bosons, the Hamiltonian expectation value for N ground state atoms obtained by staying in the ideal-atom subspace and working with boson operators only, differ from the exact ones even for N = 2 and a mapping to the ideal-atom subspace performed, as advocated, from the fully antisymmetrical atomic state, i.e., the state which obeys the so-called “subsidiary condition”. This shows that, within this Girardeau's procedure too, we cannot completely forget the underlying fermionic components of the particles if we want to correctly describe their interactions.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

Spontaneous Ga incorporation in ZnO nanowires epitaxially grown on GaN substrate

Surface‐diffusion‐induced spontaneous Ga incorporation process is demonstrated in ZnO nanowires grown on GaN substrate. Crucially, contrasting distributions of Ga atoms in axial and radial directions are experimentally observed. Ga atoms uniformly distribute along the ～10 μm long ZnO nanowire and show a rapidly gradient distribution in the radial direction, which is attributed substantially to the difference between surface and volume diffusion. The understanding on the incorporation process can potentially modulate doping and properties in semiconductor nanomaterials.

     

Investigation of a Photochromic Diarylethene with Electron-acceptor Attached

In this contribution, an electron acceptor attached diarylethene derivative was synthesized and fully characterized. The photochromic behavior was investigated in THF. Under exposure of UV and visible light cycles, the solution color can be switched between colorless and yellow smoothly. Fatigue resistance measurements could be repeated 50 times with an acceptable degradation. Due to the electron acceptor attached to the framework of diarylethene, the photo- and thermal-stability were enhanced both. A full-photo mode switch can be established based on the well-defined states by external excitation. The molecular structures of ring-open and ring-closed form were optimized by Dmol³. The distance between photocyclizing atoms in aptiparallel conformation meets the requirement for photochromic reaction. And the calculated absorption wavelengths were also in agreement with the experimental values.     

On the strength of hydrogen bonding within water clusters on the coordination limit

Hydrogen bonds (HB) are arguably the most important noncovalent interactions in chemistry. We study herein how differences in connectivity alter the strength of HBs within water clusters of different sizes. We used for this purpose the interacting quantum atoms energy partition, which allows for the quantification of HB formation energies within a molecular cluster. We could expand our previously reported hierarchy of HB strength in these systems (Phys. Chem. Chem. Phys., 2016, 18 , 19557) to include tetracoordinated monomers. Surprisingly, the HBs between tetracoordinated water molecules are not the strongest HBs despite the widespread occurrence of these motifs (e.g., in ice I_h). The strongest HBs within H₂O clusters involve tricoordinated monomers. Nonetheless, HB tetracoordination is preferred in large water clusters because (a) it reduces HB anticooperativity associated with double HB donors and acceptors and (b) it results in a larger number of favorable interactions in the system. Finally, we also discuss (a) the importance of exchange-correlation to discriminate among the different examined types of HBs within H₂O clusters, (b) the use of the above-mentioned scale to quickly assess the relative stability of different isomers of a given water cluster, and (c) how the findings of this research can be exploited to indagate about the formation of polymorphs in crystallography. Overall, we expect that this investigation will provide valuable insights into the subtle interplay of tri- and tetracoordination in HB donors and acceptors as well as the ensuing interaction energies within H₂O clusters.     

化学学科核心素养指引下的“配合物”教学探讨

指出了高中阶段“配合物”教学中存在的问题,并从“应用杂化轨道理论解决配合物中心部分的空轨道问题”“尝试判断配位原子”“用平衡思想理解配合物的内界组成”等3个方面阐述了如何在化学学科核心素养的指导下引导学生更好地进行配合物知识的学习。