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Ehrenfest Time at the Transition from Integrable Motion to Chaotic Motion

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Chinese Physics Letters 2021年第3期38卷 29-32页

作者： Chuan Zhao Biao Wu International center for quantum Materials School of PhysicsPeking UniversityBeijing 100871China Wilczek quantum center School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Collaborative Innovation center of quantum Matter Beijing 100871China

Ehrenfest time depends differently on the Planck constant in integrable motion and chaotic motion. We study how its dependence on the Planck constant changes when there is a continuous transition from regular motion to chaotic motion. We find that the dependence is a weighted compromise between its two distinct dependences in regular and chaotic motions. The study is carried out with the system of periodically driven anharmonic oscillator. As the system is quite typical, the result may apply generally.

关键词： motion. chaotic system

Interconversion of photon-phonon in a silica optomechanical microresonator

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Science China(Physics,Mechanics & Astronomy) 2015年第5期58卷 64-69页

作者： DONG ChunHua SHEN Zhen ZOU ChangLing GUO GuangCan Key Laboratory of quantum Information Chinese Academy of Sciences University of Science and Technology of China Synergetic Innovation center of quantum Information and quantum Physics University of Science and Technology of China

In an optomechanical resonator, the optical and mechanical excitations can be coherently converted, which induces a transparency window for a weak probe laser beam. Here, we report an experimental study of transient optomechanically induced transparency(OMIT) using the silica microsphere with the breathing modes. The transient OMIT behavior obtained are in good agreement with theoretical calculations. In addition, the coherent interconversion between optical and mechanical excitations that can be used for light storage and readout has also been studied here. Our experimental results indicate that the light storage is closely related to the process of OMIT, and the photon-phonon conversion can be further applied to optical wavelength or optical mode conversion.

关键词： cavity optomechanics optomechanically induced transparency microsphere

Hybrid opto-mechanical systems with nitrogen-vacancy centers

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Science China(Physics,Mechanics & Astronomy) 2015年第5期58卷 29-40页

作者： YIN ZhangQi ZHAO Nan LI TongCang center for quantum Information Institute for Interdisciplinary Information Sciences Tsinghua University Beijing Computational Science Research center Synergetic Innovation center of quantum Information and quantum Physics University of Science and Technology of China Department of Physics and Astronomy and School of Electrical and Computer Engineering Purdue University Birck Nanotechnology center Purdue University

In this review, we briefly review recent works on hybrid （nano） and diamond nitrogen-vacancy （NV） centers. We also review opto-mechanical systems that contain both mechanical oscillators two different types of mechanical oscillators. The first one is a clamped mechanical oscillator, such as a cantilever, with a fixed frequency. The second one is an optically trapped nano-diamond with a built-in nitrogen-vacancy center. By coupling mechanical resonators with electron spins, we can use the spins to control the motion of mechanical oscillators. For the first setup, we discuss two different coupling mechanisms, which are magnetic coupling and strain induced coupling. We summarize their applications such as cooling the mechanical oscillator, generating entanglements between NV centers, squeezing spin ensembles etc. For the second setup, we discuss how to generate quantum superposition states with magnetic coupling, and realize matter wave interferometer. We will also review its applications as ultra-sensitive mass spectrometer. Finally, we discuss new coupling mechanisms and applications of the field.

关键词： opto-mechanics nitrogen-vacancy center hybrid system

Passive decoy-state quantum key distribution using weak coherent pulses with modulator attenuation

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Chinese Physics B 2015年第11期24卷 118-124页

作者：李源鲍皖苏李宏伟周淳汪洋 Zhengzhou Information Science and Technology Institute Synergetic Innovation center of quantum Information and quantum Physics University of Science and Technology of China

Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on the passive decoy-state method is considered. We introduce and analyze the unbalanced Mach-Zehnder interferometer, briefly, and combining with the virtual source and imaginary unitary transformation, we characterize the passive decoy-state method using a weak coherent photon source with modulator attenuation. According to the attenuation parameter 6, the pass efficiencies are given. Then, the key generation rate can be acquired. From numerical simulations, it can be seen that modulator attenuation has a non- negligible influence on the performance of passive-state QKD protocol. Based on the research, the analysis method of virtual source and imaginary unitary transformation are preferred in analyzing passive decoy state protocol, and the passive decoy-state method is better than the active one and is close to the active vacuum ＋ weak decoy state under the condition of having the same modulator attenuation.

关键词： quantum key distribution passive decoy state modulator attenuation weak coherent pulses

quantum algorithm for a set of quantum 2SAT problems

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Chinese Physics B 2021年第2期30卷 59-63页

作者： Yanglin Hu Zhelun Zhang Biao Wu International center for quantum Materials School of PhysicsPeking UniversityBeijing 100871China Wilczek quantum center School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Collaborative Innovation center of quantum Matter Beijing 100871China

We present a quantum adiabatic algorithm for a set of quantum 2-satisfiability(Q2SAT)problem,which is a generalization of 2-satisfiability(2SAT)*** a Q2SAT problem,we construct the Hamiltonian which is similar to that of a Heisenberg *** the solutions of the given Q2SAT problem span the subspace of the degenerate ground *** Hamiltonian is adiabatically evolved so that the system stays in the degenerate *** numerical results suggest that the time complexity of our algorithm is O(n^(3.9))for yielding non-trivial solutions for problems with the number of clauses m=dn(n-1)/2(d■0.1).We discuss the advantages of our algorithm over the known quantum and classical algorithms.

关键词： adiabatic quantum computation quantum Hamiltonian algorithm quantum 2SAT problem

Optimized quantum random-walk search algorithm for multi-solution search

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Chinese Physics B 2015年第11期24卷 133-139页

作者：张宇超鲍皖苏汪翔付向群 Zhengzhou Information Science and Technology Institute Synergetic Innovation center of quantum Information and quantum Physics University of Science and Technology of China

This study investigates the multi-solution search of the optimized quantum random-walk search algorithm on the hypercube. Through generalizing the abstract search algorithm which is a general tool for analyzing the search on the graph to the multi-solution case, it can be applied to analyze the multi-solution case of quantum random-walk search on the graph directly. Thus, the computational complexity of the optimized quantum random-walk search algorithm for the multi-solution search is obtained. Through numerical simulations and analysis, we obtain a critical value of the proportion of solutions q. For a given q, we derive the relationship between the success rate of the algorithm and the number of iterations when q is no longer than the critical value.

关键词： quantum search algorithm quantum random walk multi-solution abstract search algorithm

Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy

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Chinese Physics B 2014年第6期23卷 181-187页

作者：刘源张凌峰宁传刚 Department of Physics State Key Laboratory of Low-Dimensional Quantum Physics Tsinghua University Collaborative Innovation center of quantum Matter

Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow＇s work titled ＂Is it time to retire the hybrid atomic orbital？＂ [J. Chem. Educ. 88, 860 （2011）]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H20 are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental （e, 2e） results.

关键词： electron momentum spectroscopy delocalized molecular orbital localized molecular orbital

The modelling of quantum control systems

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Science Bulletin 2015年第17期60卷 1493-1508页

作者： Wenbin Dong Rebing Wu Xiaohu Yuan Chunwen Li Tzyh-Jong Tarn Department of Automation Tsinghua University center for quantum Information Science and Technology TNList Electrical and systems Engineering Department Washington University in St. Louis

High-performance control of quantum dynamics is key to the development of quantum *** quantum-state engineering to quantum metrology,theory and practice of quantum control enable robust and cheaper technologies for future industrial *** from fundamental matter–field interactions, we overview various approaches to modelling quantum control systems, in which control can be implemented by either changing field or material properties. These models are built in time or frequency domain and can be interconnected to form quantum feedback networks. This review can be taken as a useful reference for engineers to understand the quantum physics behind, or for physicists to resolve control problems from a control engineering point of view.

关键词： quantum control Modelling quantum technology

Image charge effect on the light emission of rutile TiO2(110) induced by a scanning tunneling microscope

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Chinese Physics B 2018年第7期27卷 158-162页

作者： Chaoyu Guo Xiangzhi Meng Qin Wang Ying Jiang International center for quantum Materials School of Physics Peking University Beijing 100871 China Collaborative Innovation center of quantum Matter Beijing 100871 China CAS center for Excellence in Topological quantum Computation University of Chinese Academy of Sciences Beijing 100049 China

The plasmon-enhanced light emission of rutile TiO2（110） surface has been investigated by a low-temperature scanning tunneling microscope （STM）. We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO2（110）. In contrast to the Au（111） surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO2. By performing differential conductance （dl/dV） measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO2（110） towards the Femi level （EF） during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.

关键词： scanning tunneling microscopy light emission TiO2 plasmon