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    06 July 2021 Volume 40 Issue 7
      
    Superconducting quantum bits
    SU Fei-fan¹, YANG Zhao-hua¹, ², FAN Heng¹, ², ZHAO Shi-ping¹, ²
    College Physics. 2021, 40(7):  1.  doi:10.16854 /j.cnki.1000-0712.210045
    Abstract ( 1483 )   PDF (482KB) ( 616 )  
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    With Google's successful demonstration of " quantum supremacy" in 2019,the research of

    supercon- ducting quantum computing is attracting more and more attention around the globe.

    Superconducting quantum bits ( qubits) are macroscopic devices with fundamental quantum

    properties such as energy-level quantization,quantum- state superposition and quantum-state

    entanglement. They provide an excellent platform for the studies in many fields such as

    quantum physics,atomic physics,quantum optics,quantum chemistry,quantum simulation,quantum

    computing,and so on. In this article,we discuss the basic principles and structures of the

    superconducting phase-, charge-,transmon-,and flux-type qubits,as well as their device

    design and fabrication process. We also present a brief introduction to the rich research

    areas based upon the superconducting qubit architecture.

    A new definition of Lie derivative
    HE Xiao-kai¹, CAO Zhou-jian²
    College Physics. 2021, 40(7):  8.  doi:10.16854 / j.cnki.1000-0712.210091
    Abstract ( 1691 )   PDF (160KB) ( 417 )  
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    Lie derivative is an important concept of differential geometry. It is widely used in

    mathematics and physics. The Lie derivative is defined through the push-forward and pull-back

    maps. In this paper,a new definition of Lie derivative is presented. Instead of the abstract

    maps,we firstly introduce the concept of an adapted coordinate

    system of a smooth vector field on a manifold. Then a new definition of Lie derivative is given

    based on an adapted coordinate. It can be shown easily that the new definition is independent of

    the specific choice of an adapted coordi-nate system. After that,we deduce the explicit expression of the Lie derivative in general

    coordinate system,which admits the same form as the Lie derivative definition in usual textbooks. Compared to the

    existing definition of Lie derivative in usual textbooks,our new definition is much easier for

    beginners to understand.

    Further study on vector properties of angular displacement
    WANG Jing-zhou
    College Physics. 2021, 40(7):  12.  doi:10.16854 / j.cnki.1000-0712.200488
    Abstract ( 984 )   PDF (244KB) ( 307 )  
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    Discussion on vector properties of angular physical quantity,through graphic

    comparison,or through formula calculation,many papers draw the conclusion that infinitesimal

    rotation is vector and finite rotation is not vector.Neither point out the physical

    fundamental reason. According to the invariance of physical quantity and the covariance of

    transformation,it is proved that the rotation vector is not true vector,that of the essential

    reason is the levorotation and dextrorotation of the coordinate system.

    One way to explain Ampere's circuital theorem
    GENG Zhi-hao
    College Physics. 2021, 40(7):  17.  doi:10.16854 / j.cnki.1000-0712.200446
    Abstract ( 927 )   PDF (271KB) ( 871 )  
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    A new distinct and concise method to demonstrate the Ampere’s circuital theorem

    is proposed for general physics course of non-physics majors.It is practibal to enhance

    students’comprehension of this theorem.

    Application of charge projection method in the study of charge distribution law of infinitely long conductor thin plate
    ZHOU Qun-yi¹, MO Yun-fei², ZHOU Li-li³, HOU Zhao-yang⁴
    College Physics. 2021, 40(7):  19.  doi:10.16854 /j.cnki.1000-0712.200545
    Abstract ( 843 )   PDF (596KB) ( 415 )  
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    Using the charge distribution law of a uniformly charged cylinder of infinite

    length and the field strength formula of an infinitely long charged straight line,and adopting

    the charge projection method,the surface charge distribution of a charged conductor of finite

    width and infinite length has been deduced. According to the principle of electric

    potential superposition,the electric potential integral formula is derived; using the relationship

    between field strength and electric potential,the integral formula of the two components of

    electric field strength is derived. The formula is dimensionless,and the values of the components

    of electric potential and field strength are calculated through numerical integration. The

    electric potential and field strength of the charged conductor sheet of finite width and infinite

    length are shown in the picture,and the two-dimensional equipotential lines and electric

    field lines are also drawn in the diagram,which fully shows the distribution law of field strength.

    Dirac δ-function and its related applications
    ZHENG Shen-zhou, KANG Xiu-ying
    College Physics. 2021, 40(7):  25.  doi:10.16854 /j.cnki.1000-0712.200456
    Abstract ( 3820 )   PDF (299KB) ( 883 )  
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    It is indicated that Dirac δ-function is a continuation of the discrete Kronecker

    δ-function,which plays an important role in both mathematics and physics. In this paper,the precise

    definition of Dirac δ-function is introduced based on the concept of generalized functions,and it

    is proved that the Dirac δ-function is not a usual function in the Lebesgue sense of local

    integrable one. To this end,the Dirac δ-function is here approximated in the sense of weak limit by

    making use of the sequences of the unit rectangle impulse functions,Gauss functions,Bell-

    shaped functions and Sinc-functions,respectively. In addition,it is checked that the Dirac

    δ-function is obtained as a generalized derivative of the Heaviside function,and its higher derivative is also shown.

    Moreover,the convo- lutions,scales,compound transformations,orthogonality and Comb Dirac functions are recalled,respectively. Fi- nally,the relationship between Dirac δ-function and generalized Fourier transform is introduced,and we present an application to solve the Dirichlet boundary value problem of the Poisson equation.

    Classical and quantum statistical distributions of harmonic oscillators
    KANG Lin-hui, ZHANG Lin
    College Physics. 2021, 40(7):  30.  doi:10.16854 / j.cnki.1000-0712.200508
    Abstract ( 1102 )   PDF (359KB) ( 594 )  
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    There are some differences and connections between classical statistics and quantum

    statistics,and they can be converted to each other under certain conditions. The harmonic

    oscillator model is very important in physics,for example,the movement of the harmonic

    oscillator state description,energy,and the uncertainty princi- ple,spatial distribution and

    probability distribution of the two kinds of statistical methods are compared and summa-

    rized,respectively. The classical statistics of harmonic oscillator and the similarities and

    differences with quantum statistical distribution are deepened to the further understanding of

    quantum dynamics behavior and cognition.

    A new data processing method for Newton ring interference experiment
    HUA Xiao-bin, HUA Shi-qun
    College Physics. 2021, 40(7):  35.  doi:10.16854 / j.cnki.1000-0712.200471
    Abstract ( 1703 )   PDF (213KB) ( 1392 )  
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    Based on Newton’s ring interference experiment,the air layer thickness difference

    in the vertical direction between two adjacent interference rings is half wavelength. By

    taking the diameters of interference rings measured by moving reading microscope as

    horizontal coordinates,and taking the air layer thickness differences de- termined by the order

    difference of interference rings as longitudinal coordinates,the large circle equation of

    the planoconvex lens sphere in Newton’s ring device can be fitted and used to obtain the

    curvature radius of the plano- convex lens sphere. The experimental results show that the

    new experimental data processing method needs less measuring points,the process is simple and

    the results are reliable.

    Demonstration instrument for vacuum measurement
    WU Yuan, GUO Chao-xiu, YIN Ya-ling, CHEN Li-qing
    College Physics. 2021, 40(7):  38.  doi:10.16854 / j.cnki.1000-0712.200380
    Abstract ( 1171 )   PDF (293KB) ( 517 )  
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    The difference between quantum mechanics and classical physics is that the energy of the

    vacuum is not zero. Normally,due to the small energy,it is hard to measure the vacuum field

    directly only when the quantum measurement,such as homodyne detection,is used. Meanwhile,there is

    a lack of the experimental demonstration based on quantum measurement in college physics,which

    makes the theory of quantum mechanics hard to be un- derstanded. In this paper,a

    demonstration instrument for vacuum measurement based on homodyne detection is pro- posed. This

    instrument is simple in principle,intuitive in phenomenon,easy to operate and maintain. It makes

    up for the blank of quantum mechanics experiment in college physics,which realizes the expansion of

    frontier physics in college physics teaching.

    Observation and research on bands in metal tube
    WANG Zi-yan¹, WU Xiang², LU Jian-long³
    College Physics. 2021, 40(7):  41.  doi:10.16854 / j.cnki.1000-0712.200364
    Abstract ( 775 )   PDF (406KB) ( 199 )  
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    Looking into a cylindrical metal tube with smooth inner walls,bands with discontinuous

    distribution of brightness can be found. The basic principle of this phenomenon is preliminarily

    verified by mirrors. In this pa- per,the basic principle of the phenomenon is explained by

    establishing the model and using MATLAB to simulate. Finally,the combination of experiment and

    simulation is used to explore the series of factors which affect the phe- nomenon.

    Application of relativistic effect experimental spectrometer in thickness measurement
    CHEN Xu-yan, WANG Yun-qiao, CHENG Min-xi
    College Physics. 2021, 40(7):  47.  doi:10.16854 / j.cnki.1000-0712.190580
    Abstract ( 786 )   PDF (274KB) ( 163 )  
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    The relativistic effect experimental spectrometer can be used to verify the

    relativistic relationship conveniently and accurately between the energy and momentum of

    fast electrons. Two comprehensive experiments are carried out to measure the thickness of

    aluminum sheet and foil respectively. It can not only help students to un- derstand the nuclear

    physics experimental technology and applications,but also achieve the multiple applications of

    instruments,and improve using efficiency.

    Development and application of physical animation based on HTML5 technology
    SONG Hong-xiao¹, ZHANG Qi-wei², LIU Jian-qiang¹
    College Physics. 2021, 40(7):  51.  doi:10.16854 / j.cnki.1000-0712.210005
    Abstract ( 922 )   PDF (309KB) ( 226 )  
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    With mobile devices such as mobile phones replaced computers as the mainstream

    way of surfing the internet,the Flash animation that is currently used in college physics online

    learning,is required to be migrated to mobile devices in order to meet the needs of using mobile

    devices for learning. HTML5( H5 for short) is currently the best substitution of Flash. Based

    on the design and development practice of H5 animation in the new physics textbooks,in

    this article,the design ideas and development steps of physics h5 animation is summarized,the

    two steps of topic selection and physical modeling and interface and interactive function design in

    detail with examples is described.

    Practical research on the application of mind map in university science courses teaching—taking the course “Introduction to laser technology”as an example
    LI Hong-yu¹, XU Lin-xin², Hou Dan¹
    College Physics. 2021, 40(7):  55.  doi:10.16854 / j.cnki.1000-0712.200458
    Abstract ( 942 )   PDF (467KB) ( 222 )  
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    Through tutoring students to preview,arranging homework and collecting feedback

    in teaching the course of introduction to laser technology,the teacher let students freely choose

    whether to use mind map or not to complete homework and gradually guided students to try to use

    it to summarize knowledge points. These measures stimulated students’interest in applying

    mind map as a learning tool,and also made students’enthusiasm improved in learning the course of

    introduction to laser technology. It is also found that the mode of mind map plus notes not only

    took advantages of mind map to help clarify knowledge context,but also remedied the shortcomings

    that mind map could not show the specific content of knowledge points with notes.

    Therefore,this mode is more suitable for the study of physics subjects when compared with the

    simple mind map mode.

    The practical effect of online-offline blending teaching mode for large-class
    SUN Yan-yun, XU Li-hua, HE Yu, WU Lang, LIAO Wen-qiang, HUANG Xi-chen
    College Physics. 2021, 40(7):  61.  doi:10.16854 / j.cnki.1000-0712.200422
    Abstract ( 697 )   PDF (415KB) ( 167 )  
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    Based on the teaching practice,the effect of online- offline blending teaching

    mode is discussed, and some countermeasures and suggestions are also put forward. The

    statistical data show that the class in blending teaching mode has the characteristics of a low

    dispersion degree of score distribution and a high pass rate. It also in- dicates that the students

    who paid more attention to previewing would most likely gain a better learning effect. The

    research shows that it is difficult to meet the needs of students in different levels in a

    large class if only providing one set of online-video-resources. Therefore,diversified

    teaching strategies based on respecting different learning styles should be formulated. The

    consubstantial trend of course assignments restricted learning improving,and this phenomenon

    required the solid construction of FWA Education,which is known as full - scale

    education,whole- process education,all-around education. The deep application of online-offline

    blending teaching mode for large- class depends on the modern educational technology

    improvements,which could judge and feedback the subjective questions automatically. The evaluation

    scheme of blending teaching mode should also be optimized in the view of the education

    target of FWA Education.

    Three-dimensional simulation and visualization of the motion of rigid body and discussion on physical pendulum related problems
    LIN Jiong-hui¹, LIU Yu-ying², SONG Min²
    College Physics. 2021, 40(7):  68.  doi:10.16854 / j.cnki.1000-0712.200404
    Abstract ( 1028 )   PDF (710KB) ( 712 )  
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    In this paper,the rotational motion of rigid body around a fixed axis is studied by

    using Newton’s second law for rotation and in angular form with VPython software. Some

    special examples discussed in detail are motions of rotating uniformly rod under different

    torques,the path,angular displacement,angular velocity and mov- ing process,and were visualized

    intuitively in real time. The conservation of the energy of rotating rigid rod only ex- perienced

    with torque of gravity can be verified by VPython software. The plane motion of rigid

    body ( translation plus rotation) and vibration of rigid body are also studied. Especially,the

    chaos state of rigid rod with large rotating angle is investigated. The simulation deepens the

    understanding of textbook knowledge.

    Dynamic analysis of dancing coin
    HU Li
    College Physics. 2021, 40(7):  75.  doi:10.16854 / j.cnki.1000-0712.200366
    Abstract ( 1403 )   PDF (244KB) ( 997 )  
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    From the perspective of dynamics,this paper conducts a theoretical analysis on the third

    problem of the 2018 International Young Physicists’Tournament ( IYPT2018) ,“Dancing Coin”,and

    obtains the change in the height of the coin over time during a single beating. At the

    same time,the concept of “place error”is pro- posed,and the influence of coin place error

    on the coin’s tilting height is further discussed. It is found that the greater the

    place error,the faster the coin will rotate and the greater the maximum height of the

    coin will be reached. In the experiment,the process of coin dancing under different place

    errors was recorded with a high-speed camera,and software tracker was used to track. The

    comparison between the experimental results and the theoretical model verifies the

    correctness of the theoretical model.

    Theoretical models and an imaging experiment of the laser speckle drift phenomenon
    GUO You-xi, HE Yun-bo, LIU Rong-zhen, GONG Dian-jin-feng, XIA Cheng-jie
    College Physics. 2021, 40(7):  78.  doi:10.16854 / j.cnki.1000-0712.200524
    Abstract ( 989 )   PDF (511KB) ( 658 )  
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    A numerical method of calculating objective and subjective laser speckle

    patterns are developed based on the principles of Fourier optics. Expressions for the drift

    velocities of laser speckle and light spot in a sub- jective pattern are derived based on

    geometrical optical principles. Devices of imaging experiments are set up to ob- serve the

    objective and subjective laser speckle patterns and their respective drift phenomena. Methods

    to quantify the drift velocities of speckles and spots are established based on image processing

    techniques,which combine cor- relation function,the Fast Fourier Transform algorithm and

    convolution theorem. Both experimental and numerical results match perfectly with our

    theoretical expressions,which validates the numerical method and geometrical opti- cal model. This

    work provides a systematic method to research and an intuitive way to understand the laser speckle

    drift phenomenon.