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- 摘要
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- 实验方案
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Variational Solution of Steady-Structure in Exciton-Polariton Condensates with a Modified Lagrangian Approach
摘要： Exciton-polariton condensate is a new kind of system exhibiting spontaneous coherence, which is a new quantum dissipation system. Numerical simulation and analytical methods can be used to study the static and dynamical properties of exciton-polariton condensate. In this paper, A modified Lagrangian method is developed for exciton-polariton system to find the steady-state structure and regimes among the parameters of the system, and two new forms of trial wave function are proposed. The modified Lagrangian method is successfully applied to the exciton-polariton system described by the open-dissipative Gross-Pitaevskii equation for the first time. Furthermore, static version of the modified Lagrangian method provides stationary shape of the steady-state structure, while the time-dependent version can be used to study small amplitude oscillations around stationary states. On the one hand, comparison of the profiles for steady-state structure, predicted by the modified Lagrangian and those found from numerical solution of the open-dissipative Gross-Pitaevskii(dGP) equation shows good agreement, thereby proving the accuracy of the trial wave function and validating the proposed approach. Particularly, this new method promotes the deeper cognition and understanding for the dissipative exciton-polariton system and is helpful to explore the mechanism of the gain and dissipation effect on the steady-state structure of the system.
关键词： dissipative,Lagrangian method,trial wave function,exciton-polariton condensate,steady-state structure
更新于2025-09-23 15:22:29
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On the quantum-mechanics of a single photon
摘要： It is shown that a Dirac(-type) equation for a rank-two bi-spinor field ψph on Minkowski (configuration) spacetime furnishes a Lorentz-covariant quantum-mechanical wave equation in position-space representation for a single free photon. This equation does not encounter any of the roadblocks that have obstructed previous attempts (by various authors) to formulate a quantum-mechanical photon wave equation. In particular, it implies that the photon wave function ψph yields conserved non-negative Born-rule-type quantum probabilities and that its probability current density four-vector transforms properly under Lorentz transformations. Moreover, the eigenvalues of the pertinent photon Dirac Hamiltonian and the vector eigenvalues of the photon momentum operator yield the familiar Einstein relations E = ?ω and p = ?k, respectively. Furthermore, these spin-1 wave modes are automatically transversal without the need of an additional constraint on the initial data. Some comments on other proposals to set up a photon wave equation are supplied as well.
关键词： probability current,wave function,quantum-mechanics,photon,Dirac-type equation,Born-rule,Einstein relations,transversal modes,Lorentz-covariant
更新于2025-09-23 15:21:21
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Laser-Based Phase Contrast for Transmission Electron Microscopy
摘要： Laser control of free electrons has been used to advance the exploration of matter on the atomic scale. For example, temporal modulation of electron waves with light has enabled the study of transient processes with attosecond resolution. By contrast, laser-based spatial shaping of the electron wave function has not yet been realized, even though it could be harnessed to probe radiation-sensitive systems, such as biological macromolecules, at the standard quantum limit and beyond. We demonstrate increased image contrast by laser control of the spatial phase profile of the electron wave function in transmission electron microscopy (TEM). We first realize an electron interferometer, using continuous-wave laser-induced retardation to coherently split the electron beam, and capture TEM images of the light wave. We then demonstrate Zernike phase contrast by using the laser beam to shift the phase of the electron wave scattered by a specimen relative to the unscattered wave. Electrons interact with light via the repulsive ponderomotive potential arising from stimulated Compton scattering. Due to the short electron-light interaction time in a micron-scale laser focus, retardation of the relativistic electrons used in TEM requires an intensity of tens of GW/cm2. Such intensities have so far only been attained with pulsed lasers, but a cw laser is needed in order to work state-of-the-art, continuously operating TEM. The requisite laser intensity is generated by 4000-fold resonant power enhancement in a near-concentric Fabry-Perot optical cavity with a mode waist of w0 = 13 μm. A laser system consisting of a fiber amplifier seeded by a low-power master laser supplies an input laser beam at a wavelength of λ = 1064 nm. The experiments are carried out with 80 keV electrons, in a custom-modified TEM (FEI Titan) equipped with additional electron optics that magnify the diffraction pattern to an effective focal length of f = 20 mm. The cavity is suspended in the TEM column, with its axis orthogonal to the electron beam propagation direction and with the mode waist positioned close to the center of the magnified electron diffraction plane, as shown in Fig. 1. Zernike phase contrast is evident in a typical close-to-focus image (Fig. 1), showing the structure of the carbon film. A high-intensity CW laser field generates Zernike phase contrast in a TEM and significantly increases the image contrast at low spatial frequencies. Such a phase plate will enable dose-efficient data collection in single-particle analysis of biological macromolecules, electron tomography of vitrified cells, and imaging of sensitive materials science specimens. The controllable phase shift in this device can also be used for holographic reconstruction of the post-specimen wave function. Work in the immediate future will include working with 300-keV electrons, which requires constructing a new cavity with lower-loss optical coatings to reach higher laser intensity. We will also study and optimize the imaging properties of the phase-contrast TEM, and apply it to structural biology.
关键词： Zernike phase contrast,Laser control,Fabry-Perot optical cavity,Transmission Electron Microscopy,electron wave function
更新于2025-09-19 17:13:59
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European Microscopy Congress 2016: Proceedings || Tailoring the wave function of electron probes for the selective detection of plasmonic modes
摘要： The wave function of electron beams for the self-detection of plasmonic modes.
关键词： wave function,self-detection,electron beams,plasmonic modes
更新于2025-09-16 10:30:52
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Free Scattering Theory in Circularly Polarized Laser Field
摘要： In the present study, we have investigated scattering of an electron by hydrogen atoms in the presence of the Circularly Polarized (CP) laser field. We have discussed the polarization effect of laser field on hydrogen atom and effect of the resulted polarized potential on differential scattering cross section is studied. We assumed the scattered electrons having kinetic energy 100 eV because it permitted to treat the scattering process in first order Born Approximation. The scattering electron was described by Volkov wave function. We found the differential scattering cross section decreases with the increase in scattering angle, for a fixed value of a laser parameters and kinetic energy of an incident electron. From this study we found that, the differential scattering cross section for the electric field perpendicular to the direction of momentum transfer depends on the elastic scattering amplitude. Finally, we concluded that the differential scattering cross section greatly depends upon the polarization of the laser field.
关键词： Volkov Wave Function,Differential Scattering Cross section,Polarization
更新于2025-09-16 10:30:52
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Direct Measurement of a Nonlocal Entangled Quantum State
摘要： Entanglement and the wave function description are two of the core concepts that make quantum mechanics such a unique theory. A method to directly measure the wave function, using weak values, was demonstrated by Lundeen et al. [Nature 474, 188 (2011)]. However, it is not applicable to a scenario of two disjoint systems, where nonlocal entanglement can be a crucial element, since that requires obtaining weak values of nonlocal observables. Here, for the first time, we propose a method to directly measure a nonlocal wave function of a bipartite system, using modular values. The method is experimentally implemented for a photon pair in a hyperentangled state, i.e., entangled both in polarization and momentum degrees of freedom.
关键词： modular values,hyperentangled state,Entanglement,weak values,quantum mechanics,wave function
更新于2025-09-16 10:30:52
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Exploration of charge carrier delocalization in the iron oxide/CdS type-II heterojunction band alignment for enhanced solar-driven photocatalytic and antibacterial applications
摘要： Recyclable magnetic photocatalysts of iron oxide (IO)/CdS core/shell nanocrystals (CSNCs) were prepared by a facile sequential one-pot method using 3, 3'-thiobispropanoic acid (TDP) as a bridge. The CSNCs showed redshift in absorption edge, decrease in the optical band gap, reduced exciton decay rates and increment in particle size. Quenching studies have been employed to understand the position of the electron/hole wave-functions at the IO/CdS interface. Antimicrobial tests have also been performed using broth tube dilution and disc diffusion methods against S. aureus. Additionally, photocatalytic properties of IO/CdS CSNCs have been evaluated for the decomposition of xylenol blue. In comparison with CdS quantum dots (QDs) and iron oxide nanoparticles (IONPs), the IO/CdS CSNCs showed improved photocatalytic and bactericidal activities. Finally, levels of oxidative damage to proteins and lipids were evaluated.
关键词： Photocatalysis,Wave-function engineering,Advanced oxidation process,Iron oxide/CdS nanocrystals,Photocatalytic bacterial inactivation
更新于2025-09-04 15:30:14