分类: 物理学 >> 基本粒子与场物理学 提交时间: 2020-09-17
摘要: In this work, we try to find a way to describe the physical law of micro-world under the frame of a space-time theory. By introducing a scalar field D(x), we rewrite the action of conventional field theory and the Lagrangian describing the motion of the particle, where a modified space-time relation is obtained. To prove the correctness of this attempt, we derive the Klein-Gordon equation by the Hamilton-Jacobi method in four dimensional form.
分类: 物理学 >> 地球物理学、天文学和天体物理学 分类: 天文学 >> 星系和宇宙学 提交时间: 2020-09-09
摘要: Motivated by recent work on rotating black hole shadow [Phys. Rev. D101, 084029 (2020)], we investigate the shadow behaviors of rotating Hayward-de Sitter black hole for static observers at a finite distance in terms of astronomical observables. This paper uses the newly introduced distortion parameter in [arXiv:2006.00685] to describe the shadow's shape quantitatively. We show that the spin parameter would distort shadows and the magnetic monopole charge would increase the degree of deformation. At the same time, the distortion could be relieved because of the cosmological constant and the distortion would increase with the distance from the black hole. Besides, the spin parameter, magnetic monopole charge and cosmological constant increase will cause the shadow to shrink.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2020-09-06
摘要: We regard the background of space-time as a physical system composed of discrete volume elements at the Planck scale and get the internal energy of space-time by Debye model. A temperature-dependent minimum energy limit of the particles is proposed from the thermal motion part of the internal energy. As decreases of the temperature caused by the expansion of the universe, more and more particles would be "released" because of the change of the energy limit, we regard these new particles as a source of dark energy. The minimum energy limit also leads to a corrected number of particles in universe and a modified conservation equation. According to the modified conservation equation, an effective cosmological constant consistent with its observed value is obtained.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The frequency and orbital angular momentum (OAM) are independent physical properties of light that both offer unbounded degrees of freedom. However, creating, processing, and detecting high-dimensional OAM states have been a pivot and long-lasting task, as the complexity of the required optical systems scales up drastically with the OAM dimension. On the other hand, mature toolboxes -- such as optical frequency combs -- have been developed in the frequency domain for parallel measurements with excellent fidelity. Here we correlate the two dimensions into an equidistant comb structure on a photonic chip. Dissipative optical solitons formed in a nonlinear microresonator are emitted through the engraved angular gratings with each comb line carrying distinct OAM. Such one-to-one correspondence between the OAM and frequencies manifests state-of-the-art extinction ratios over 18.5 dB, enabling precision spectroscopy of optical vortices. The demonstrated vortex soliton microcombs provide coherent light sources that are multiplexed in the spatial and frequency domain, having the potential to establish a new modus operandi of high-dimensional structured light.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Microcombs are revolutionizing optoelectronics by providing parallelized, mutually coherent wavelength channels for time-frequency metrology and information processing. To implement this essential function in integrated photonic systems, it is desirable to drive microcombs directly with an on-chip laser in a simple and flexible way. However, two major difficulties are preventing this goal: 1) generating mode-locked comb states usually requires a significant amount of pump power and 2) the requirement to align laser and resonator frequency significantly complicates operation and limits the tunability of the comb lines. Here, we address these problems by using microresonators on an AlGaAs on-insulator platform to generate dark-pulse microcombs. This highly nonlinear platform dramatically relaxes fabrication requirements and leads to a record-low pump power of less than 1 mW for coherent comb generation. Dark-pulse microcombs facilitated by thermally-controlled avoided mode-crossings are accessed by direct DFB laser pumping. Without any feedback or control circuitries, the comb shows good coherence and stability. This approach also leads to an unprecedented wide chirping range of all the comb lines. Our work provides a route to realize power-efficient, simple and reconfigurable microcombs that can be seamlessly integrated with a wide range of photonic systems.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Optical microresonators with high quality ($Q$) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator $Q$ factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of $Q$, the ultimate attainable $Q$, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited $Q$ factors in several photonic material platforms. High-$Q$ microresonators are fabricated from thin films of SiO$_2$, Si$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. By using cavity-enhanced photothermal spectroscopy, the material-limited $Q$ is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate $Q$ vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.