Switchable vortex beam polarization state terahertz multi-layer metasurface

We propose a switchable vortex beam polarization state terahertz multi-layer metasurface,which consists of threelayer elliptical metal crosses,four-layer dielectrics,and two-layer hollow metal circles,which are alternately superimposed.Under the normal incidence of left-handed circularly polarized(LCP)wave and the right-handed circularly polarized(RCP)waves,the proposed structure realizes three independent control functions,i.e.,focused and vortex beam,vortex beam with different topological charges,and polarization states switching,and azimuth switching of two vortex beams with different polarization states.The results show that the proposed metasurface provides a new idea for investigating the multifunctional terahertz wave modulation devices.

Polarization scrambling characteristic analysis based on density of polarization states statistics

We report a new method to deeply analyze the scrambling characteristic of polarization scramblers based on density of polarization states(DPS)statistics that makes it possible to describe the DPS distribution in detail on the whole Poincarésphere,thus easy to locate accurately the nonuniform areas of defective polarization scramblers,which cannot be realized by existing methods.We have built a polarization scrambling system to demonstrate the advantages of our method compared with others by experiments and suggested effective evaluation indexes whose validity is well confirmed by applying to a commercial scrambler.Our conclusions are valuable for accurately analyzing and diagnosing the performance of any polarization scrambler,and quality evaluation of polarization controllers or other polarization devices.

Interpretation of the Entangled States

An interpretation of the entangled states is considered.Two-photon states of photon A on path a and photon B on path b with polarizations H,V are constructed.Two synchronized photons,1 and 2,can take the paths a and b,with equal probability 50%.In the bases a,b and H,V,the states of the photons form the product states.In the basis 1,2,the states of the photons form the entangled state.The states of the photons in the bases 1,2;a,b;H,V are inseparable.The correlation of the photons due to the entanglement in the basis 1,2 can be seen in the bases a,b and H,V.The interference term in the approach under consideration and in the standard approach is the same thus providing for the same correlation.

Recent advances of defect-induced spin and valley polarized states in graphene

Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,which can support a series of broken symmetry states.Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale,and hence,lead to rich quantum states,highlighting promising directions for spintronics and valleytronics.In this article,we mainly review the recent scanning tunneling microscopy(STM)advances on the spin and/or valley polarized states induced by an individual atomicscale defect in graphene,including a single-carbon vacancy,a nitrogen-atom dopant,and a hydrogen-atom chemisorption.Lastly,we give a perspective in this field.

Highly efficient vectorial field manipulation using a transmitted tri-layer metasurface in the terahertz band

Polarization is a basic characteristic of electromagnetic waves that conveys much optical information owing to its many states.The polarization state is manipulated and controlled for optical information security,optical encryption,and optical communication.Metasurface devices provide a new way to manipulate wave-fronts of light.A single ultrathin metasurface device can generate and modulate several differently polarized light fields,and thus carries optical information in several different channels.Terahertz(THz)waves have become widely used as carrier waves for wireless communication.Compact and functional metasurface devices are in high demand for THz elements and systems.This paper proposes a tri-layer metallic THz metasurface for multi-channel polarization generation and phase modulation with a high efficiency of approximately 80%.An azimuthally polarized THz vectorial beam generator is realized and characterized for use as a THz polarization analyzer.The incident polarization angle can be observed graphically with high accuracy.Moreover,a vectorial hologram with eight channels for different linear polarization states is demonstrated experimentally.The information in different holograms can be hidden by choosing the polarization channel for detection.This work contributes to achieving multi-functional metasurface in the THz band and can benefit THz communication and optical information security.

Measurement-device-independent one-step quantum secure direct communication

The one-step quantum secure direct communication(QSDC)(Sci.Bull.67,367(2022))can effectively simplify QSDC’s operation and reduce message loss.For enhancing its security under practical experimental condition,we propose two measurement-device-independent(MDI)one-step QSDC protocols,which can resist all possible attacks from imperfect measurement devices.In both protocols,the communication parties prepare identical polarization-spatial-mode two-photon hyperentangled states and construct the hyperentanglement channel by hyperentanglement swapping.The first MDI one-step QSDC protocol adopts the nonlinear-optical complete hyperentanglement Bell state measurement(HBSM)to construct the hyperentanglement channel,while the second protocol adopts the linear-optical partial HBSM.Then,the parties encode the photons in the polarization degree of freedom and send them to the third party for the hyperentanglementassisted complete polarization Bell state measurement.Both protocols are unconditionally secure in theory.The simulation results show the MDI one-step QSDC protocol with complete HBSM attains the maximal communication distance of about354 km.Our MDI one-step QSDC protocols may have potential applications in the future quantum secure communication field.

Abnormal intensity and polarization of Raman scattered light at edges of layered MoS_(2)

The edges of two-dimensional(2D)materials can exhibit special structure and thus distinctive properties differing from the interior,such as the modified photoluminescence emission,the improved electrocatalytic activity,and the enhanced nonlinear optical response.In this work,we report the observation of abrupt enhancement of Raman scattered light at edges of layered MoS_(2),which is closely related to the polarization of the incident light.More importantly,the intensity of out-of-plane A1g mode is enhanced much more obviously than the in-plane E_(2g)^(1)mode.The unique optical effect at edges is also reflected on the alteration of Raman selection rule.The forbidden Raman modes are observed at edge region,and the polarization of Raman scattered light can be modulated by the edge structure,which differs obviously from that of the interior.We attribute these particular performances to the modulation of the intensity and distribution of the electric field for the incident and Raman scattered light at the edge.This work provides a systematic research on the intensity and polarization modulation of the Raman scattering at edges,which would be helpful for understanding the distinctive optical properties of the edge structure.

Improved multiferroic in EuTiO_(3) films by interphase strain engineering

Interphase strain engineering provides a unique methodology to significantly modify the lattice structure across a single film,enabling the emergence and manipulation of novel functionalities that are inaccessible in the context of traditional strain engineering methods.In this work,by using the interphase strain,we achieve a ferromagnetic state with enhanced Curie temperature and a room-temperature polar state in EuO secondary phase-tunned EuTiO_(3) thin films.A combination of atomic-scale electron microscopy and synchrotron X-ray spectroscopy unravels the underlying mechanisms of the ferroelectric and ferromagnetic properties enhancement.Wherein,the EuO secondary phase is found to be able to dramatically distort the TiO_6 octahedra,which favors the non-centrosymmetric polar state,weakens antiferromagnetic Eu-Ti-Eu interactions,and enhances ferromagnetic Eu-O-Eu interactions.Our work demonstrates the feasibility and effectiveness of interphase strain engineering in simultaneously promoting ferroelectric and ferromagnetic performance,which would provide new thinking on the property regulation of numerous strongly correlated functional materials.

Experimental long-distance quantum secure direct communication

Quantum secure direct communication(QSDC) is an important quantum communication branch, which realizes the secure information transmission directly without encryption and decryption processes.Recently, two table-top experiments have demonstrated the principle of QSDC. Here, we report the first long-distance QSDC experiment, including the security test, information encoding, fiber transmission and decoding. After the fiber transmission of 0.5 km, quantum state fidelities of the two polarization entangled Bell states are 91% and 88%, respectively, which are used for information coding. We theoretically analyze the performance of the QSDC system based on current optical communication technologies,showing that QSDC over fiber links of several tens kilometers could be expected. It demonstrates the potential of long-distance QSDC and supports its future applications on quantum communication networks.

Compensating Large PMD by Four Free degrees in an OTDM System

In this paper, by introducing a two-stages polarization mode dispersion (PMD) compensator after a optical fiber link with a large PMD, we compensated over 270ps first-order and 2000ps2 high-order PMD in a optical fiber link with super high PMD. Our experimental results shows that, the compensators based on the two-stages of compensator can be used to PMD compensation in a 20Gb/s OTDM system with 60 km high PMD fiber. Before compensation, 270ps DGD is became into max. 7ps after compensation. At simultane...