查看更多>>摘要：We investigate the polarization properties of harmonics from the cyclic H32+molecular ions in tailored bichromatic counter-rotating circularly polarized(BCCP)fields by solving the time-dependent Schrödinger equation.The allowed harmonics and their helicities are associated with the symmetry compatibility of the field-target systems,and large intensity difference between adjacent harmonics with opposite helicities appears in a wide spectral range when the BCCP field is at certain rotation angles.We try to explain the intensity difference by using a recombination model based on the quantum-orbit theory and by analyzing the ionization pathways.Moreover,to synthesize attosecond pulse trains with tunable polarization,the intensity difference is manipulated by introducing a seed XUV field,and by changing the relative amplitude ratio as well as the helicity of BCCP fields.
查看更多>>摘要：Cyclo[18]carbon has received considerable attention thanks to its novel geometric configuration and special electronic structure.Superalkalis have low ionization energy.Doping a superalkali in cyclo[18]carbon is an effective method to improve the optical properties of the system because considerable electron transfer occurs.In this paper,the geometry,bonding properties,electronic structure,absorption spectrum,and nonlinear optical(NLO)properties of superalkaline M3O(M=Li,Na)-doped cyclo[18]carbon were studied by using density functional theory.M3O and the C18 rings are not coplanar.The C18 ring still exhibits alternating long and short bonds.The charge transfer between M3O and C18 forms stable[M3O]+[C18]-ionic complexes.C18M3O(M=Li,Na)shows striking optical nonlinearity,i.e.,their first-and second-order hyperpolarizability(βvec and γ||)increase considerably at λ=1907 nm and 1460 nm.
查看更多>>摘要：The recently developed magic-intensity trapping technique of neutral atoms efficiently mitigates the detrimental effect of light shifts on atomic qubits and substantially enhances the coherence time.This technique relies on applying a bias magnetic field precisely parallel to the wave vector of a circularly polarized trapping laser field.However,due to the presence of the vector light shift experienced by the trapped atoms,it is challenging to precisely define a parallel magnetic field,especially at a low bias magnetic field strength,for the magic-intensity trapping of 85Rb qubits.In this work,we present a method to calibrate the angle between the bias magnetic field and the trapping laser field with the compensating magnetic fields in the other two directions orthogonal to the bias magnetic field direction.Experimentally,with a constant-depth trap and a fixed bias magnetic field,we measure the respective resonant frequencies of the atomic qubits in a linearly polarized trap and a circularly polarized one via the conventional microwave Rabi spectra with different compensating magnetic fields and obtain the corresponding total magnetic fields via the respective resonant frequencies using the Breit-Rabi formula.With known total magnetic fields,the angle is a function of the other two compensating magnetic fields.Finally,the projection value of the angle on either of the directions orthogonal to the bias magnetic field direction can be reduced to 0(4)° by applying specific compensating magnetic fields.The measurement error is mainly attributed to the fluctuation of atomic temperature.Moreover,it also demonstrates that,even for a small angle,the effect is strong enough to cause large decoherence of Rabi oscillation in a magic-intensity trap.Although the compensation method demonstrated here is explored for the magic-intensity trapping technique,it can be applied to a variety of similar precision measurements with trapped neutral atoms.
查看更多>>摘要：We report a detailed study of magnetically levitated loading of ultracold 133Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane.The magnetic levitation for the 133Cs atoms forms an effective potential for a large number of atoms in a high spatial density.Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic field gradient and bias field is in good agreement with the theoretical analysis.This method has been widely used to obtain the Bose-Einstein condensation atoms for many atomic species.
查看更多>>摘要：A flexible extra broadband metamaterial absorber(MMA)stacked with five layers working at 2 GHz-40 GHz is in-vestigated.Each layer is composed of polyvinyl chloride(PVC),polyimide(PI),and a frequency selective surface(FSS),which is printed on PI using conductive ink.To investigate this absorber,both one-dimensional analogous circuit analy-sis and three-dimensional full-wave simulation based on a physical model are provided.Various crucial electromagnetic properties,such as absorption,effective impedance,complex permittivity and permeability,electric current distribution and magnetic field distribution at resonant peak points,are studied in detail.Analysis shows that the working frequency of this absorber covers entire S,C,X,Ku,K and Ka bands with a minimum thickness of 0.098λmax(λmax is the maximum wave-length in the absorption band),and the fractional bandwidth(FBW)reaches 181.1％.Moreover,the reflection coefficient is less than-10 dB at 1.998 GHz-40.056 GHz at normal incidence,and the absorptivity of the plane wave is greater than 80％when the incident angle is smaller than 50°.Furthermore,the proposed absorber is experimentally validated,and the experimental results show good agreement with the simulation results,which demonstrates the potential applicability of this absorber at 2 GHz-40 GHz.
查看更多>>摘要：Active metasurfaces with dynamically reconfigurable functionalities are highly demanded in various practical appli-cations.Here,we propose a wideband low-scattering metasurface that can realize an in-band reconfigurable transparent window by altering the operation states of the PIN diodes loaded on the structures.The metasurface is composed of a band-pass frequency selective surface(FSS)sandwiched between two polarization conversion metasurfaces(PCMs).PIN diodes are integrated into the FSS to switch the transparent window,while a checkerboard configuration is applied in PCMs for the diffusive-reflective function.A sample with 20x20 elements is designed,fabricated,and experimentally verified.Both simulated and measured results show that the in-band functions can be dynamically switched between beam-splitting scattering and high transmission by controlling the biasing states of the diodes,while low backscattering can be attained outside the passband.Furthermore,the resonant structures of FSS also play the role of feeding lines,thus significantly eliminating extra interference compared with conventional feeding networks.We envision that the proposed metasurface may provide new possibilities for the development of an intelligent stealth platform and its antenna applications.
查看更多>>摘要：A compound varifocal lens based on electromagnetic drive technology is designed and fabricated,where the poly-dimethylsiloxane(PDMS)film acts as a driving component,while the PDMS biconvex lens and the plane-concave lens form a coaxial compound lens system.The plane-concave lens equipped with driving coils is installed directly above the PDMS lens surrounded by the annular magnet.When different currents are applied,the annular magnet moves up and down,driving the PDMS film to undergo elastic deformation,and then resulting in longitudinal movement of the PDMS lens.The position change of the PDMS lens changes the focal length of the compound lens system.To verify the feasibil-ity and practicability of this design,a prototype of our compound lens system is fabricated in experiment.Our proposed compound lens shows that its zoom ability reaches 9.28 mm when the current ranges from-0.20 A to 0.21 A.
查看更多>>摘要：A tightly linked dual ring antenna is designed,and it is specifically tailored for uniformly coupling the microwave magnetic field to the nitrogen-vacancy(NV)center.The designed antenna operates at a center frequency of about 2.87 GHz,with a bandwidth of around 200 MHz,allowing it to address multiple resonance peaks in the optically detected magnetic resonance(ODMR)spectrum in an external magnetic field.Moreover,the antenna generates a fairly uniform magnetic field in a range with a radius of 0.75 mm.High resolution imaging of the magnetic field distribution on the surface of the antenna is conducted by using a fiber diamond probe.We also investigate the effect of magnetic field uniformity on the linewidth of ODMR,so as to provide insights into reducing the inhomogeneous broadening of ODMR.
查看更多>>摘要：We present an optimal and robust quantum control method for efficient population transfer in asymmetric double quantum-dot molecules.We derive a long-duration control scheme that allows for highly efficient population transfer by accurately controlling the amplitude of a narrow-bandwidth pulse.To overcome fluctuations in control field parameters,we employ a frequency-domain quantum optimal control theory method to optimize the spectral phase of a single pulse with broad bandwidth while preserving the spectral amplitude.It is shown that this spectral-phase-only optimization approach can successfully identify robust and optimal control fields,leading to efficient population transfer to the target state while concurrently suppressing population transfer to undesired states.The method demonstrates resilience to fluctuations in con-trol field parameters,making it a promising approach for reliable and efficient population transfer in practical applications.
查看更多>>摘要：The perfect hybrid vector vortex beam(PHVVB)with helical phase wavefront structure has aroused significant con-cern in recent years,as its beam waist does not expand with the topological charge(TC).In this work,we investigate the spatial quantum coherent modulation effect with PHVVB based on the atomic medium,and we observe the absorption char-acteristic of the PHVVB with different TCs under variant magnetic fields.We find that the transmission spectrum linewidth of PHVVB can be effectively maintained regardless of the TC.Still,the width of transmission peaks increases slightly as the beam size expands in hot atomic vapor.This distinctive quantum coherence phenomenon,demonstrated by the inter-action of an atomic medium with a hybrid vector-structured beam,might be anticipated to open up new opportunities for quantum coherence modulation and accurate magnetic field measurement.
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