Phase-matching quantum key distribution with imperfect sources

The huge discrepancies between actual devices and theoretical assumptions severely threaten the security of quantum key distribution.Recently,a general new framework called the reference technique has attracted wide attention in defending against the imperfect sources of quantum key distribution.Here,the state preparation flaws,the side channels of mode dependencies,the Trojan horse attacks,and the pulse classical correlations are studied by using the reference technique on the phase-matching protocol.Our simulation results highlight the importance of the actual secure parameters choice for transmitters,which is necessary to achieve secure communication.Increasing the single actual secure parameter will reduce the secure key rate.However,as long as the parameters are set properly,the secure key rate is still high.Considering the influences of multiple actual secure parameters will significantly reduce the secure key rate.These actual secure parameters must be considered when scientists calibrate transmitters.This work is an important step towards the practical and secure implementation of phase-matching protocol.In the future,it is essential to study the main parameters,find out their maximum and general values,classify the multiple parameters as the same parameter,and give countermeasures.

Noncollinear phase-matching geometries in ultra-broadband quasi-parametric amplification

Optical parametric chirped pulse amplification(OPCPA)shows great potential in producing ultrashort high-intensity pulses because of its large gain bandwidth.Quasi-parametric chirped pulse amplification(QPCPA)may further extend the bandwidth.However,behavior of QPCPA at a limited pump intensity(e.g.,≤5 GW/cm^(2) in a nanosecond pumped QPCPA)has not yet been investigated fully.We discuss detailedly the ultra-broadband amplification and the noncollinear phasematching geometry in QPCPA,model and develop a novel noncollinear geometry in QPCPA,namely triple-wavelength phase-matching geometry,which provides two additional phase-matching points around the phase-matching point at the central wavelength.Our analysis demonstrates that the triple-wavelength phase-matching geometry can support stable,ultra-broadband amplification in QPCPA.The numerical simulation results show that ultrashort pulse with a pulse duration of 7.92 fs can be achieved in QPCPA when the pump intensity is limited to 5 GW/cm^(2),calculated using the nonlinear coefficient of YCa;O(BO;);.

Phase-matching quantum key distribution with light source monitoring

The transmission loss of photons during quantum key distribution(QKD)process leads to the linear key rate bound for practical QKD systems without quantum repeaters.Phase matching quantum key distribution(PM-QKD)protocol,an novel QKD protocol,can overcome the constraint with a measurement-device-independent structure,while it still requires the light source to be ideal.This assumption is not guaranteed in practice,leading to practical secure issues.In this paper,we propose a modified PM-QKD protocol with a light source monitoring,named PM-QKD-LSM protocol,which can guarantee the security of the system under the non-ideal source condition.The results show that our proposed protocol performs almost the same as the ideal PM-QKD protocol even considering the imperfect factors in practical systems.PMQKD-LSM protocol has a better performance with source fluctuation,and it is robust in symmetric or asymmetric cases.

Phase-Matching and Parametric Conversion for the Mid-Infrared in As₂S₃Waveguides

We illustrate two As2S3 waveguide designs for four-wave mixing, which can generate 3.03 μm mid-infrared light from a 1.55 μm near-infrared signal source and a 2.05 μm pump source. Through simulations, we verify that four-wave mixing phase-matching efficiencies up to 100% can be achieved using dispersion engineering to maintain the dispersion at 2.05 μm near to zero. The best conversion efficiency is –10 dB. When the waveguide length is 1 cm, the parametric conversion bandwidth is 1525 nm. We also evaluated the shift of 100% phase-matching efficiency wavelengths based upon fabrication tolerances.

Non-collinear nonlinear properties of steel and LY12 aluminum alloy

The sensitivity of collinear nonlinear nondestructive testing technique based on harmonic detection is high,but the results are vulnerable to interference from other nonlinear of experiment sources,which leads to this technology limited in industrial applications.To solve this problem,a non-collinear nonlinear ultrasonic testing experimental system is established based on non-collinear beam mixing technology.The non-collinear nonlinear response is observed in the steel and LY12 aluminum alloy.The results show that:1 Based on the benefits of space selection,mode conversion,frequency and steerable optional of non-collinear beam mixing technology,the interference of system nonlinear effects can be suppressed effectively;2 Mode conversion and beam mixing are present in steel and LY12 aluminum alloy,and the non-collinear non-linear response of LY12 aluminum alloy is stronger than steel and the measurement results are more obvious;3 The technology has the feasibility to evaluate the uniformity of material internal.

Spectrum Correction in Study of Solvation Dynamics by Fluorescence Non-collinear Optical Parametric Amplification Spectroscopy

Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spec- troscopy can extract the curve of spectral gain from its parametric superfluorescence. This unique spectrum correction method enables fluorescence non-collinear optical parametric amplification spectroscopy acquiring the genuine transient fluorescence spectrum of the studied system. In this work we employ fluorescence non-collinear optical parametric amplification spectroscopy technique to study the solvation dynamics of DCM dye in ethanol solution, and confirm that genuine solvation correlation function and shift of peak frequency can be derived from transient fluorescence spectra after the spectral gain correction. It demonstrates that fluorescence non-collinear optical parametric amplification spectroscopy can benefit the research fields, which focuses on both fluorescence intensity dynamics and fluorescence spectral shape evolution.

Frequency dependence of quantum path interference in non-collinear high-order harmonic generation

High-order harmonic generation（HHG） driven by two non-collinear beams including a fundamental and its weak second harmonic is numerically studied. The interference of harmonics from adjacent electron quantum paths is found to be dependent on the relative delay of the driving pulse, and the dependences are different for different harmonic orders.This frequency dependence of the interference is attributed to the spatial frequency chirp in the HHG beam resulting from the harmonic dipole phase, which in turn provides a potential way to gain an insight into the generation of high-order harmonics. As an example, the intensity dependent dipole phase coefficient α is retrieved from the interference fringe.

Out-of-plane weak ferromagnetism at room temperature in lattice-distortion non-collinear antiferromagnet of single-crystal Mn_(3)Sn

Out-of-plane weak ferromagnetic(OWFM)spin arrangements with topological properties can realize a series of interesting physical properties.However,this spin structure tends to exist at low temperatures.The OWFM structure can also be induced at room temperature by hydrostatic pressure,whereas this isotropic approach tends to form helical AFM structures.We report the OWFM spin arrangement in single crystal Mn_(3)Sn by an anisotropic strategy of high-stressconstrained compression deformation at room temperature.Both experimental and theoretical simulation results show that the alignment of the OWFM spin structure is due to the distortion of the atomic scale caused by the strain energy during deformation.The OWFM spin arrangement can significantly change the magnetic property of Mn_(3)Sn.As a result,the remanent magnetization M_(r)for the deformed sample(0.056μ_(B)/f.u.)is about eleven times that for the pre-deformed sample(0.005μ_(B)/f.u.),and the coercivity(H_(c))increases from 0 k Oe(pre-deformed sample)to 6.02 k Oe(deformed sample).Our findings provide a way to generate the OWFM spin structure at room temperature and may give fresh ideas for creating antiferromagnetic materials with excellent physical properties.

Lasing dynamics study by femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy

Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy （FNOPAS） is a versatile technique with advantages of high sensitivity, broad detection bandwidth, and intrinsic spectrum correction func- tion. These advantages should benefit the study of coherent emission, such as measurement oflasing dynamics. In this letter, the FNOPAS was used to trace the lasing process in Rhodamine 6G （R6G） solution and organic semiconductor nano-wires. High-quality transient emission spectra and lasing dynamic traces were acquired, which demonstrates the applicability of FNOPAS in the study of lasing dynamics. Our work extends the application scope of the FNOPAS technique.

Controllable transitions among phase-matching conditions in a single nonlinear crystal

Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.

New phase-matching selection rule to generate angularly isolated harmonics

High harmonic generation(HHG)is an ideal probing source.In general,all harmonics are coupled with the corresponding input laser when generated,and for applications,they are separated using additional spectrometers.Herein,we report the angular isolation of relativistic harmonics at a predicted emission angle upon generation and,most importantly,a new phase-matching chain selection rule is derived to generate harmonics.Based on the laser plasma mechanism involving two non-collinear relativistic driving lasers,the nth harmonic carrying the information of both input lasers originates from its adjacent(n–1)th harmonic coupled with one of the input lasers.Meanwhile,the intensity and emission angle of the generated isolated harmonic are both greatly increased compared with those in the gas scheme.These results are satisfactorily verified by theoretical analysis and three-dimensional particle-in-cell simulations,which have physical significance and are essential for practical applications.

Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

An asymmetric quantum well （AQW） is designed to emit terahertz （THz） waves by using difference frequency generation （DFG） with the structure of GaAs/Al0.2Ga0.8As/Al0.5Ga0.sAs. The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail. We find that the absorption coefficients vary with the two pump optical intensities, and they reach the maxima when the pump wavelengths are given as λp1 = 9.70 μm and λp2 = 10.64 μm, respectively. Compared with non-parabolic conditions, the total absorption coefficient under parabolic conditions shows a blue shift, which is due to the increase in the energy difference between the ground and excited states. By adjusting the two pump optical intensities, the wave vector phase-matching condition inside the AQW is satisfied.

Tunable Terahertz Source Based on Optics Pumped Nonlinear Crystals

Recent progresses about optical pumped tunable terahertz （THz） sources are interviewed, including THz parametric oscillation （TPO） and difference frequency generation （DFG）. We develop high efficiency and high power surface-emitted TPO, as well as DFG with nonlinear crystals. A novel scheme for the high efficiency DFG source based on the Cherenkov phase-matching technology is comprehensively investigated in both bulk crystals. The widely tunable optical THz radiation is also researched based on the organic nonlinear 4-N,N-dimethylamino-4＇-N＇- methylstilbazolium 2,4,6-trimethylbenzenesulfonate （DSTMS） crystal.

Giant topological Hall effect of ferromagnetic kagome metal Fe3Sn2

We present the experiment observation of a giant topological Hall effect(THE)in a frustrated kagome bilayer magnet Fe3Sn2.The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K.Its maximum absolute value reaches^2.01μΩ·cm at 300 K and 0.76 T.The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration,possibly related to the magnetic frustration interaction in Fe3Sn2.

Topological magnetotransport and electrical switching of sputtered antiferromagnetic Ir_(20)Mn_(80)

Topological magnetotransport in non-collinear antiferromagnets has attracted extensive attention due to the exotic phenomena such as large anomalous Hall effect(AHE),magnetic spin Hall effect,and chiral anomaly.The materials exhibiting topological antiferromagnetic physics are typically limited in special Mn_3X family such as Mn_3Sn and Mn_3Ge.Exploring the topological magnetotransport in common antiferromagnetic materials widely used in spintronics will not only enrich the platforms for investigating the non-collinear antiferromagnetic physics,but also have great importance for driving the nontrivial topological properties towards practical applications.Here,we report remarkable AHE,anisotropic and negative parallel magnetoresistance in the magnetron-sputtered Ir_(20)Mn_(80)antiferromagnet,which is one of the most widely used antiferromagnetic materials in industrial spintronics.The ab initio calculations suggest that the Ir_4Mn_(16)(IrMn_4)or Mn_3Ir nanocrystals hold nontrivial electronic band structures,which may contribute to the observed intriguing magnetotransport properties in the Ir_(20)Mn_(80).Further,we demonstrate the spin–orbit torque switching of the antiferromagnetic Ir_(20)Mn_(80)by the spin Hall current of Pt.The presented results highlight a great potential of the magnetron-sputtered Ir_(20)Mn_(80)film for exploring the topological antiferromagnet-based physics and spintronics applications.

Polarisation-sensitive four-wave mixing and soliton self-frequency shift effect in the highly birefringent photonic crystal fibre

By adjusting the polarisation state of the pump at 805 nm parallel to slow （x） and fast （y） axes of the highly birefringent photonic crystal fibre with zero dispersion wavelengths 790 nm and 750 nm, this paper demonstrates the efficient polarisation-sensitive four wave mixing involved in pump, anti-Stokes and Stokes signals and soliton self- frequency shift effects induced by the phase-matching between red-shifted solitons and blue-shifted dispersive waves. If the reduction of coupling efficiency to the circular pump laser mode or other circular fibres due to asymmetry of the core is neglected, more than 98% of the total input power is kept in a single linear polarisation. Controlled dispersion characteristic of the doublet of fundamental guided-modes results in achieving light field strongly confined in principal axes of photonic crystal fibre, and enhancing the corresponding nonlinear-optical process through the remarkable nonlinear birefringence.

Tailoring OAM spectrum of high-order harmonic generation driven by two mixed Laguerre–Gaussian beams with nonzero radial nodes

The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we show that the OAM spectrum of vortex HHG can be readily tailored by varying the radial node(from 0 to 2)in the driving laser consisting of two mixed Laguerre-Gaussian(LG)beams.We find that due to the change in spatial profile of HHG,the distribution range of the OAM spectrum can be broadened and its shape can be modified by increasing the radial node.We also show that the OAM mode range becomes much wider and its distribution shape becomes more symmetric when the harmonic order is increased from the plateau to the cutoff when the driving laser has the nonzero radial nodes.Through the map of coherence length and the evolution of harmonic field in the medium,we reveal that the favorable off-axis phase-matching conditions are greatly modified due to the change of intensity and phase distributions of driving laser with the radial node.We anticipate this work to stimulate some interests in generating the XUV vortex beam with tunable OAM spectrum through the gaseous HHG process achieved by manipulating the mode properties of the driving laser beam.

Selection of odd or even harmonics by a multi-color laser field with macroscopic phase-matching

We experimentally and theoretically demonstrate that ＊~he property （odd or even） of generated harmonics can be selected by manipulating the macroscopic phase-matching conditions based on a three-color laser field. Only odd or even harmonics can be made dominant by changing the focal position and adjusting the gas pressure. These results indicate that the odd-even property of the generated harmonics can be controlled by using the mult i-color laser field with macroscopic phase-matching.

Manipulating non-collinear antiferromagnetic order and thermal expansion behaviors in triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N

Magnetic materials with non-collinear spin orderings provide an outstanding platform to probe spin-tronic phenomena owing to their strong spin-orbit coupling(SOC)and unique Berry phase.It is thus important to obtain a non-collinear antiferromagnetic(AFM)phase at room temperature(RT).Signifi-cantly,the discovery of novel materials with nearly zero thermal expansion(ZTE)property near RT is required and pursued for avoiding thermal stress and fracture in spintronic devices.Herein,the doping of Sn(Ge)at the Ag site in the triangular lattice Mn_(3)Ag_(1-x)Sn(Ge)_(x)N compounds increases effectively the Neel point and makes the interesting non-collinearГ^(5g)AFM phase exist above RT.The magnetic phase diagrams withГ^(5g)phase up to 498 K were built by the combined analysis of neutron powder diffraction(NPD),magnetic measurements,electronic transport,and differential scanning calorimetry(DSC).The thermal expansion behaviors of Mn_(3)Ag_(1-x)Sn(Ge)_(x)N were modulated,and the nearly ZTE above RT was achieved in Mn_(3)Ag_(0.5)Ge_(0.5)N withinГ^(5g)AFM ordering.Our findings offer an effective way to tailor the non-collinear AFM ordering and correlated thermal expansion behavior for potential use in the emerging field of thermal stress-free magnetic chip materials.

Atomically phase-matched second-harmonic generation in a 2D crystal

Second-harmonic generation(SHG)has found extensive applications from hand-held laser pointers to spectroscopic and microscopic techniques.Recently,some cleavable van der Waals(vdW)crystals have shown SHG arising from a single atomic layer,where the SH light elucidated important information such as the grain boundaries and electronic structure in these ultra-thin materials.However,despite the inversion asymmetry of the single layer,the typical crystal stacking restores inversion symmetry for even numbers of layers leading to an oscillatory SH response,drastically reducing the applicability of vdW crystals such as molybdenum disulfide(MoS_(2)).Here,we probe the SHG generated from the noncentrosymmetric 3R crystal phase of MoS_(2).We experimentally observed quadratic dependence of second-harmonic intensity on layer number as a result of atomically phase-matched nonlinear dipoles in layers of the 3R crystal that constructively interfere.By studying the layer evolution of the A and B excitonic transitions in 3R-MoS_(2) using SHG spectroscopy,we also found distinct electronic structure differences arising from the crystal structure and the dramatic effect of symmetry and layer stacking on the nonlinear properties of these atomic crystals.The constructive nature of the SHG in this 2D crystal provides a platform to reliably develop atomically flat and controllably thin nonlinear media.