Quantum nonlocal correlation is one of the most important characteristics to distinguish quantum mechanics from classical mechanics. Since it shows that two or more entangled particles will have a correlation with each other no matter how farapart they are. Quantum nonlocal correlation is the basis of quantum information technology such as quantum computing, quantumteleportation and quantum key distribution, so it is of great application signi?cance to test the quantum nonlocal correlation in thehierarchical environment. The Hardy-type paradox is an equation-free scheme for quantum nonlocal correlation testing, becausethe logic is no need for complex measurement in the experiment. Based on the Hardy-type paradox testing scheme, this paperstudies the quantum nonlocal correlation testing of qubit quantum pure state and mixed state in hierarchical environment.Firstly, the physical model of qubit in a hierarchical environment is given, and the evolution of the density matrix of thequantum states in the hierarchical environment is deduced. A highly successful probability testing scheme based on the Hardy-typeparadox for arbitrary quantum states is presented.Secondly, taking the qubit pure state as the object, the quantum nonlocal correlation testing is studied, when the ratio of κ/γ(i.e. the ratio of coupling strength between the quantum pure state and the cavity, and the coupling strength between the cavityand reservoir) is different. At the same time. Also, the in?uence of the quantum pure state on the quantum nonlocal correlationtesting in the evolution of Markovian and non-Markovian environments is given. The results show that with the increase of κ/γ, theevolution time of a successful nonlocal correlation test decreases. In addition, compared with the non-Markovian environment, theevolution of quantum states in the Markovian hierarchical environment is more conducive to maintaining the nonlocal correlationcharacteristics of quantum states.Finally, taking a hidden nonlocal quantum mixed state as the research object, the in?uence of mixing degree parameters andevolution time of the mixed state on the quantum nonlocal correlation testing in the hierarchical environment is studied. The resultsshow that the probability and evolution time of successful quantum nonlocal correlation testing will be signi?cantly reduced withthe decrease of parameter m. When m = 0.849, the lower limit of successful testing will be reached.The results of this paper can provide support for the experimental testing of quantum nonlocal correlation of qubit quantumstates in the hierarchical environment.

In the 90s of the last century, Klyshko proposed an effective field method, based on the advanced wave concept, to describe the basic physical characteristics of spatial correlation for entangled two-photon pairsgenerated in a laser-pumped nonlinear crystal. As a result, the issue of two-photon optics can be understood by conventional one-photon optics. This is a fundamental way to understand one of the laws of nature for mankind. However, the a priori conditionof the advanced wave interpretation requires a basic relationship for the impulse response function of the optical system. Here a theoretical demonstration of the basic relationship is presented and discussed.

The uncertainty principle proposed by Heisenberg is the most basic feature of the area of quantum mechanics, which has been investigated for over ninety-five years with various versions of uncertainty relations obtained, such as the forms of standard deviation and entropy. In recent years, there has been a great interest in quantum-memory-assisted entropic uncertainty relation (QMA-EUR), which has been demonstrated experimentally by now. It is shown that if the measured system and quantum memory are maximally entangled, the measuring outcomes of two incompatible observables can be predicted precisely at the same time. The QMA-EUR has many potential applications in quantum information processing and has been expanded or improved by many scholars. The time-evolving behaviors of QMA-EUR in the open quantum systems have attracted increasing research interest in these years. In particular, the relationships between QMA-EUR and quantum discord, between QMA-EUR and quantum coherence has been discussed widely in the single-layered environment. Moreover, few studies are carried out on the relation between QMA-EUR and quantum dense coding capacity in noisy environments. However, quantum systems can be influenced by the hierarchical environment in realistic scenarios, which has received more and more attention. In this background, we explore in this paper the dynamics of improved QMA-EUR, quantum discord and quantum dense coding capacity in virtue of two identical and independent qubits each immersed in its own hierarchical environment. It is shown that entropic uncertainty and the bound of uncertainty is tight totally in the weak and strong coupling regimes. Meanwhile, entropic uncertainty and the dense coding capacity have a contrary relationship. The coupling strength between the qubit and cavity has an important effect on the evolution of QMA-EUR, the “revival” of quantum discord, and the efficiency of dense coding capacity. Furthermore, we further investigate the manipulation of filtering operation on QMA-EUR, quantum discord and quantum dense coding capacity, and present several significant results.

The measurement of optical power is one of the most important and commonly used measurement techniques in the field of optical research, especially in the field of optical communication, laser mapping and so on. At the same time, the measurement of optical power with better than pW level sensitivity and large dynamic range is a very key technology for system testing and calibration. However, the measurement sensitivity of commercial optical power meters usually can only reach nW level. In this paper, an optical power measuring device with limit sensitivity up to the sparse photon level is developed. The measuring system bases on the silicon avalanche photodiode (Si APD), simultaneously employs the combination of diffuser and electronic diaphragm to achieve precise intensity control of the measured signal light. The accurate optical power measurement in the range of 20fW～300W is achieved, and the response wavelength range of power measurement can cover 530～860nm. The measurement error is proved less than 3.7%, and the relative standard deviation of repeatability is measured less than 1.9%, which can well meet the requirements of the weak optical signal power measurement. This optical power measurement method with both of high sensitivity and large dynamic range is expected to be used in many fields which are facing the difficulty of metering the weak signal in sparse photon level.

Within the framework of the strong-?eld approximation theory, using the quantum S-matrix theory and the saddle pointmethod, we investigated the resonance-like enhancement structures in the high-order above-threshold ionization photoionizationelectron energy spectrum of He atoms, when the ?nal momentum of photoelectrons was aligned along the direction of the stronglaser ?eld and at an angle to the ?eld direction.The research results indicate that the resonance-like enhancement structures appeared regardless of whether the ?nal momentumof photoelectrons was aligned along the polarization direction of the ?eld or at an angle to it, and the intensities of theenhancement peaks also satis?ed the channel closing conditions, further con?rming the channel closing mechanism of resonancelike enhancement. At the same time, it was found that with the increase in laser intensity, the resonance-like enhancement andsuppression phenomena alternated in the photoelectron energy spectrum. When the laser intensity was constant, the resonance-likeenhancement structures gradually shifted towards the low-energy direction as the emission angle of photoelectrons increased. Thesephenomena may be caused by the interference of quantum orbitals with different return times.

The up-conversion and down-conversion process of the second-order nonlinear optical parametric process is a means to expand the laser wavelength range, in which the second harmonic generation and sum frequency generation in the up-conversion process can effectively produce short-wavelength visible lasers with high power and high optical quality. In this paper, an experimental model of injecting the fundamental frequency light field with polarization direction of e and wavelength of 1 438.9 nm into a double-ended optical cavity with a single-period structure (15.69m) is proposed theoretically. The fundamental frequency light passes through the crystal many times, which can improve the conversion efficiency of the output dual-wavelength laser. Class 0 quasi-phase matching with the largest second-order nonlinear polarization tensor is selected. In the same period of the polarized crystal, at the proper working temperature of the crystal, the second-harmonic light field of 719.45 nm and the third-harmonic light field of 479.63 nm can be generated, and the obtained two light fields are output from both ends of the double-ended frequency doubling cavity respectively. The periodic structure of the crystal is designed, and the phase difference caused by the dispersion phenomenon when the interacting light waves propagate in the crystal is well solved by using the quasi-phase matching technology, so that the two nonlinear optical processes corresponding to the second-harmonic light field and the third-harmonic light field meet the first-order quasi-phase matching and third-order quasi-phase matching conditions respectively in the same crystal polarization period. By using the refractive index equation, thermal dispersion coefficient equation and nonlinear optical phase matching condition and other related theories, the relationship between crystal polarization period, fundamental wavelength and temperature is calculated and analyzed. The conclusions obtained can not only provide a theoretical reference value for a single laser to generate dual-wavelength laser in single-period polarized crystal, but also have a certain experimental reference value for further understanding the interaction between laser and atom.

The relative phase of nonlinear waves is a crucial parameter in establishing their structure, properties, and types, as wellas in nonlinear wave interactions. In this paper, we construct the solution of the Kuznetsov-Ma breather, soliton, and the interactionbetween soliton and breather with relative phase on the plane-wave background of the Hirota model. Exploring the relative phaseinduced conversion of Kuznetsov-Ma breather into different solitons, and the relative phase induced soliton state transition duringa breather-soliton collision.First, the study discovered the relative phase does not affect the structure of the Kuznetsov-Ma breather, as demonstrated,because the relative phase of the Kuznetsov-Ma breather changes during evolution. We plot the relative phase variation with z forbreathers of the different initial states. However, altering the relative phase can cause a change in the distribution of solitons andeven the type of solitons, resulting in a diverse range of soliton forms. For example, it is converted from an anti-dark soliton toa non-rational W-shaped soliton. Because solitons usually have constant relative phases independent of the propagation distance.

Correlation is a universal phenomenon of the quantum world. Quantum correlations are used widely in quantum information science, such as quantum coding, quantum key distribution and quantum teleportation. Besides, they play a nonnegligiblerole in quantum communication and information processing. Hitherto, some quantum correlations have been proposed successively.Quantum discord proposed by Ollivier and Zurek is a valuable quantum resource and has wide applications in physical models,quantum calculations, quantum state broadcasting, as well as quantum metrology.However, the quantum system will interact with the environment, and the correlation of the quantum states will be affected bythe environment. This interaction can be described by the quantum noise channel. The study of quantum noise channels is mainlydivided into Markov channels and non-Markov channels, and the difference is whether the memory environment is described.Moreover, a lot of work has been done to make the comparison between quantum discord and entanglement under decoherence.These studies suggest that disentanglement may suddenly occur, when a quantum system with quantum correlations is exposedto a noisy channel, but quantum discord mostly decays over time. This points to the controversial fact that quantum discord maybe stronger than entanglement in opposing decoherence. In a sense, quantum discord is a more general quantum resource thanquantum entanglement, which provides a new development prospect for quantum information processing.The Pauli memory channel is a commonly used channel. The use of each channel in the memory channel is directly orindirectly in?uenced by the previous channel, resulting in correlation effects between the particles. It is found that the correlationeffects in the memory channels can improve the quantum capacity. The Werner states are widely used in quantum protocols, andthese studies all exploit the rich quantum correlations of the Werner states. However, the interference from the environment willaffect the quantum correlation of the Werner states. Therefore, improving the quantum discord of the Werner states under the noisechannel is the goal of improving the information processing ef?ciency.For the Werner state, the in?uence of memory parameter ν on quantum discord is studied in common memory Pauli channels(phase damping, bit ?ipping and depolarization channels). The results show that for Pauli channels without memory (ν = 0), theadvantage of quantum discord gradually disappears with the increase of noise parameter p. In memory channels (ν > 0), quantumdiscord increases with the increase of memory parameter ν. In particular, when the memory parameter ν = 1, the quantum discordreaches its maximum regardless of the noise parameter p. This will help the Werner state resist the decoherence of the environmentin quantum tasks.

Objective In modern production life, there is an important and widespread need to achieve accurate measurement of temperature and relative humidity. Conventional capacitive moisture-sensitive elements lack stability, interactivity and corrosion resistance, and can monitor a small range of humidity. Not only does the characteristic response drift severely in long-term use, but also the accuracy is insufficient to meet the needs of the finishing industry.In contrast, fiber optic sensors have the unique advantages of small size, light weight, anti-electromagnetic interference corrosion resistance, etc. And fiber optic gratings are sensitive to changes in external influences such as temperature and pressure, and are therefore used in large numbers in the sensing field. Based on this, the SPR effect has been widely noticed for its advantage of improving the sensitivity of optical fibers to changes in refractive index of the surrounding environment. In recent years, researchers have developed various temperature and humidity sensors based on the SPR effect and fiber grating using this principle. However, the sensitivity of these sensors needs to be improved, and often cannot achieve simultaneous measurement of temperature and humidity. We propose an SPR-based temperature and humidity sensing structure for single-mode optical fiber grating, which is coated with silver nanofilm after etched cladding, and then coated with a moisture-sensitive film. The structure uses PVA as the moisture-sensitive material combined with SPR effect for humidity detection, and uses fiber grating as the temperature-sensitive device to achieve the measurement of temperature and humidity changes in the surrounding environment.Methods The coated fiber was first removed from the grating side of the fiber with a length of about 10 mm. Then HF acid solution with a concentration of 37.6% was applied dropwise to the surface of the removed fiber, and the corrosion condition was observed several times using an optical microscope until the corrosion cladding diameter was 16m. The treated fiber was fixed on a slide and plated with a silver film of 40 nm thickness by a magnetron sputtering coater. At the end of the silver plating process, the fiber optic sensing structure was flipped to the back side and the plating process was repeated to ensure uniform coating of the entire fiber optic sensing structure. Next, add 0.5 g of PVA powder to a small beaker, add deionized water to a total weight of 10 g, place it on a baking table and heat it to 60℃. Stir while heating until the PVA is completely dissolved, then apply the prepared wet-sensitive solution onto the slide evenly. After submerging the silver-plated part of the fiber in the wet-sensitive solution, the fiber is slowly and steadily lifted out. And as the solvent evaporates, the PVA solution attached to the surface condenses and forms a thin film.Results and Discussions The sensing structure has a good response in temperature and humidity sensing. Both the SPR resonance peak and the central reflection peak were significantly shifted when the temperature and humidity were changed. In thehumidity experiment, Figure 6 shows the resonance peak shift in the transmission spectrum corresponding to the sample under humidity conditions varying from 30%RH to 80%RH. As the humidity increases, the spectral resonance peak shifts unidirectionally toward the short wavelength and the depth of the valley gradually increases. The crosstalk effect of temperature on humidity is shown in Figure 7, and the temperature sensitivity of PVA can be analyzed by linear correction using Formula 4. In the temperature experiment, the fiber grating temperature response, the external temperature increases from 20℃ to 70℃, and the fiber grating center reflection wavelength shift and temperature change is a good linear relationship, as shown in Figure 8. And the experimental results show that the ambient humidity change does not cause a crosstalk effect on temperature detection.Conclusions In this paper, we propose a new fiber grating temperature and humidity sensor based on SPR effect. By cladding etching, the fiber core light is coupled into the cladding, and a 40 nm thickness silver nanofilm is coated outside the cladding, so that the light coupled into the cladding and the silver film excite the SPR effect. The fiber grating is shifted with temperature changes affecting the center reflection wavelength. It has high linearity for temperature measurement, while the silver nanofilm is coated with a moderate thickness of PVA moisture-sensitive film, using the characteristics of the refractive index of the moisture-sensitive film changes with the environmental humidity to achieve the sensor monitoring of environmental humidity changes. The sensitivity reaches 0.020 3nm/℃ when the temperature is in the range of 20℃～70℃ and -0.99nm/%RH when the humidity is in the range of 30%～80%RH. The sensor designed in this experiment can monitor a wide range of humidity variations with high humidity response sensitivity and good stability, and can simultaneously perform temperature parameter measurement, which has a large potential in the field of temperature and humidity sensing

Locking the output frequency of the laser to a suitable reference frequency can effectively improve the frequency stability of the laser, suppress the frequency fluctuation of the laser, and achieve laser frequency stabilization. In this paper, we study the two-color polarization spectroscopy (TCPS) based on the 6S1/2-6P3/2-70S1/2 ladder-type three-level system in a cesium atomic vapor cell at room temperature, and use this TCPS to achieve modulation-free laser frequency stabilization. In the experiment, a linearly polarized 852 nm laser as probe light, resonant at 6S1/2(F=4)→6P3/2(F'=5) transition, a circularly polarized 509 nm laser as coupling light, and laser frequency was scanned near 6P3/2(F'=5)→70S1/2 transition. The circularly polarized coupling light pump atoms live in different Zeeman states to achieve anisotropy in the medium. We obtained the TCPS of the Rydberg state by detecting the anisotropy of the atomic medium by polarized light field, and analyzed it theoretically. And we experimentally measured the dependence of TCPS on the laser power of 852 nm linear polarization probe light and 509 nm circularly polarized coupling light, and the results showed that due to the influence of atomic coherence effect, the linewidth of TCPS was significantly suppressed with the change of coupling power, and due to the influence of optical pumping and power broadening, the coherent effect of the atomic system would be destroyed, and the TCPS linewidth would increase significantly with the increase of probe power. Using this Rydberg state TCPS, we lock the frequency of the 509 nm laser corresponding to the Cesium 6P3/2 (F'=5)→70S1/2 transition, and the frequency fluctuation of the 509 nm laser is significantly improved compared with the frequency fluctuation during free running at the same time. This TCPS provides a modulation-free technique that can be used for frequency locking of laser systems matched to multiple Rydberg states, which is important for precision measurements based on the Rydberg state.

Ultraviolet light has the advantages of large single photon energy, being easily focused, and most materials have strong absorption of ultraviolet light. It is widely used in marking, composite cutting, drilling, fine processing and other fields. An all-solid-state experimental device based on 1 064 nm infrared light and nonlinear optical frequency conversion technology to achieve 10 W 355 nm ultraviolet pulsed laser is reported in this paper. In the experiment, a “Z” type acousto-optic Q-switched 1 064 nm resonator, which is end-pumped by 888 nm semiconductor laser, was designed with a compact structure, stable power and good beam quality. The resonator has a large cavity mode, which can match the pump power well and alleviate the thermal effect of gain crystal. When the pump power is 85.7 W, the maximum average output power of 1 064 nm laser is 33.5 W, and its slope efficiency is 59.8% after linear fitting. The 355 nm ultraviolet laser is obtained by extra-cavity frequency doubling and extra-cavity frequency summing techniques. With the continuous increase of the incident pump power, in addition to the gradual increase of the powers of the 1 064 nm laser, 532 nm laser and 355 nm laser, the beam waist sizes and positions of the 1 064 nm laser and the 532 nm laser at the sum frequency crystal will have small changes, which will directly affect the output power and conversion efficiency of the 355 nm ultraviolet laser. When the incident pump power and repetition rate are 80 W and 50 kHz, respectively, a pulsed 355 nm ultraviolet laser with an average output power of 10 W, beam quality of M2x=1.12 and M2y=1.03 is obtained, and the conversion efficiency from the pump light to the ultraviolet light is 12.5%. It can be predicted that further optimizing the power ratio and beam waist size on this basis will result in a larger output power of 355 nm ultraviolet light.

This study provides a novel and effective way to fabricate perovskite-based saturable absorbers with enhanced stability and optical performance for Q-switched laser applications. Perovskite materials have become a hot topic in recent years because of their unique crystal structure, tunable direct band gap and broadband saturable absorption. The purpose of this paper is to investigate the feasibility and performance of perovskite-based saturable absorbers based onanodic alumina films for Q-switched laser applications.In this paper, perovskite-based (CH3NH3PbI3)/anodic alumina (AAO) saturable absorbers were prepared by a limited domain growth method. The existence of AAO films not only improved the stability of CH3NH3PbI3 in air, but also improved the optical properties of the saturable absorbers (SA). The modulation depth of CH3NH3PbI3AAO-SA was about 7.2%, and the saturation light intensity was about 9.65MW/cm2. By inserting CH3NH3PbI3AAO-SA into the resonator of Nd:YVO4 all-solid-state passive Q-switched laser, a stable Q-switched pulse with a center wavelength of 1 064.07 nm was obtained. When the pumping power was 7 W, the minimum duration of the laser output pulse was about 360 ns, and the average output power was 483 mW. At this time, the pulse repetition rate was 446 kHz, and the radio frequency (RF) spectrum signal-to-noise ratio (SNR) was 44 dB.Compared with previous studies, the perovskite-based saturable absorbers in this paper achieved a higher saturation intensity, a shorter pulse width and a lower SNR, demonstrating their superior performance for Q-switched laser applications.