A new design of planar mirror multipass cell (MPC) is proposed. In this scheme, the new MPC consists of two low-cost silver (or gold)-coated plane mirrors and two biconvex lenses, so compared with the traditional expensive concave mirror and cylindrical mirror MPCs, which is more economical and applicable. In the new MPC, the outer side of the plane mirror is coated with high reflectivity silver or gold film. This coating method insulates the reflective coating of the plane mirror from the corrosive target gas, reduces the pollution of the corrosive gas to the protective silver (or gold) layer of the plane mirror, so as to improve the service life and detection accuracy of the instrument. In order to verify whether the new optical multipass cell has the capability to provide an effective long optical path, the optical simulation of three new optical MPCs with different design parameters is carried out by using optical software. Compared with the traditional White cell and Herriot cell (about 700 cm3 in volume, with about 80 times reflections), the simulation resultsshow that 62, 100, 99 times of light reflections and the effective optical path of 14.64, 40, 42.57 m can be achieved in a small volume (about 236, 393, 422 cm3). The ratio of the effective optical path to the volume of the multipass cell is 100, 62 and 101 mm－2 respectively, which indicates that the space utilization of the new optical MPC is very high. It is shown that this new type of optical MPC has the advantages of small volume, long optical range, low cost and high sensitivity, which is expected to be used in environmental monitoring, combustion process analysis, medical diagnosis and other fields due to the high detection sensitivity to trace gases.

Phase error correction is one of the key steps in generating high quality spectrum. The commonly used Mertz method that recovers the spectrum from zero-crossing sampled single-sided interferogram data can correct the phase error efficiently. However, this method do not uniformly utilize the asymmetric interferogram data, which causes theinaccuracy of high frequency components in the spectrogram. To address this problem, an improved Mertz-based phase correction method is proposed by weighting asymmetric interferogram with an odd polynomial. The improved Mertz method can utilize the spectral information of small bilateral interferograms uniformly. Extensive experiments demonstrate that the proposed method can effectively recover the spectral details and improve the spectral signal-to-noise ratio. Compared with the method using linear weighting function, the proposed odd polynomial increases the average peak-to-peak signal-to-noise ratio by 1.2% and 2.3%, and improves the root mean square signal-to-noise ratio by 3.6% and 1.1% in 900～1100 cm－1 and 2500～2600 cm－1 bands, respectively.

Exciton properties have a decisive influence in the luminescence mechanism of quasi-2D perovskite material. Measurement of exciton-phonon coupling strength and exciton binding energy is a powerful means of investigating exciton properties of quasi-two-dimensional perovskite materials, which can provide a key scientific basis for revealing the internal light emission mechanism and further improving the fluorescence quantum yield. By combining the adjustable pump intensity fluorescence testing system with the liquid nitrogen thermostat, a set of variable temperature fluorescence test system with adjustable pump intensity is built and controlled by the LABVIEW program. Then the exciton and luminescence properties of quasi two-dimensional perovskite film samples are studied by using the built system. The experimental results show that the exciton-longitudinal optical phonon coupling strength and exciton binding energy decrease with the increase of n-value of quasi-two-dimensional perovskite. In addition, by measuring the adjustable pump intensity fluorescence at room temperature with the built system, the optical gain of quasi-two-dimensional perovskite films is explored, and it is shown that the amplified threshold of spontaneous emission of the film is 3.2 μJ/cm2.

To develop useful superconducting quantum systems, the quality of qubits needs to be improved furthermore. At present, defects in materials and their interfaces are important factors affecting the coherence time of qubits. As an important part of superconducting quantum chip, microwave resonator can be used to characterize the quality of materials and the fabrication process of devices. Using molecular beam epitaxy technology, aluminum is deposited on intrinsic silicon (111) substrate to prepare the λ/4 coplanar waveguide resonators. By the preparation of silicon substrate and the deposition of high quality aluminum films, the intrinsic qualityfactor of the resonator is improved to 106 at 20 mK with the probing power at near single-photon level.

B-spline function is used to solve numerically the energy eigenvalue of electrons in hydrogen atom under the interference of random potential field. The eigen energy and eigen wave function of electrons in hydrogen atom in the case of random potential with different amplitude range are calculated. The results show that the probability of electron distribution changes more frequently when the range of stochastic potential is larger. And the more quantumnumbers there are, the more unstable the system becomes, and the more easily the central force field is destroyed by the applied stochastic potential field.

The dynamical evolution of quantum entanglement and quantum coherence of two atoms in an extended Werner-like state coupled with two independent zero temperature vacuum reservoirs is studied. It is found that the quantum entanglement and quantum coherenceof two atoms are affected by the initial state and purity, and the quantum entanglement and quantum coherence of each subsystem can transfer to each other and satisfy the corresponding conservation equations. It is shown that the initial Bell-like state and purity determine the conservation equations of quantum entanglement and quantum coherence, and for the same Bell-like state, the conservation of quantum entanglement and quantum coherence is not affected by Markovian or non-Markovian environment.

Experimental investigation of parametric coupling of two vibration modes in a two-coupled-cantilever-based mechanical system is carried out, and the influence of mode frequency difference on coupling strength is investigated. In the experiment, a tunable two-mode system is constructed by trapping one of the cantilevers optically, and the parametric coupling between the two modes is realized by applying a parametric drive through periodically modulating the trapping power. Furthermore, the parametric coupling under distinct frequency differences between two modes is studied and the relationship between coupling strength and frequency difference is obtained experimentally. The result is beneficial to realizing the accuracy control of the coupling strength of two modes under distinct frequency differences.

Information reconciliation is an important part of a continuous-variable quantum key distribution (CV-QKD) system. Polar code is applied to multidimensional reconciliation protocols for CV-QKD, and twonew polar code multidimensional reconciliation protocols are proposed in this work. The new protocol consists of the multidimensional algorithm part and error correction part. In the first part, the long sifted key can be divided into a set of d-dimension vectors, and then each group of vectors can be transformed to a binary data after normalization, spheroidization and rotation. In the second part, the communication parties can share the frozen position information and frozen bit value, and realize the reverse information reconciliation based on the polar code. The simulation results show that compared with the original inverse polar code reconciliationprotocol, the proposed protocol can achieve higher negotiation efficiency while the error correction success rate remains unchanged.

Aiming at the market demand of quantum key distribution (QKD) technology, a random number source implementation scheme and high-speed self-check algorithm for QKD products are proposed. Commercial WNG-8 noise source chip is used to build chip array as the random number source in the system, and the reliability of random number is improved by means of XOR process. According to relevant national standards, a high-speed Poker self-check algorithm scheme is designed based on FPGA. By optimizing the decision strategy, implementing the Ping-Pong switching control and parallel statistics of the random data flow, the processing bandwidth of 3.8 Gbps is realized, which could be further improved to 10 Gbps to meet the real-time checking requirement for future high speed QKD products.

Fast and efficient privacy amplification plays an important role in high throughput quantum key distribution (QKD) system. In general, implementation of privacy amplification relies on large integer multiplication, binary matrix multiplication or polynomial multiplication over finite field. Especially, privacy amplification based on polynomial multiplication has the advantage of low requirement on random number, while has relatively high implementation complexity. In this work, Toom-3 algorithm over finite field with four elements is developed and the corresponding explicit formula is derived, then a new privacy amplification method based on Toom-3 algorithm is presented. The time complexity of the method is O(n1.465), which indicates that the method is suitable for parallel computing and hardware implementaiton.

To solve the problem of information leakage of pulse width and frequency possibly caused by pulse intensity modulation in current active decoy-state quantum digital signature scheme, a passive decoy-state quantum digital signature scheme based on linear optical components is proposed. In this scheme, decoy states are passively constructed to estimate channel parameters by making two weak coherent sources to pass a beam splitter and trigger the local detector, so that the research of quantum digital signature can be carried out. This passive decoy-state quantum digital signature scheme can not only avoid the side channel vulnerabilities caused by active pulse intensity modulation and improve the security of the system, but also weaken the effect of modulation error and intensity fluctuation generated in the preparation process of the active decoy-state scheme.

Based on the theory of non-Kolmogorov atmospheric turbulence spectrum, a mathematical model of spatial two-qubit entangled states propagation in non-Kolmogorov atmospheric turbulence is established, the corresponding mathematical expression of entanglement degradation is obtained, and the influence of non-Kolmogorov turbulence on the entanglement of spatial two-qubit states is analyzed by numerical simulation. The results show that high entanglement of the spatial two-qubit entangled states can be maintained when the physical size and separation between each signal and the corresponding idler apertures is small. Moreover, it is found that when the long wavelength entangled photons propagate through non-Kolmogorov atmospheric turbulence with larger generalized refractive-index exponent parameter α and generalized refractive-index structure parameter C~2n, the entanglement degradation is relatively weak. The proposed model can be used to quantitatively analyze the entanglement degradation, which is helpful for long distance self-adaption quantum communication with low bit error rate.

Non-equilibrium environment is one of the most common dissipative factors encountered in the application of quantum system. The dynamic evolution and steady-state solutions of two coupled qubits in both equilibrium and non-equilibrium environments are studied systematically. The results show that in the equilibrium bath, enhancing the coupling strength, increasing the energy detuning and raising the temperature of the heat bath are all beneficial to the enhancement of the entanglement. While in the non-equilibrium bath, the entanglement is enhanced (suppressed) with the increasing of the temperature gradient for the low (high) average temperature. In addition, the relationship between the heat current and the energy detuning, the coupling strength and thetemperature of bath is also studied. It is found that for the two qubits in two independent heat baths or in two common heat baths, the influence of parameters on the evolution of the system and the heat current is different. By selecting appropriate coupling strength, energy detuning and temperature gradient, the stable heat current between two heat baths can be obtained, so the steady-state entanglement of the system.

The universal mathematical models of memristor, meminductor and memcapacitor are designed respectively, and based on these models, a simple parallel chaotic system is constructed. The dynamic characteristics of the system including phase diagram, time domain diagram, Lyapunov index, power spectrum and poincare cross section are analyzed, and its hyperchaotic characteristics are proved. The influence of equilibrium point stability, system parameters and initial value on the system is further studied. And it is shown that the symmetry change of parameters will cause the corresponding symmetry change of system state, however, the initial value does not affect the state of the system under the condition of chaotic oscillation. Finally, the circuit is designed and realized by using Multisim, and the numerical simulation results are in good agreement with the experimental results, which proves the practical feasibility and actual existence of the system. This work not only extends the application of memory element in the nonlinear category, but also makes the basic work for the practical application of memory element based hyperchaotic system.

In order to enhance the intensity of high order harmonic spectrum, a method of improving harmonic intensity by using resonance ionization is proposed. The results show that, in case of He atom system, the harmonic intensity can be enhanced by 50 times under the influence of ultraviolet resonance ionization. Moreover, with the introduction of chirped pulse, the harmonic cutoff can also be extended, showing an intense and broad harmonic plateau. In case of H+2 molecule system, the harmonic intensity canbe enhanced by nearly 20 times under the influence of charge resonance enhanced ionization. And with the optimization of the half-cycle unipolar pulse, the extension of harmonic cutoff for H+2 molecule system can also be achieved, showing a harmonic plateau contributed by single harmonic emission peak. The further study shows that by superposing some harmonics on the harmonic plateaus, the attosecond pulses with durations of 36 as and 32 as can be obtained for the two systems, respectively. It is confirmed that the proposed scheme is helpful to enhance the intensity of attosecond pulse.

The effect of magnetic field (MF) on the ground state energy of weak coupling polarons in monolayer transition metal dichalcogenides (TMDs) is studied by using LLP unitary transformation and linear combination operator. The dependence of the ground stateenergy of weak coupling polarons on MF, Debye cutoff wave number (DW), internal distance and intrinsic polarizability parameters of the phonon in MF is obtained. The numerical calculation results show that the ground state energy of the weak coupling polarons increases with the increase of magnetic field and the intrinsic polarizability parameter, and decreases with the increase of DW and internal distance of the phonon.