Quantum communication is an innovative method of transmitting information that utilizes quantum states. It encompasses research areas such as quantum key distribution and quantum secure direct communication. By harnessing the properties of quantum mechanics, quantum communication enables theoretically absolute secure transmission that is immune to eavesdropping or decryption through computational means. The terahertz band, well-known for its high frequency and wide bandwidth capabilities, has emerged as the preferred frequency range for 6th Generation (6G) wireless communication. Therefore, the combination of terahertz communication with quantum communication holds great potential for enhancing secure communication in the era of 6G. This article offers a comprehensive overview of the advancements in terahertz quantum communication for the first time, with a specific focus on the latest research progress of terahertz quantum key distribution in terrestrial atmospheric environments and inter-satellite link.

A highly sensitive transient absorption spectrometer was developed in this work using a nanosecond pulse diode laser as a pump source, and rapid and high sensitivity transient absorption(∆A<5×10-6) was achieved by using the balanced detection, the timing structure of macro-pulse andmicro-pulse and an electronic delay scheme to avoid repetitive balancing. Then, the carrier dynamics of methylammonium lead iodide (MAPbI3) thin film perovskite materials at different pump power densities were measured using the developed spectrometer, and pump power density-dependent dynamic phenomena were observed. Especially, the measurement of carrier dynamics in the linear response region was achieved at low carrier concentrations. Furthermore, the carrier dynamics of MAPbI3 at 296 K and 220 K were measured and compared, and it was found that the carrier lifetime was extended at low temperature due to the reduction of charge recombination assisted by ionization impurities. The highly sensitive transient absorption method proposed in this work can be extended to full nanosecond pulse diode laser systems, which will not only reduce the cost of transient absorption spectrometers but also have the potential applications in rapidly evaluating the intrinsic properties of materials at low carrier densities under solar illumination.

Underground coal gasification is an important way to realize clean and efficient utilization of coal. In order to realize the detection of methane produced by underground coal gasification, a wide-spectrum measurement technique based on tunable diode laser absorption spectroscopy (TDLAS) for methane at high temperature and high pressure and the corresponding gas parameter inversion method are proposed in this work. Firstly, a wide-spectrum measurement system for high temperature and high pressure methane was established based on a tunable semiconductor laser with a wide wavelength tuning range. Then, the absorption spectrum of 2.05% standard methane gas was measured using the system at temperatures of 200 oC and 400 oC and pressures of 0.5 × 106–3.0 × 106 Pa, with spectral wavenumber ranging from 6010–6190 cm-1. Finally, based on absorption spectroscopy, simultaneous inversion of multiple parameters including methane concentration, temperature and pressure were achieved using the least squares fitting algorithm, and the inversion errors of each parameter were all within 10%. The research provides an effective and feasible means for on-line detection of methane gas produced by underground coal gasification.

The combustion process of hydrocarbon fuel will produce a lot of carbon smoke. C2H2, as an important precursor of carbon smoke products, has an important effect on carbon smoke generation, so it is of great significance to achieve direct detection of C2H2 in combustion environment. In this work, a tunable diode laser absorption spectroscopy system was established to detect C2H2 gas absorption spectra at different temperatures and pressures by simulating combustion environment in a high temperature and high pressure gas pool. Specifically, taking a tunable semiconductor laser with a central wavelength of 1542 nm as the light source, the absorption line extinction signals of acetylene at 6489.074 cm-1 and6490.020 cm-1 were obtained using the scanning wavelength direct absorption method, thereby achieving simultaneous measurement of C2H2 concentration and temperature. The experimental results show that, in the pressure range of 1.01 × 105–5.05 × 105 Pa and temperature range of 500–1100 K, the relative average standard deviations of gas volume concentration and gas temperature measurement are 4.59% and 2.47% respectively, which are in high agreement with the reference values. It proves that the developed system in this work can provide assistance for simultaneous measurement of gas concentration and temperature under high temperature and high pressures.

Based on the linear response theory, the frequency and charge distributions of the plasmons in double Au atomic chain systems were studied using energy absorption spectroscopy. The results show that, in the case of the same chain length, the plasmon modes in double Au atomic chain are more prone to coupling with each other than those in single atomic chain, manifested as a single broad energy absorption peak in the single-chain system splitting into multiple sharp peaks in the double chain system, and the coupled plasmon modes exhibit opposite charge polarization directions. Furthermore, whether it is dipole or quadrupole plasmon, the frequency of the strongest energy absorption peak in double atomic chain is higher than that in single chain. The size effect of plasmons caused the frequencies of plasmons with the same order in a double chain system is lower than those in a single chain system, and in the low frequency range, there are more plasmon modes in a double chain system than in a single chain system.

To address the morphological processing problem of images on quantum computers, several morphological processing methods for quantum images were studied. Firstly, an improved quantum representation method for images with any size was proposed. In the method, both pixel value and pixel position were represented by quantum basis state, and the number of quantum basis states representing pixel positions was equal to the number of pixels. Then, by designing quantum circuits for the two basic operations of dilation and erosion, several quantum morphological processing methods for binary images were designed, including noise removal, boundary extraction, and skeleton extraction. Finally, the implementation effect of the designed methods was verified through simulation on classical computer, and the complexity of quantum circuits was analyzed based on the number of basic quantum gates used. The results show that the methods proposed in this work can achieve speedup over classical methods.

In response to the challenge that complicated control fields are generally required for realizing the high-performance shortcuts to adiabaticity quantum Otto cycle (QOC), the performance characteristics of QOC under linear driving field which is easy to manipulate in experiment, are studied in this work. Using the strategy-based deep reinforcement learning, the driving field added during the expansion and compression processes of QOC with single qubit as the working medium is optimized, and then the high-performance QOC under linear driving field can be realized. Compared with the scheme of QOC with the non-adiabatic free evolution, the QOC under the optimized additional driving scheme exhibits significant advantages in the output work, power and efficiency. Especially, in the case of short-cycle period, for the QOC under free evolution scheme, the output of positive work is completely suppressed due to the generation of a large amount of irreversible work, while the QOC under the optimized driving scheme can still operate normally (with output positive work). This work preliminarily tests the validity of deep reinforcement learning in optimizing the performance of quantum engine.

In mode-locked fiber laser, pump coupling, spectral filtering and polarization dependent isolation loss were simultaneously obtained based on highly integrated fiber component, so as to achieve self-similar passive mode-locked pulses at 1550 nm. At the same time, an all-fiber amplifier was also built for nonlinear gain management amplification, so that the self-similar pulses with 10 dB spectral width of 25.9 nm were successfully amplified and broadened to 52.6 nm, and then compressed to 66 fs by anomalous dispersion fiber. Finally, numerical simulations based on the generalized nonlinear Schr?dinger equation and the laser rate equation were carried out to explore the pulses operation process in mode locked fiber laser and fiber amplifier theoretically. The simulation results show that narrow band filter inside the cavity and long normal dispersion gain fiber are necessary conditions for the generation of linearly chirped self-similar mode-locked pulses. And after pre-compression by fiber, self-similar amplification and nonlinear gain-managed amplification of the pulses can be achieved simultaneously with sufficiently long normal dispersion gain fiber, thereby outputting mode-locked pulses with duration less than 100 fs in all-fiber structure.

The moon has the advantages of high stability, gentle variation of reflectance spectra, low background influence, and being free from atmospheric effects when used for satellite in-orbit radiation calibration. As lunar radiation is affected by factors such as lunar phase angle, lunar alignment, and distance between the sun and the moon, lunar calibration necessitates long-term ground-based observation to establish a high-precision lunar radiation model. Therefore, an automatic tracking system for the ground-based lunar spectral irradiance meter was designed in this paper. The preliminary tracking for the system is achieved by calculating the zenith and azimuth angles of the moon using the lunar position algorithm, and then precise tracking is accomplished through image processing of the lunar images captured by a CCD camera. The outdoor tracking observation experiments show that, the tracking approach combining lunar position calculation and image processing tracking possesses relatively high precision, with an average tracking accuracy within 0.04°, validating the high accuracy and reliability of the lunar tracking system.

The realization of photon-photon quantum teleportation based on cavity optomechanical system has made important progress. Nevertheless, transmitting the photon's quantum state that are convenient for transmission to phonon with long lifetime via quantum teleportation is still an challenging issue that awaits resolution. Based on the hybrid cavity optomechanical system, a physical implementation scheme for the nonlocal transmission of unknown quantum states solid-state qubits and flying qubits through nonlinear interaction is proposed. In order to explore the feasibility of the scheme, the influence of temperature and cavity dissipation on the fidelity of hybrid quantum teleportation between phonon and photon is considered. The results show that high-fidelity hybrid quantum teleportation between phonon and photon can be realized by adjusting appropriate parameters under certain temperature and dissipation conditions, which has high theoretical significance in non-local hybrid quantum information processing.

As an important step in the post-processing part of quantum communication, the privacy amplification process can realize unconditional security of quantum key distribution (QKD) system by eliminating information leakage that may occur in the process of QKD. To reduce the consumption of hardware resources and improve the bandwidth of secure key rate, a high-speed privacy amplification algorithm based on cellular automata is implemented in this work using field programmable gate arrays (FPGA). Compared to the Toeplitz matrix scheme that requires huge matrix multiplication, this scheme has greater advantages in speed by improving the algorithm in line with the characteristics of FPGA hardware and pipeline structure. In the case of real-time transmission of reconciliation keys, this scheme can adapt to any length of input keys and any fractional compression ratio between 0 and 1. In addition, the 256-order cellular automata is used in this scheme to process 1.28 Mbits input keys, and the maximum bandwidth of secure key rate can reach 1540 Mbits/s at a compression ratio of 0.5.

Yb3+ doped (atomic number fraction of 5%) gadolinium-sodium-potassium molybdate laser crystal K0.1Na0.9Gd(MoO4)2 was grown by Czochralski method in this work. Then the crystal structure was characterized and the density, specific heat, thermal diffusivity and thermal conductivity were measured. Additionally, a simple and effective theoretical fitting method for specific heat and thermal diffusivity was proposed, and the fitting results were in good agreement with the experimental results. The results have shown that, the crystal belongs to tetragonal crystal system, with the structural characteristics of scheelite, the experimental density and theoretical density are 5.3792 g/cm3 and 5.3460 g/cm3, respectively, the Vickers hardness of the crystal along the b-axis is 251.5 kg/mm2, and as the temperature increases, the thermal conductivity of the crystal decreases from 1.03 W⋅m-1⋅K-1 at 300 K to 0.91 W⋅m-1⋅K-1 at 400 K. The specific heat of the crystal at 300 K is about 0.62 J·g-1·K-1, indicating that the crystal has a high thermal damage threshold. Under the excitation of InGaAs laser diode with the wavelength of 970 nm, the strongest emission peak of the crystal appears at 1023 nm with bandwidth of 43 nm, indicating that the crystal is promising for broadband tunable and ultrashort pulse laser. The study of the mechanical, thermodynamic, and spectral properties of the crystal can provide an important reference for the study of its laser performance.

Aiming at the lack of adaptive target selection strategy for parameterized quantum circuits in current quantum convolutional neural network models, a quantum convolutional neural network model based on the particle swarm optimization algorithm is proposed to optimize circuits automatically. The model optimizes quantum circuits by encoding the quantum circuits as particles, then uses the particle swarm optimization algorithm to search for the circuit architectures that performs well in image classification tasks. Stimulation experiments based on Fashion MNIST and MNIST datasets show that the model has strong learning ability and good generalization performance, with accuracy up to 94.7% and 99.05%, respectively. Compared to current quantum convolutional neural network models, the average classification accuracy is improved by 4.14% and 1.43% to the maximum, respectively.

In the noisy intermediate scale quantum (NISQ) era, the restricted connectivity of qubits in quantum chip makes direct execution of dual quantum gates in quantum circuits impossible. Therefore, it is of great significance to map logical quantum circuits onto quantum chips and make double quantum gates directly executable. This paper proposes a quantum circuit mapping method based on dynamic division of circuits and recombination of gate sequences, and conducts an equivalence verification of swapping rules based on ZX-calculus. The method divides the circuit into three layers dynamically, sets a moving window behind the reference gate during the mapping process, and adopts a left-greedy movement method to reorganize the gate sequence through the exchange rules, thereby reducing the number of additional gates in the mapping process. Experimental results show that, compared with existing mapping methods, the method proposed in this work requires fewer additional gates, with an average optimization rate of 24% and a maximum optimization rate of 46%.