Field test of quantum key distribution over aerial fiber based on simple and stable modulation.

We have developed a simple time-bin phase encoding quantum key distribution system, using the optical injection locking technique. This setup incorporates both the merits of simplicity and stability in encoding, and immunity to channel disturbance. We have demonstrated the field implementation of quantum key distribution over long-distance deployed aerial fiber automatically. During the 70-day field test, we achieved approximately a 1.0 kbps secure key rate with stable performance. Our work takes an important step toward widespread implementation of QKD systems in diverse and complex real-life scenarios.

Time-bin phase-encoding quantum key distribution using Sagnac-based optics and compatible electronics.

In this work, we present a new time-bin phase-encoding quantum key distribution (QKD), where the transmitter utilizes an inherently stable Sagnac-type interferometer, and has comparable electrical requirements to existing polarization or phase encoding schemes. This approach does not require intensity calibration and is insensitive to environmental disturbances, making it both flexible and high-performing. We conducted experiments with a compact QKD system to demonstrate the stability and secure key rate performance of the presented scheme. The results show a typical secure key rate of 6.2 kbps@20 dB and 0.4 kbps@30 dB with channel loss emulated by variable optical attenuators. A continuous test of 120-km fiber spool shows a stable quantum bit error rate of the time-bin basis within 0.4%∼0.6% over a consecutive 9-day period without any adjustment. This intrinsically stable and compatible scheme of time-bin phase encoding is extensively applicable in various QKD experiments, including BB84 and measurement-device-independent QKD.

Effect of hydrostatic pressure on the structural, elastic, and optoelectronic properties of vacancy-ordered double perovskite Cs2PdBr6.

The vacancy-ordered double perovskite Cs2PdBr6 has the advantages of good optoelectronic properties, environmental friendliness, and high stability. It has been experimentally confirmed by researchers as an optoelectronic material with broad application prospects and research value, and is regarded as a potential substitute for lead halide perovskites. In this paper, based on the first-principles calculations in the framework of density functional theory, the crystal structure, elastic, electronic, and optical properties of Cs2PdBr6 under hydrostatic pressure of 0-6 GPa have been investigated with a step size of 0.5 GPa. The calculated results obtained under the condition of 0 GPa hydrostatic pressure are in good agreement with the existing experimental values. When the hydrostatic pressure is applied, the crystal structure parameters of Cs2PdBr6 appear nonlinear changes, but it can still maintain a stable cubic crystal structure. With the increase of pressure, the bulk modulus, shear modulus, and Young's modulus of Cs2PdBr6 increase gradually, and its ductility also improves gradually. Hydrostatic pressure can reduce the bandgap value of Cs2PdBr6, thereby enhancing the optoelectronic properties such as absorption and conductivity. In summary, hydrostatic pressure can change the bandgap value of Cs2PdBr6, improve its optoelectronic performance, and make it more suitable for use as the light-absorbing layer in solar cells.

Theoretical exploration of mechanical, electronic structure and optical properties of aluminium based double halide perovskite.

The mechanical, electronic structure and optical properties of aluminium based double halide perovskite were calculated by density functional theory. The formation energy and elastic constant confirm the stability of the cubic perovskite materials. The materials are all ductile and suitable for flexible photovoltaic and optoelectronic devices. The band gap values vary from 0.773 eV to 3.430 eV, exactly corresponding to the range of ideal band gap values for good photoresponse. The band structure analysis shows that all the materials possess small effective mass, which indicates a good transport of carriers. And these materials have a broad energy range of optical absorption for utilization and a detector of photons. Moreover, less expensive K2AgAlBr6 were investigated for comparison with materials containing a cesium element, and according to the results, is also a candidate for photoelectronic devices due to the similar properties.

Theoretical Study on the Carrier Mobility and Optical Properties of CsPbI3 by DFT.

The advantages of organic-inorganic hybrid halide perovskites and related materials, such as high absorption coefficient, appropriate band gap, excellent carrier mobility, and long carrier life, provide the possibility for the preparation of low-cost and high-efficiency solar cell materials. Among the inorganic materials, CsPbI3 is paid more attention to by researchers as CsPbI3 has incomparable advantages. In this paper, based on density functional theory (DFT), we first analyze the crystal structure, electronic properties, and work function of two common bulk structures of CsPbI3 and their slices, and then, we study the carrier mobility, exciton binding energy, and light absorption coefficient. Considering that CsPbI3 contains heavy elements, the spin-orbit coupling (SOC) effect was also considered in the calculation. The highest mobility is that electrons of the cubic structure reach 1399 cm2 V-1 S-1 after considering the SOC effect, which is equal to that of traditional solar cells (such as Si-based, PbSe, and PbTe). The lowest exciton binding energy is 101 meV in the cubic bulk structure, which is beneficial to the separation of photogenerated carriers. In the visible region, the absorption coefficient of the cubic structure is the best among all structures, reaching 105 cm-1. Through the study of mobility, exciton binding energy, and light absorption coefficient, it is found that the cubic bulk structure in all structures of CsPbI3 has the best photoelectric performance. This paper can provide some guidance for the experimental preparation of CsPbI3 as a potential high-efficiency solar cell material.

Long-distance transmission of quantum key distribution coexisting with classical optical communication over a weakly-coupled few-mode fiber.

Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber using wavelength-division multiplexing, given the same fiber-input power, the Raman noise in FMF using the mode-wavelength dual multiplexing is reduced by 86% in average. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks.

Study on the properties of perovskite materials under light and different temperatures and electric fields based on DFT.

The photoelectric conversion efficiency of perovskite solar cells has improved rapidly, but their stability is poor, which is an important factor that restricts their commercial production. This paper studies the physical and chemical stability of perovskite solar cells based on first principles. It is well known that methylamido lead iodide compounds and methylamino lead iodide compounds are easily degraded into NH2CH[double bond, length as m-dash]NH2I, CH3NH3I and PbI2. First, the chemical stability of the above two perovskite-type solar cell materials is discussed by calculating the binding energy. Then, their phonon scattering lines, state density and thermodynamic properties are calculated and analyzed, and the work functions of different types of crystals along different planes such as [1 0 0], [0 1 0 0], [0 0 1] and [1 1 1] are calculated. The results show that the work function of the methylamine iodized lead compound is greater than that of the methylamidine iodized lead compound, which means that the electrons of the methylamidine iodized lead compound escape more easily and the carrier transfer efficiency is higher under the same conditions. Finally, the effects of different temperatures, different electric fields and light on the two kinds of crystal materials are analyzed. This provides theoretical guidance for us to improve the stability of perovskite materials experimentally.

Study on the Property of Electron-Transport Layer in the Doped Formamidinium Lead Iodide Perovskite Based on DFT.

The electron-transport layer in planar perovskite solar cells plays an important role in improving photoelectric conversion efficiency. At present, the main electronic transmission materials in perovskite solar cells include TiO2, ZnO, WO3, ZrO2, SnO2, ZnO2, etc. This work mainly studies the electron-transport characteristics of six different electron-transport layers in perovskite solar cells. Based on the density functional theory, the electron-transport model of a solar cell doped with formamidinium iodide lead compound perovskite under six different electron-transport materials was constructed, and their effective electron mass and the mobility of carriers were obtained by optimizing the structure and theoretical calculation. The results show that the mobility of electrons in TiO2 crystal is slightly higher than that of FA0.75Cs0.25Sn0.5Pb0.5I3 carriers. Because of their high matching degree, it can be reasonably explained that titanium dioxide has been widely used in perovskite solar cells and achieved higher photoelectric conversion efficiency. In addition, the mobility of carriers in WO3 and SnO2 crystals is also high, so they also have great advantages in carrier transport. Due to its abundant, nontoxic, and low-pollution content, TiO2 has become the most widely used electronic transmission layer material for solar cells. Furthermore, we have explored eight new semiconductor materials that have not yet been used in perovskite solar cells as the electron-transport layer. The calculation results show that Ta2O5 and Bi2O3 are promising materials for the electron-transport layer. This study provides a theoretical basis for seeking better electronic transmission materials for solar cells in the future.

[Study on the frontier orbital and Raman spectra of Aflatoxin B1 and isomer].

Through computation, this paper obtained Aflatoxin B1 and its trans-isomer molecules stable structure which was rarely reported by the density functional theory(DFT) with B3LYP complex function and 6-311 + g(d, p) basis set. Through a single point calculations and geometry analysis, we know that the cis-structure is more stable than trans-structure. On the basis of this, Raman spectra of two molecules are calculated by the same method and basis set. compared with the Aflatoxin B1 cis-structure powder experimental Raman spectra, it was informed that numerical results with experimental results combined with a better. While 1582, 3065, 1626 means to take the strongest of the three peaks of cis-structure raman characteristics, 1616, 3065, 1659 cm(-1) is indicated for the strongest of the three peaks of trans-structure raman characteristics. Use the Hirshfeld atom division method combined with Multiwfn software to analyze the composition of frontier orbital based on optimization calculation, and it was informed that the electrophilic ability of two monlecules was stronger than the nucleophilic ability. The proportion of C1 atoms in LUMO orbital are respectively 21.48 percent, 20.62 percent by calculating, thus it is predicted that C1 atom is most main position spot depriving of the electronic in DNA to cause cancer. The above-mentioned research has certain theoretical directive significance in detection, transformation and toxicity inhibition of the cis-trans isomers.

Measurement-device-independent quantum key distribution over 200 km.

Measurement-device-independent quantum key distribution (MDIQKD) protocol is immune to all attacks on detection and guarantees the information-theoretical security even with imperfect single-photon detectors. Recently, several proof-of-principle demonstrations of MDIQKD have been achieved. Those experiments, although novel, are implemented through limited distance with a key rate less than 0.1 bit/s. Here, by developing a 75 MHz clock rate fully automatic and highly stable system and superconducting nanowire single-photon detectors with detection efficiencies of more than 40%, we extend the secure transmission distance of MDIQKD to 200 km and achieve a secure key rate 3 orders of magnitude higher. These results pave the way towards a quantum network with measurement-device-independent security.

[The self intensification of the pure spectrum in the mixed spectrum].

In the present paper, the influence of the pure spectrum contained in the mixed spectrum was centralized at the origin, and in this way, the influence of the pure spectrum in the result curve reached the maximum value. This process is called the self intensification of the pure spectrum. Farther, considering that the center of the Gaussian function contained in the impure spectrum is much different from that of the pure spectrum, it can be accepted that the influence of the impure spectrum at the origin is approximately the minimum. So the origin was chosen as the analysis point when the authors perform the quantitative analysis according to the spectrum. Therefore we can reduce the subjectivity in choosing the analysis point. In addition, the wavelet coefficients of the result curve at the origin were used for the quantitative analysis. According to the simulated experiment, it was found that the final result is independent of the Gaussian white noise contained in the actual spectrum. Finally, the analytic result of the new method was compared with that of the method reported in the literature, which proved that the new method is much better in terms of the analytic error.

[Prediction of total nitrogen in flue-cured tobacco with UV spectrometry].

Ultraviolet (UV) spectrum method was used to measure the spectra of flue-cured tobacco, and the spectra of different grades of flue-cured tobacco were compared. The samples were scanned in 210-360 nm with UV spectrometer. Further, the UV predicting models of total nitrogen of tobacco leaves were established by stepwise multiple regression method, principal components analytic method and partial least squares method. The results show that: (1) Predicting models of total nitrogen were established to adopt stepwise multiple regression method and principal components analytic method. (2) The models of total nitrogen of the different grade flue-cured tobacco established through scanning within the wavelength range of 230-290 nm were better for total nitrogen prediction. (3) The accuracy of total nitrogen prediction for flue-cured tobacco leaf with principal components analytic method was better than that of stepwise multiple regression method, and that of principal components analytic method is 78%. (4) The prediction model is different with different data treatment method. (5) The accuracy of prediction model could be improved by adopting fitting characteristic spectrum curve of total nitrogen. It is shown that the model of total nitrogen content prediction for flue-cured tobacco can be established by using UV spectrum. The model features good stability and can be used to determine accurately and speedily the total nitrogen content of flue-cured tobacco leaves without pollution.

Nitrogen contents of rice panicle and paddy by hyperspectral remote sensing.

The nitrogen content or crude protein content in rice grains is one of the important indices to evaluate the nutrition and taste quality of rice. Normal determination of their contents by chemical methods is highly expensive and time consuming. The hyperspectral reflectances of the canopy, flag leaf and panicle of 5 rice varieties are measured by a ASD FieldSpec Pro FR in field under 3 nitrogen support levels in maturing process. The nitrogen contents of stems, leaves, flag leaves, panicles and rice paddy and their crude protein contents are determined. The correlation among them is analyzed. The panicles nitrogen contents (%) are very significantly correlate not only to that of stems, leaves and flag leaves and chlorophyll contents (mg g(-1)) of flag leaves at milking and maturing stages, but also to the spectral reflectance rho(lambda), the first derivative spectra D(lambda) and RVI of canopy, flag leaf and panicle itself. The nitrogen contents (%) of rice paddy are very significantly correlative to that of stems and leaves and the spectral reflectance rho(lambda), the first derivative spectra D(lambda) and RVI of canopy at some wave bands at booting, milking and maturing stages. For the squared multiple correlation coefficients (R2) of estimating the nitrogen contents of panicle and paddy by canopies spectra, we find R2 > 0.80 at milking stage, R2 > 0.75 at maturing stage, but for the estimation of panicle by the spectra of flag leaf and panicle itself, we have R2 > 0.65. It indicates that it can be feasible for estimating the contents of nitrogen and crude protein in rice grains by hyperspectral remote sensing. It provide basis for monitoring rice quality by remote sensing.

[Estimation of rice LAI by using NDVI at different spectral bandwidths].

The canopy hyperspectral reflectance data of rice at its different development stages were collected from field measurement, and the corresponding NDVIs as well as the correlation coefficients of NDVIs and LAI were computed at extending bandwidth of TM red and near-infrared (NIR) spectra. According to the variation characteristics of best fitted R2 with spectral bandwidth, the optimal bandwidth was determined. The results showed that the correlation coefficients of LAI and ND-VI and the maximum R2 of the best fitted functions at different spectral bandwidths had the same variation trend, i.e., decreased with increasing bandwidth when the bandwidth was less than 60 nm. However, when the bandwidth was beyond 60 nm, the maximum R2 somewhat fluctuated due to the effect of NIR. The analysis of R2 variation with bandwidth indicated that 15 nm was the optimal bandwidth for the estimation of rice LAI by using NDVI.