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Quantum-inspired imaging techniques have been proven to be effective for LiDAR with the advances of single photon detectors and computational algorithms. However, the quantum-limited performance is still far from its ultimate limit set by the quantum fluctuations of signal and noise photons. In this work, we propose and demonstrate LiDAR from the detection perspective for approaching quantum-limited performance. A photon-number-resolving detector is introduced to accurately reconstruct the echo signals in a wide photon-flux range and an active photon number filter is further developed to overcome the heavy background noise. The Fisher information of this LiDAR based on a coherent source is only 0.04 dB below the quantum limit in intensity detection when mean signal photon number is 10. An improvement of 41.17 dB in the signal-to-background ratio is achieved with the proposed LiDAR in daytime, and the accuracy of intensity estimation is consistent with the theoretical prediction, which helps to improve the quality of reconstructed images. This work provides a fundamental strategy for constructing a noise tolerant LiDAR approaching quantum-limited precision.

A superconducting nanowire single-photon imager (SNSPI) uses a time-multiplexing method to reduce the readout complexity. However, due to the serial connection, the nanowire should be uniform so that a common bias can set all segments of the nanowire to their maximum detection efficiency, which becomes more challenging as the scalability (i.e., the length of the nanowire) increases. Here, we have developed a 64-pixel SNSPI based on amorphous Mo

A fan-out circuit is a basic block for scaling up digital circuits for overcoming the limited driving capability of a single logic gate. It is particularly important for superconducting digital circuits as the driving power is typically weak for having high energy efficiency. Here, we design and fabricate a fan-out circuit for a superconducting nanowire cryotron (nTron) digital circuit. A classic splitter tree architecture is adopted. To transmit switching signal and avoid crosstalk among nTrons, we introduced an “R–L–R” interface circuit. Experimentally, a two-stage splitter tree of a fan-out number of four was demonstrated. Correct operation was observed with a minimum bit error rate (BER) of 10−6. The bias margin was 10% at BER of 10−4. The average time jitter was 82 ps. Moreover, crosstalk was not observed. Based on these results, we envision that the fan-out circuit can be used in future development of superconducting-nanowire-based circuits.

Multilayer superconducting nanowire single-photon detectors (SNSPDs) have exhibited several advantages, such as increased detection efficiency, reduced polarization sensitivity, and scaling up to large arrays. However, monolithic fabrication of such multilayer devices is challenging. In this work, a hybrid integration method has been introduced by etching SNSPDs into the membrane microchips, followed by the pick and place transferring process. This method has been verified by stacking two SNSPDs orthogonally. Both detectors show near saturated detection efficiencies and low timing jitters. Furthermore, thermal coupling effects have been observed between the two SNSPDs. The photon detection pulses from either detector can trigger the other one almost deterministically with a latency of several nanoseconds. This method offers a flexible way to fabricate multilayer SNSPDs or integrate them with other heterogeneous devices.

A superconducting nanowire single-photon imager (SNSPI) uses a time-multiplexing method to reduce the readout complexity. However, due to the serial connection, the nanowire should be uniform so that a common bias can set all segments of the nanowire to their maximum detection efficiency, which becomes more challenging as the scalability (i.e., the length of the nanowire) increases. Here, we have developed a 64-pixel SNSPI based on amorphous Mo80Si20 film, which yielded a uniform nanowire and slow transmission line. Adjacent detectors were separated by delay lines, giving an imaging field of 270 µm × 240 µm. Benefiting from the high kinetic inductance of Mo80Si20 films, the delay line gave a phase velocity as low as 4.6 µm/ps. The positions of all pixels can be read out with a negligible electrical cross talk of 0.02% by using cryogenic amplifiers. The timing jitter was 100.8 ps. Saturated internal quantum efficiency was observed at a wavelength of 1550 nm. These results demonstrate that amorphous film is a promising material for achieving SNSPIs with large scalability and high efficiency.

Photon number resolving (PNR) is an important capacity for detectors working in quantum and classical applications. Although a conventional superconducting nanowire single-photon detector (SNSPD) is not a PNR detector, by arranging nanowires in a series array and multiplexing photons over space, such series PNR-SNSPD can gain quasi-PNR capacity. However, the accuracy and maximum resolved photon number are both limited by the signal-to-noise (SNR) ratio of the output pulses. Here, we introduce a matched filter, which is an optimal filter in terms of SNR for SNSPD pulses. Experimentally, compared to conventional readout using a room-temperature amplifier, the normalized spacing between pulse amplitudes from adjacent photon number detections increased by a maximum factor of 2.1 after the matched filter. Combining with a cryogenic amplifier to increase SNR further, such spacing increased by a maximum factor of 5.3. In contrast to a low pass filter, the matched filter gave better SNRs while maintaining good timing jitters. Minimum timing jitter of 55 ps was obtained experimentally. Our results suggest that the matched filter is a useful tool for improving the performance of the series PNR-SNSPD and the maximum resolved photon number can be expected to reach 65 or even large.

Superconducting niobium nitride (NbN) hot electron bolometers (HEBs) have been used widely in the astronomical observations with its low noise temperature [1] (a few times of the quantum noise limit) as heterodyne detectors. On the other hand, with high temperature coefficient of resistance (TCR) and low noise characteristics, NbN HEB can be considered as direct detectors. Combined with NbN material’s quick response property (response time:~ps), NbN HEB direct detector can be used in quick terahertz (THz) imaging and weak THz ultrashort pulse signal detection. A direct detector system similar to the microwave stability system[2] in our lab has been constructed. The injected microwave is used to suppress the superconducting current and bias the HEB to an optimum bias point combined with the constant DC voltage source. The bias current changes corresponding to the incident THz signal power is read out by the dynamic signal analyzer. Compared to the thermal bias method which used the heating methods to heat the HEB to its critical temperature, the proposed method can enhance the direct detector’s stability and decrease the consumption of the liquid helium, which is key for the long time observations in the astronomical field and so on. More importantly, we found that our method can enhance the TCR of the NbN HEB from 8.45/K with the thermal bias method to 961/K. We obtained the noise equivalent power (NEP) of 1.4×10-12 W/Hz1/2 at 4.2 K and 0.65 THz. This value is mainly limited by the read out circuit at this moment. The response time of 86 ps is obtained in the separate measurement. Further improvement of NEP can be realized with optimizing the read out circuit.

Mixed strains were used to increase the hydrolysis degree of materials during fermenting. Tilapia scraps and soybean meal were mixed by 1:1 and Bacillus subtilis, yeast and lactic acid bacteria were added. The optimal quantity of strains was determined by hydrolysis degree through single factor experiments and orthogonal experiments. After all, The molecular weight distribution of raw material and products was analyzed by high performance size exclusion chromatography (HPSEC). The results showed that the optimum conditions were as follows: the inoculation amount of Bacillus subtilis, the yeast and the lactic acid bacteria was 0.6‰, 0.06‰ and 0.0015‰, respectively. And the hydrolysis degree of materials increased from 10.3% to 27.3%. The hydrolysis degree of materials increased markedly by adding mixed strains.

Employing the flexible tetrapodal ligand 1,2,3,4-tetra-(4-pyridyl)-butane (TPB) along with fumaric acid (H2FMA) as the bridges, a metal-organic framework of [Zn(TPB)(FMA)·(2H2O)] (1) was obtained and characterized by elemental analysis, spectral method (IR), single crystal X-ray diffraction, thermal gravimetric analysis (TGA) and fluorescent property. This polymer exhibits a three dimensional (3D) dense network with an interesting (4,4)-connected PtS topology. It also displays good thermal stability and strong photoluminescence in the blue region band. Thus it may serve as a candidate of thermally stable blue-light-emitting photoluminescent material.

Employing the tetrapodal compound 1,2,3,4-tetra(4-pyridyl)thiophene (TPT) as a bridging ligand, a new metal–organic framework was obtained and characterized by single crystal X-ray diffraction, [Cd(TPT)(N3)2·(H2O)] (1). This polymer exhibits a 2D layer network and an unprecedented 3,4-connected topology, which is constructed from the three-connector TPT and EE azido bridges. It also displays good thermal stability and strong photoluminescence in the blue regionband thus may serve as a candidate of thermally stable blue-light-emitting electroluminescence material. The nature of electronic transitions in the photoluminescent process has also been investigated by means of time-dependent density functional theory (TDDFT) calculations and molecular orbital analyses, which shows that the luminescent property is ligand-based.

Employing the symmetrical ligand 1,2,3,4-tetra-(4-pyridyl)-butane (TPB) as bridges, two novel Zn(II) coordination polymers were obtained and characterized by single crystal X-ray diffraction: [Zn(TPB)0.5(NCS)2] (1) and [Zn(TPB)(N3)2] (2). Polymer 1 features a 2D network with herringbone structural motif constructed by TPB, while polymer 2 shows a dense 3D network connected by TPB and μ1,3-N3- bridges. In the former, the TPB ligand acts as a four-connector, while in the latter it acts as four-connector and linear bridge. Both 1 and 2 exhibit strong fluorescent emissions in the solid state, which may be of significance in the field of photoactive materials.

The microstructure and microwave dielectric properties of inhomogeneous SiC-AlN solid solutions, hot pressed under a pressure of 40 MPa, have been investigated. Microstructure analysis detected the existence of BN in the resulted samples, which may be a reason that homogeneous solid solution was not formed for the samples with AlN content higher than 20%. The dc resistivity of the solid solutions at room temperature varies from 8 × 103 Ω m to 1 × 109 Ω m. Ion jump and dipole relaxation losses are the main mechanism of dielectric losses.

The structures of two ion-pair complexes, which consist of 1-(4′-R-benzyl)pyridinium (R = NO2 (1), Br (2)) and bis(maleonitriledithiolato)cuprate(II), have been determined by X-ray single crystal analyses, and the results show the stacking patterns in 1 and 2 are different from each other although the difference between the molecular structures of these complexes is only the substituent of the benzene ring, which may arise from the difference of interactions between cations and anions in these two complexes. Complex 1 crystallizes in the non-centrosymmetric space group P1, and dielectric measurements shows ferroelectric behavior with a small hysteresis loop. Quantum chemistry calculation further indicate the electric dipole in a unit cell is 56.5509 Debye, and DSC analysis reveal a Tc of 377 K, from the paraelectric to the ferroelectric phase. The magnetic susceptibilities of these two complexes measured in the temperature range 1.8–260 K show an antiferromagnetic coupling feature between neighboring Cu(II) ions with θ = −0.580 K for 1 and −2.167 K for 2. The polycrystalline EPR spectra of the two complexes at room temperature are different from each other, characterized axial g tensors are g‖ of 2.09, g⊥ of 2.02 for 1, and g‖ = 2.05, g⊥ = 2.03, A‖ = 40.6 × 10−4 cm−1 for 2.

Ion-pair complexes consisting of the [Fe(mnt)2]− anion and [RBzPy]+ cations [R = NO2(1) or Cl (2)] have been prepared and characterized by elemental analysis and i.r. spectroscopy. The single crystal structure of (1) shows that the [Fe(mnt)2]− anions are dimeric, and that the coordination geometry of each Fe atom is square pyramidal. The most significant structural feature of (1) is that anions and cations form completely separate columns and π–π interactions occur within the cation columns. Thermal variations of χmT for the complexes indicated antiferromagnetic coupling within the dimer.

Aromatic polyamic acid alkyl ammonium salt exhibits very good transfer behavior under suitable deposition conditions. A superconducting thin film of YBa2Cu3Ox (YBCO) on Langmuir–Blodgett film (LB) has been obtained when the substrate temperature is higher than 500°C. Superconducting edge junctions of (Pb—In)/LB/(Pb—In) and YBCO/LB/YBCO incorporated with polyimide LB films were fabricated. Their current–voltage characteristics are discussed in terms of the temperature stability of polyimde LB films. © 1994 John Wiley & Sons, Inc.

Terahertz time-domain spectroscopy (THz-TDS), which directly measures the THz wave's temporal electric field, can give the amplitude and phase of the THz wave pulse simultaneously. THz-TDS is attracting more attention among scientists. InP with short carrier average collision time and low effective mass is growing up as one of the best photoconductive materials for emitting and detecting THz waves. An n-type InP of 0.35 omega x cm was characterized over the range from 0.2 to 4 THz at room temperature in the present paper with THz time-domain spectroscopy, which was placed in a closed box purged with dry nitrogen gas. Some THz optical properties, such as complex refractive index, dielectric constant, and conductivity, were extracted, based on more exact iterative method with new initial function. Drude model was also applied for simulation, which fitted well with the experimental results. Finally, the carrier average collision time, density and mobility of the InP were also characterized.

Lying between microwave and infrared, terahertz waveband provides us with many chances for scientific research and practical applications, while there are still many challenges. It has been demonstrated that imaging is one of the fields where terahertz technology can be of great value compared with other competing technologies. In this talk, Prof. Wu shall discuss some of our imaging results using either continuous-wave or pulsed terahertz sources. Strong absorption of terahertz signals in water can be a problem in imaging of biological objects. To overcome the difficulties caused by this problem, they have explored the possibility of using superconducting devices in this field which are believed to be the most sensitive detectors at terahertz waveband so far. Also addressed in the talk will be the results relevant to this issue.

Versatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses. Light: Science & Applications (2015) 4, e253; doi:10.1038/lsa.2015.26; published online 27 February 2015

Using a superconducting weak link (bridge) made of YBCO, we have successfully demonstrated the internal oscillation-mixing at either X or Ka band.

In the title complex, 2-methyl-1-(4-nitrobenzyl)pyridinium bis(1,2-dicyanoethene-1,2-dithiolato)nickelate(III), (C(13)H(13)N(2)O(2))[Ni(C(4)N(2)S(2))(2)], the most prominent general structural feature of the complex is the completely segregated columnar stacks of anions and cations. Within the cation column, there may be stacking interactions between adjacent nitro groups and benzene rings.