To characterize the accuracy of quantum state and quantum process,quantum state tomography and quantum process tomography as the basic tools,are developed.In our experiment,a single qubit is encoded in the cesium “clock states”.The fidelity of the prepared quantum state (-i|0〉+|1〉)2 is 097±002,which is characterized by the quantum state tomography.And we achieve an average fidelity of 096±003 of the quantum rotation gates Rx(π)、Rxπ2、Ry(π)、Ryπ2、Rzπ2 with the technique of quantum process tomography.The measures to further improve the fidelity is discussed.

Master equation of density operators in laser process can be concisely solved by virtue of thermo-entangled state representation.We consider the case in which one model light field in the two-mode squeezed vacuum state evolves in a laser channel.The evolution formula of the field density operator is given in the two-mode squeezed vacuum state initially.Its nonclassical properties,such as squeezing effect,anti-bunching effect,the violation of Cauchy-Schwartze inequality and the entanglement property between two modes,are investigated.Numerical results show that its nonclassical properties are weakened with the increase of dissipation time,until it disappears.On the other hand,its nonclassical properties are strengthened with the increase of squeezing parameter.

The effects of the second-layer environments’ cavity number N and the coupling strength κ between two-layer environments on the dynamics of quantum steering have been explored in detail for the weak and strong coupling regimes in this paper based on a quantum system consisting of two qubits, each interacting independently with its own two-layer environments.It has been shown that,with the increase in N and κ, quantum steering presents the oscillation phenomenon, and the survival time and values of which can be improved to some extent.In order to suppress the environmental decoherence, we discuss further the manipulation of quantum weak measurement and measurement reversal on quantum steering.The result shows that quantum steering can be protected effectively by the weak measurement method.

Single-photon detection laser ranging is an important method to achieve long distance and high precision ranging.The single-photon detector is easy to be saturated or even damaged in the daytime,and it is very difficult to identify the weak echo signal in the white light background,because the daytime background is about 1 million times of that at night.In this paper,a daytime single-photon detection laser rangefinder was developed.A two-stage filtering were used with a narrow-band interference filter and a FP etalon with a line width of 10 pm.The FP etalon was driven by a piezoelectric deflector to keep the center wavelength in line with the laser wavelength,so as to maintain the maximum transmission of the echo photons.The system could reduce the white light background noise effectively,and realized single-photon detection laser ranging with a PMT single photon detector at 532 nm in the daytime.In the experiment,the background noise was suppressed to 9×105 counts per second when the sunlight illuminance was 1.1×104 lx.The single-photon detection laser ranging was realized with a distance of 14 km and the signal-to-noise ratio was 16 dB.

Recognising that the key of the continuous-variable quantum key distribution system is difficult to extract,due to the low efficiency of its data reconciliation,we introduced the PEG (Progressive-edge-growth) algorithm to construct the check matrix of LDPC codes in a given distribution.The simulation results show that LLR-BP decoding on the check matrix constructed by the PEG can reach convergence faster than that on the check matrix constructed by the traditional Mackay method,under a distribution of the same degree.The reconciliation efficiency of the system reaches 934％.The extracted security key amount is 541 kb／s.The transmission distance can reach 445 km.

Multi-user quantum identify authentication scheme, based on the photon orbital angular momentum,is proposed.Authenticated users of the distributed network are encoded with quantum orbital angular momentum and then different nodes share two photon orbital angular momentum entanglement states with sub-servers.Firstly the trusted center of the network groups the quantum users with the phase factor of orbital angular momentum.Secondly authentication parties realize quantum teleportation of the orbital angular momentum by the entanglement of quantum orbital angular momentum.The protocol makes use of quantum information to guarantee the security of authentication system,and realizes multi-user authentication of network system by photon OAM.When the OAM state has two orthogonal polarization directions and the topological charge is equal to li(i=1,2,…,4),the quantum authentication efficiency can be improved 2×li by many times.

In a closed four-level coherent atomic system,we theoretically studied the effect of pump field and regulated field intensity on signal gain.Studies have shown that in a circulating four-level coherent atomic medium,the regulated field changes the distribution of population among the four energy levels,causing the signal field gain to be amplified.When added the regulated field (the intensity of regulated field is equal to that of the signal field),the signal gain is improved 12 times in contrast with N-type four-level system.Coherent pump field induces signal field amplification,and changing the pump field intensity can achieve signal field from the corresponding population number inversion gain to no population inversion gain.As the intensity of the pump field increases,the value of signal gain grows and then reduces.The closed-loop system may have important applications in optical amplification and gain effect.

The C6F12O molecule was optimized at different external electric field intensities (0000a.u.～0040a.u.) on the 6-31G(d) using the Minnesota density functional (M06-2X).The molecular structure,dipole moment and total energy of the ground state under different external electric fields were analyzed.Then,the excited state energy,wavelength,vibrator intensity and UV-vis spectrum of C6F12O molecules under various electric fields were studied by TD-DFT method.The results showed that the ground state and excited state properties of the molecule are dependent on the external electric field.As the external electric field increases,the total energy of the molecule gradually decreases and the dipole moment increases.The excited state energy of the molecule is generally reduced,and the C6F12O molecule becomes easy to excite.The absorption wavelength of C6F12O molecule increases from the ground state to the excited state and are mainly concentrated in the ultraviolet region.The vibrator intensity of excited state increases partly and the others decreases,and the variation is complex.With the increase of the external electric field,the absorption peaks at 132 nm and 162 nm in the UV-vis spectra are redshifted in the absence of external electric field.

CN radical plays an important role in the combustion of carbides.The low-excited state of CN was investigated by the ab initio calculation.Firstly,the molecular orbitals were determined by the Hartree-Fock self-consistent field approximation and optimized to use the complete active space self-consistent field theory.Then,the potential energy curves of three low excited states (X2Σ+,A2Π,and B2Σ+) for CN in the range of nuclear distance from 006 to 07 nm were obtained through multi-reference configuration interaction method.Considering the relativistic effects,the aug-cc-pV5Z-dk correlation-consistent basis set was selected in order to further improve the accuracy of the calculation.The vibration-rotation energy and constants of these electronic states were derived via solving the Schrodinger equation.Through fitting date listed above,the spectral constants(Te,Re,ωe,ωeχe,Be,αe),which are basically consistent with the experimental results,and Franck-Condon factors of three low excited states were acquired.Simultaneously,the transition dipole moments of the A2Π-X2Σ+ electric transition of CN have been computed,deducing the radiation lifetime τ and the oscillator strength f00 of the five low vibration levels.The calculated radiation lifetime is approximately 4 μs in accordance with the experimental measurements,which helps the study of the combustion dynamic.

Using a single highly focused fundamental-mode Gaussian beam could form an optical tweezer and load atoms,although optical tweezers generally choose to far away from the atom resonance transition line of the laser, optical tweezers intensity fluctuations will also lend to the atoms’ escape,so the lifetime of the atom in optical tweezers becomes crucial.In this experiment, acoustic optical modulator was used as the main component, and a set of external feedback control circuit was added to suppress the intensity noise in frequency domain and power fluctuation in time domain of 937.7 nm optical tweezers,reducing the heating parameters of atoms in optical tweezers, so as to effectively extend the trapping life of atoms in optical tweezers.The typical bandwidth is 17 kHz,noise suppression is 10 dB, and the time-domain laser intensity fluctuation could be reduced from a peak-to-peak fluctuation of ±1350％ to ±0036％, effectively reducing the intensity fluctuation of optical tweezers. The experimental results showed that the trapping lifetime of single cesium atom in 937.7 nm optical tweezers could be extended from 200 ms to 1 180 ms.It provides sufficient time for the subsequent preparation and excitation of atomic states, ensures the capture of atoms, improves the success rate of experiments, and saves the time of experiments.

Based on the four-component coupled nonlinear Schrdinger equation with variable gain coefficient,the two-soliton solutions with three bright soliton components and one dark soliton component are obtained via the Hirota bilinear method.Simultaneously,the asymptotic limit and transmitting characteristics of the two-soliton solutions are discussed in detail.The results show that the elastic collision,inelastic collision and bound state transmission of the two-soliton solutions can be obtained by selecting the parameters reasonably.

On the NV-based quantum information lab bench,we need to apply a specific sequence of microwave RF pulse signals to the diamond NV center.In order to apply a specific sequence of microwave RF pulse signals to the sample,we use a slotline with the characteristics of low loss and no cutoff-frequency to design and implement a planar circuit radiation structure,which can efficiently modulate the microwave RF pulse signal into a microwave field and act on the diamond NV center to realize quantum state regulation.The design is based on the principle that the traditional slotline is used as the main transmission line and the T-shaped slotline is used as the power division structure,and the Ω-type ring is used as the radiation structure.A part of the power flow in the main transmission line is fed into the Ω-type ring to obtain a strong microwave field. Compared with the traditional lithography micro-nano process,this design uses the laser etching and electrochemical copper plating processes to achieve low-cost fabrication of the radiation structure.After testing by instruments such as network analyzer, the radiation structure has been applied to the NV quantum information test bench, and the alternating magnetic fields of about 4.48 Gauss and 48.49 Gauss are respectively obtained near the high frequency 2．8 GHz and low frequency 7.1 MHz operating frequencies.

For analyzing the situation that electron oblique incidence through graphene, it is assumed that graphene layer is as a barrier.The width of the barrier is D and the height is V0.The energies of the electrons that pass through from the incidence layer, the graphene layer, and the transmissive layer are set to E1,E2 and E3 (E1>E2>E3).The transmittance of the electrons is obtained by Schrdinger equation and the continuities of the wave function and its derivative at x=0 and x=D.The figures of the transmissive are drawn using Matlab.The results show us three aspects.The first one is that the transmittance is independent of the incident angle but related to energy.The second one is that the higher the incident energy is, the greater the energy is after passing through the barrier, that is, the better the transmittance.The narrower the barrier width is, the higher the transmission energy is.The third one is that the transmitted energies are 555％, 320％, 152％ of the height of the barrier at the widths of the barrier are 1, 2, 3 times of the length of the tunneling effect when the incidence energy is the 07 times of the height of the barrier.

The spin coherence time of NV-with high concentration at room temperature is limited by the paramagnetic impurity and its spin, which is not conducive to the magnetic sensing with high sensitivity. To increase the coherence time, the dynamic decoupling (DD) process for NV- color center ensemble is studied in this paper. When the external magnetic field is fixed at 40 G,the resonant microwave frequency of |ms=0>→|ms=±1> is determined via continuous-wave optical magnetic resonance (CW-ODMR) spectroscopy. The Rabi oscillations between the |ms=0>→|ms=+1> with different microwave power have been observed and the optimal π-pulse length can be determined. Based on the typical CPMG-n sequence, the DD process with different number of optimal π-pulse is also studied. At a maximum input power of 130 mW, the optimal π-pulse length is 288 ns. Combined with CPMG-32 sequence, the coherence time is increased from 372(3) ns to 87(1) μs. These results show that we already have the basic technology of improving the coherence time with manipulation of quantum state, which is the foundation for the quantum magnetic detection with high sensitivity.

In this paper,a spatial temperature distribution model of laser crystal was established by means of heat conduction equation in case of the master-oscillator power amplifier (MOPA) configuration.On this basis,the thermal distribution of laser crystals in single-end-pumped and double-end-pumped amplifiers were numerically compared,concluding that the spatial temperature distribution at the laser crystal of double-end-pumped MOPA configuration was superior as compared to that of the single-end-pumped MOPA configuration.Furthermore,based on analyzing the influence of the parameters of the laser crystal and the beam waist radius of the pump source on the thermal distribution of the laser crystal,we employed a laser crystal with doped concentration of 02％ and length of 19 mm as well as a pump source with waist radius of 650 μm,constructed the double-end-pumped MOPA with uniform thermal distribution.

Based on spatial mode interference,tilt-locking technique is a flexible and convenient way to stabilize laser frequency or to lock optical cavity.In this paper a modification of tilt-locking is described and experimentally demonstrated.The method uses a non-resonant first-order spatial mode TEM01 as phase reference,and utilizes the interference of the TEM01 mode and the TEM00 mode for locking.An obstacle is added in the reflected light path of the optical cavity to block half of the reflected light beam.The passing half of reflected beam is detected by a single-pixel detector,instead of a split detector,to derive the error signal for locking TEM00mode resonant frequency of optical cavity to laser frequency.An optical cavity can be stably locked over four hours with this method.This modification makes tilt-locking technique become more convenient and flexible.

The output characteristics of LD end-pumped single-longitudinal-mode (SLM) 3 μm lasers are studied theoretically.Based on the analysis of energy processes of the Er:YAG laser system,a rate equation model with the influences of thermal effect taken into account is established,and the effects of the temperature and doping concentration and length of the laser crystal,the pump waist to laser waist ratio,the transmission of output coupler,the insertion loss of the optical diode on the output behaviors of the continuous wave (CW) SLM 3 μm laser are researched.The model can be used to guide the design and optimization of a high power CW SLM Er:YAG laser operating at 3 μm.

In order to facilitate the operability of continuous variable quantum optical experiment, an automatic locking system with microcontroller (MCU) is designed and is used in the cavity length locking of the optical mode cleaner. We use analog to digital conversion to identify the signal, the MCU to complete the relevant data analysis and calculation, and then digital to analog conversion to complete the signal output. Finally, the automatic locking of cavity length is realized. When the cavity is unlocked, the system can automatically switch working mode to achieve re-locking. The re-locking time is less than 01 s, and the fluctuation of intensity is less than 1％.