Study On Control And Detection Systems For Squeezed State Of Light With Continuous Variable

With the development of quantum optics and quantum information science, we astonished find that quantum noise suppression and quantum entanglement are very information resources, which can accomplish the impossible tasks in the frame of classical information and computation, such as utilizing the entangled state of light to realized the quantum teleportation, quantum dense coding, quantum entanglement swapping and quantum computing etc. In the recent years, quantum information science is developing toward the practical application direction. However, the squeezed state of light as the fundamental light-source quantum information processing for continuous variables should posses the characteristics of miniaturization, integration, digitization and stable running for a long time.All solid state dual wavelength single frequency laser is the most important part of the squeezed state of light-source for continuous variable. Firstly, in the process of generating the squeezed state of light for continuous variable, the two beams of coherent light field generated by the all solid state dual wavelength single frequency laser as pump source is used as the pump light and signal light, respectively. Secondly, in the system of the balanced homodyne detection for the squeezed state of light, the coherent state as bright local oscillator which is used to amplify and probe the signal field (squeezed state) is the fundamental frequency of laser output, and generate the corresponding shot noise limitation (SNL). Therefore, the performance of all solid state single frequency lasers will directly affect the generation and measurement of the squeezed state of light field.In order to obtain the laser output with these characteristics of stable higher power, single frequency and ideal beam quality, Yaohui Zheng experimental group put forward some experimental solutions for laser cavity design. But we focus our concentration on how to design and optimize the high precision temperature control system. In view of the shortcomings of large volume, high noise and the poor accuracy of temperature-control for traditional analog temperature control system. We design and build a high-precision digital temperature-control system with these characteristics including miniaturization, intelligentize, low power consumes and excellent stability. Meanwhile, it is very important not only to generate highly squeezed light but also to measure accurately the highly squeezed light, many dedicated researches have been developed in order to explore an effective detection method and a high-performance photodetector for measuring accurately quantum noise suppression. However, balanced homodyne detection (BHD) method can effectively cancel this classical noise, amplify the measured state, and characterize any general quadrature of the measured state, which represents a well-established technique for drawing upon the features of squeezed light.The main research contents of the thesis are as following:1、We design and build the control system for squeezed state of light with continous variable, and apply to 1064 nm squeezed state of light. The control system integrates a compact, intelligent laser control system, an integrated lock control system and a high-performance balanced homodyne detection system.2、We design and build a high-precision digital temperature-control system (HPDTCS) with these characteristics including miniaturization, intelligentize. Applying the HPDTCS to control an all-solid-state single-frequency green laser, we devise the software to realize automatic operation, mistake prevention, alarm and interlock protect functions. HPDTCS has been sold as a product. The speed-change integral PID control algorithm and the high-resolution pulse width modulation (HRPWM) technology are utilized in this system to control the drive current of the thermoelectric cooler (TEC). Depending on the difference of the temperature efficient of the thermistor under higher and lower temperature, the different temperature detection circuits of constant current source and constant voltage source are applied, respectively. The HPDTCS consists of three lower (10 to 40℃) and a higher (120 to 160℃) temperature-control modules with the precision of ±0.005℃. Ultimately, the problem of poor stability of squeezed state light caused by poor temperature control precision and poor power stability is solved, and the small volume, low noise and low power consumption are achieved.On the basis of the theoretical background of the balanced homodyne detection (BHD), we analyze quantitatively the influence of the non-ideal BHD including the reflectivity of 50/50 beamsplitter, the efficiency of interference and the common mode rejection ratio (CMRR) on the measured squeezing degree, and build the relation of the deviation value, the real squeezing degree, the reflectivity of 50/50 beamsplitter, the efficiency of interference and the CMRR, which is very important to infer the real squeezing degree from the measured squeezing degree, the ratio of 50/50 beamsplitter, the efficiency of interference and the CMRR.3、The design is based on the self-subtraction photodetector scheme of balanced homodyne detector (BHD) and the equivalent circuit of a photodiode. We divide the influence of photodiodes on the common mode rejection ratio (CMRR) into two parts, including magnitude and phase of output signal. The discrepancy of quantum efficiency and dark current affects magnitude of output signal of photodiodes, which is compensated by adjusting the splitter ratio. The difference of the equivalent capacitance and resistance affects the phase of output signal of photodiodes, which is compensated by the differential fine tuning circuit and adjustable bias voltage circuit. Combined with the former design work, a balanced homodyne detector, with the feature of low-noise, high-gain, and high CMRR, is experimentally obtained with two arbitrary photodiodes with the same model with a maximum CMRR and clearance of 75.2 dB and 37 dB, respectively. In addition, the photodetector can operate linearly in larger power range. With the local oscillator power increased, a clearance of 3 dB at 2 MHz could be obtained from the clearance of 20 dB for 1 mW to the clearance of 37 dB for a saturation power of up to 54 mW With these parameters, the developed homodyne detector can be used for measuring accurately the squeezed state.