Qiurong Yan

High-speed quantum-random number generation by continuous measurement of arrival time of photons

We demonstrate a novel high speed and multi-bit optical quantum random number generator by continuously measuring arrival time of photons with a common starting point. To obtain the unbiased and post-processing free random bits, the measured photon arrival time is converted into the sum of integral multiple of a fixed period and a phase time. Theoretical and experimental results show that the phase time is an independent and uniform random variable. A random bit extraction method by encoding the phase time is proposed. An experimental setup has been built and the unbiased random bit generation rate could reach 128 Mb/s, with random bit generation efficiency of 8 bits per detected photon. The random numbers passed all tests in the statistical test suite.

Multi-bit quantum random number generation by measuring positions of arrival photons

We report upon the realization of a novel multi-bit optical quantum random number generator by continuously measuring the arrival positions of photon emitted from a LED using MCP-based WSA photon counting imaging detector. A spatial encoding method is proposed to extract multi-bits random number from the position coordinates of each detected photon. The randomness of bits sequence relies on the intrinsic randomness of the quantum physical processes of photonic emission and subsequent photoelectric conversion. A prototype has been built and the random bit generation rate could reach 8 Mbit/s, with random bit generation efficiency of 16 bits per detected photon. FPGA implementation of Huffman coding is proposed to reduce the bias of raw extracted random bits. The random numbers passed all tests for physical random number generator.

The estimation of charge footprint size of ultraviolet photon counting imaging detector with induction readout.

The structure and work principle of an ultraviolet photon counting imaging detector based on wedge and strip anode with induction readout mode are introduced. Two methods of estimating the charge footprint size are presented. One way is theoretical calculation and simulation. The physical course of electrons is simulated from the microchannel plate output side to the readout anode. The calculated results show that the final charge footprint size is sensitive to the thickness of ceramic and not sensitive to the charge footprint size on the Ge layer. The other way is experimental image estimation. The final charge footprint size can be estimated according to the position where the light line of resolution board image begins to bend. Both methods show that the charge footprint size is sensitive to the ceramic substrate. The two methods are simple and effective for estimation of charge footprint size of photon counting imaging detector with induction readout.

X-ray photon-counting detector based on a micro-channel plate for pulsar navigation

The pulse time of arrival (TOA) is a determining parameter for accurate timing and positioning in X-ray pulsar navigation. The pulse TOA can be calculated by comparing the measured arrival time with the predicted arrival time of the X-ray pulse for pulsar. In this study, in order to research the measurement of pulse arrival time, an experimental system is set up. The experimental system comprises a simulator of the X-ray pulsar, an X-ray detector, a time-measurement system, and a data-processing system. An X-ray detector base is proposed on the basis of the micro-channel plate (MCP), which is sensitive to soft X-ray in the 1–10 keV band. The MCP-based detector, the structure and principle of the experimental system, and results of the pulse profile are described in detail. In addition, a discussion of the effects of different X-ray pulse periods and the quantum efficiency of the detector on pulse-profile signal-to-noise ratio (SNR) is presented. Experimental results reveal that the SNR of the measured pulse profile becomes enhanced as the quantum efficiency of the detector increases. The SNR of the pulse profile is higher when the period of the pulse is smaller at the same integral.

The resolution estimation of wedge and strip anodes

A new resolution estimation method for wedge and strip anode based on the single photon imaging configuration is provided. The limiting resolution estimation equation is deduced theoretically according to the threshold principle. The relation between the charge cloud and the covered electrodes is discussed, and the equivalent diameter number is calculated. The resolution equation for the position deviation amplitude or FWHM is provided if noise exists. The relation between the position deviation amplitude and the total charge deviation amplitudes is discussed. The constancy of the position deviation amplitudes versus positions is provided. The results calculated from these equations are discussed. According to the equations, it is indicated that the spatial resolution is affected by the detection system configuration and noise. These conclusions may be useful for the designing and performance improvement of future photon imagers.

Continuous measurement of the arrival times of x-ray photon sequence

In order to record x-ray pulse profile for x-ray pulsar-based navigation and timing, this paper presents a continuous, high-precision method for measuring arrival times of photon sequence with a common starting point. In this method, a high stability atomic clock is counted to measure the coarse time of arrival photon. A high resolution time-to-digital converter is used to measure the fine time of arrival photon. The coarse times and the fine times are recorded continuously and then transferred to computer memory by way of memory switch. The pulse profile is obtained by a special data processing method. A special circuit was developed and a low-level x-ray pulse profile measurement experiment system was setup. The arrival times of x-ray photon sequence can be consecutively recorded with a time resolution of 500 ps and the profile of x-ray pulse was constructed. The data also can be used for analysis by many other methods, such as statistical distribution of photon events per time interval, statistical distribution of time interval between two photon events, photon counting histogram, autocorrelation and higher order autocorrelation.

Decoding algorithms for improving the imaging performance of Vernier anode readout

The Long Slit Spectrograph is one of instruments onboard The World Space Observatory-Ultraviolet. Both the FUV (102-1700nm) and NUV (160-320nm) channels of LSS choose micro-channel plates (MCP) detector with anode readout in the focal plane. The MCP detectors with anode readout are typically used to provide photon counting imaging. According to the desired performance of LSS, the Vernier anode may be the optimum readout scheme. The Vernier anode is famous for its high spatial resolution, however, the original decode algorithms of the Vernier anode is susceptible to wrongly decode, when the charge acquisition is not precise enough and the footprint size of charge cloud collected by Vernier anode is not small enough and eventually results in the deterioration of photon counting image. In this paper, the causes leading to image deterioration is analyzed. The least-squares method was used to calculate the phase value to correct imaging distortions caused by charge measurement accuracy. The area ratio of each electrode covered by charge cloud is accurately calculated to improving the imaging results. The corrected algorithms are verified by experimental results and the results show that the correction methods can obviously improve the quality of the original photon counting image.

Temporal resolution of x-ray detector for pulsar navigation

Pulsar navigation is a promising new technique for space exploration because of its autonomous and deep space capability. Since the baseline of pulsar navigation approach is to observe the X rays (0.2~20keV) emitted from pulsars, a compact high temporal resolution X-ray detector is needed. In this paper an micro-channel plate(MCP) photon counting detector sensitive to X-rays is proposed. The detection system consists of a CsI photocathode, a 50mm diameter micro-channel plate (MCP) stack, a collection anode, a preamplifier, a constant fraction discriminator(CFD) and data acquisition(DAQ). The incident X-rays photons are absorbed by CsI and converted to photoelectrons, the electrons are multiplied by MCP and collected by the anode. Anode output signal is a fast pulse which need to be amplified by preamplifier and then fed to CFD circuit and DAQ for a precise timing. The total temporal resolution (ΔT) of the entire detection system could be determined by ▵tD, the intrinsic temporal resolution of cathode-MCP-anode, and ▵E the resolution of electronic system including preamplifier and CFD. The resolution of the detection system is tested to be 18.4ns in experiment.

Progress of NUV and FUV MCP-based photon-counting imaging detectors

In the World Space Observatory-Ultraviolet (WSO-UV) mission, the Long Slit Spectrograph (LSS) instrument will provide low resolution spectra in the range 102-320nm. Both the NUV (160-320nm) and the FUV (102-170nm) channels of LSS use microchannel plates (MCP) working in photon-counting modes as detectors. In this paper, the progress and parameters of NUV and FUV photon-counting imaging detectors were described. For the NUV detector, we developed the detector based on a sealed MCP-image intensifier which comprises input window, photocathode, MCP stack, Ge-layer and its ceramic substrate. To maximize the quantum efficiency, we adopted a Caesium Telluride (Cs2Te) photocathode, which was deposited on input window and mounted close to the MCP. For the FUV detector, because of the lower cut-off wavelength, there are no suitable window materials in this band and the open-faced design should be used to meet the requirements of the detection. Therefore, a Caesium Iodide (CsI) photocathode deposited on the input surface of the MCP was used to optimize detector efficiency. By using an existing wedge and strip anode (WSA), the imaging performance of the NUV and FUV detectors was tested respectively. Experimental results show that the quantum efficiency of Cs2Te is 12.1% (at 230nm), the spatial resolution of NUV and FUV detectors is better than 110μm, the dark count rate of NUV and FUV detectors is about 10.5- and 2.3-counts/s*cm2 respectively.