确定性单光子源光子时域分布的高精度表征 (特邀)

As a core component of quantum information science and technology, single-photon sources exhibit unparalleled advantages in quantum communication, optical imaging, quantum sensing, and related fields. In particular, the photon temporal distribution, which characterizes the temporal coherence of single­photon sources, serves as a key parameter for evaluating their quantum performance. Consequently, precise measurement of photon temporal distributions in single-photon sources holds significant importance for both fundamental research and practical applications in quantum systems. Time-correlated Single­photon Counting (TCSPC) technology, as the standard technique for measuring photon temporal distribution, achieves single-photon-level detection sensitivity. However, the precision of TCSPC is fundamentally limited by the system’s Instrument Response Function (IRF), whose broadening effect directly compromises the accuracy of photon temporal distribution characterization. Through a systematic analysis of the TCSPC principle and the IRF impact on the temporal distribution measurements, three primary parameters deciding the ultimate precision were identified, including the pulse properties of excitation laser source, the performance of single-photon detector, and the measurement time-bin of TCSPC module. For the excitation laser source, when its pulse width is on the same timescale as fluorescence decay process of the investigated single-photon source, or when the repetition cycle is shorter than this decay process, the measured photon temporal distribution exhibits significant distortion, leading to a systematic overestimation of the resultant value. For the single-photon detector, its performance involves more complex factors, including timing jitter during photoelectric conversion, detection dead time effects, and electronic system response speed. Among these, timing jitter represents the primary factor limiting temporal resolution, preventing observation of fast decay components in single-photon source fluorescence dynamics. Substantial timing jitter thus impedes accurate measurement of short-lifetime components, introducing systematic deviations in the measured photon temporal distribution. Theoretically, the impact of IRF broadening on measurement results could be corrected through convolution algorithms. However, the effectiveness of such approach crucially depends on both the accurate characterization of the IRF and the signal-to-noise ratio during the measurements. Therefore, systematic investigation of IRF reduction and correction methods is essential for achieving precise photon temporal distribution measurements in single-photon sources. This study demonstrates high-precision characterization of photon temporal distributions in deterministic single-photon sources by systematically investigating the impact of the IRF on TCSPC measurements. Through analysis of the TCSPC technical principles, the theoretical foundation for precise measurement of photon temporal distribution is established. By employing the Levenberg-Marquardt algorithm based on nonlinear least squares, a fitting correcting the IRF effects for the photon temporal distribution analysis was established. This model incorporates IRF convolution while iteratively optimizing the model parameters to minimize the residual between the fitting result and experimental data. The implemented convolution algorithm was demonstrated to effectively correct the errors introduced by the IRF in the experimental measurements of photon temporal distribution in single-photon sources. Building upon the above analysis, the experimental measurements of IRF temporal distribution utilized a pulsed laser source with 532 nm wavelength, 12.5 ps pulse width, and 50 ns interval time between adjacent pulses. The output of excitation laser pulse was synchronized to an electrical signal, which serves as the trigger signal for the TCSPC module. The excitation laser photos reflected from the sample surface was detected by an avalanche photodiode(APD) single-photon detector. The detected photons were converted into stop signals by APD, whose output was connected to the TCSPC module. The TCSPC module recorded the time interval between the trigger and stop signals, then accumulated the counts into the corresponding time-bin during the measurement time. As a result, the temporal distribution of photons corresponding to the IRF was statistically obtained. To determine the Full Width at Half Maximum (FWHM) of the IRF dependent on the TCSPC time-bin, the experimental curves were normalized and fitted with Gaussian functions. The measurements of IRF with TCSPC time­bin of 16 ps, 32 ps, 64 ps, 128 ps, 256 ps and 512 ps yielded FWHM values of 0.410 ns±0.010 ns, 0.419 ns±0.013 ns, 0.433 ns±0.017 ns, 0.448 ns±0.026 ns, 0.545 ns±0.031 ns, and 0.791 ns± 0.014 ns, respectively. According to the IRF contribution formula, the contribution combining the single­photon detector’s timing jitter and the laser pulse width was calculated as 0.410 ns, 0.418 ns, 0.428 ns, 0.429 ns, 0.481 ns, and 0.603 ns for respective time-bins. Based on this IRF determination, two types of single-photon sources with distinct photon temporal distributions were characterized. One is a single Nitrogen-vacancy (NV) center in bulk diamond with well-known long coherent lifetime and another is a single-photon emitter in cubic silicon carbide(3C-SiC) crystal with multiple fluorescence decay channels. The single-photon property was determined by Hanbury Brown-Twiss (HBT) measurements, which utilizes the second-order intensity correlation function to evaluate the single-photon purity of the investigated emitters. Using the fitting model mentioned above, the measured effective photon temporal distribution of a single NV center was 16.70 ns±0.04 ns with 16 ps TCSPC time-bin, and 16.69 ns±0.04 ns with 32 ps TCSPC time-bin. For the 3C-SiC single-photon emitter, the measured effective photon temporal distribution was 1.67 ns±0.01 ns with 16 ps TCSPC time-bin. These results show excellent agreement with prior literature values. Moreover, the relative standard errors of all measurements are below 0.6%, demonstrating high-precision characterization capability of photon temporal distributions in deterministic single-photon sources. In summary, this study systematically investigated the impact of the IRF on TCSPC measurements and experimentally demonstrated high-precision measurement of photon temporal distributions in two types of deterministic single-photon sources. The relative standard errors of all measured photon temporal distributions are below 0.6%, validating the effectiveness of the developed fitted model in correcting IRF-induced errors. This work establishes a foundation for the application of photon temporal distribution measurement technology based on deterministic single-photon sources, such as quantum information processing, sensor development, biomedical imaging, and nanomaterial characterization.