| 摘要: | 隨著量子科技的發展，其中量子通訊以及量子計算對具有光子數解析能力的單光子偵測器需求日益旺盛，並以此命名為光子數解析偵測器(photon number resolving detector, PNRD)。以線性光學量子計算(Linear Optical Quantum Computing, LOQC)中的CNOT閘(Controlled-NOT gate)為例，需要PNRD用來運行也可以對錯誤運算進行校正。在眾多光偵測器種類中，本文以III-V族單光子雪崩二極體(single-photon avalanche diode, SPAD)來做研究，不僅僅是因為SPAD比其他光偵測器製程更簡單且穩定，也剛好能運用在量子通訊1550 nm波段的量子密鑰分發(quantum key distribution, QKD)上當接收光子的偵測器。要在III-V SPAD上達成光子數解析其中之一是必須在崩潰電流飽和之前量測，這意味著要在低超額偏壓時就能觀察到崩潰訊號，但往往其都會被電容訊號給蓋住。另一個則是後脈衝效應(afterpulsing effect)，III-V族由於缺陷較多導致越高頻時其干擾的更為嚴重。
因此本研究用自製的InGaAs/InAlAs SPAD以頻率操作在300 MHz的正弦閘控模式其中的短閘控寬度能抑制暗計數和後脈衝效應，且用濾波技術消除電容訊號使崩潰訊號足以辨別，接著在不同溫度下量測尋找元件的最佳特性，最後在溫度200 K時在波長1550 nm雷射下成功解析出5顆光子，並與100 MHz的脈衝閘控相比有更好的PNR表現，最後以不同頻率以及不同累增層厚度探討其對PNR性能的影響。;With the advancement of quantum technology, the demand for single-photon detectors with photon-number resolving capability has been increasing, particularly in the fields of quantum communication and quantum computing. This has led to the development of detectors known as photon number resolving detectors (PNRD). Taking the example of the Controlled-NOT gate (CNOT gate) in linear optical quantum computing (LOQC), PNRD is essential for its operation and correction of error computations. Among various types of photodetectors, this study focuses on III-V single-photon avalanche diodes (SPADs) due to their simpler and more stable fabrication process compared to other detectors. Additionally, III-V SPADs are suitable for quantum key distribution (QKD) in the 1550 nm wavelength range for quantum communication. Achieving photon-number resolving on III-V SPADs requires measurements before reaching the breakdown current saturation, which means observing the breakdown signal at low excess bias. However, this signal is often overshadowed by capacitive signals. Another challenge is the afterpulsing effect, where the interference becomes more severe at higher frequencies due to the higher defect density in III-V materials.
Therefore, in this study, a self-made InGaAs/InAlAs Single-Photon Avalanche Diode (SPAD) was employed to operate in a sinusoidally gated mode at a frequency of 300 MHz. The use of a short gate width in this mode helped suppress dark counts and afterpulsing effects. Additionally, filtering techniques were applied to eliminate capacitance signals, ensuring that breakdown signals were discernible. Subsequent measurements were conducted at different temperatures to identify the optimal characteristics of the device. Finally, at a temperature of 200 K and under a wavelength of 1550 nm laser, the successful resolution of 5 photons was achieved. The performance in terms of Photon Number Resolving (PNR) showed superior results compared to a 100 MHz pulse-gated system. The study concluded by investigating the impact of varying frequencies and different multiplication layer thicknesses on the PNR performance. |
