Low-noise, transformer-coupled resonant photodetector for squeezed state generation

1.55 GHz balanced homodyne detector with high gain flatness based on low noise amplifier

In this paper, a model for simulating the shot noise power and the electronic noise power of a balanced homodyne detector (BHD) using cascaded low noise amplifiers (LNAs) is presented. Moreover, the factors influencing the enhancement of BHD gain flatness are analyzed. Based on these theories, a BHD with a large clearance between shot noise and electronic noise, along with a flat broadband frequency response, is designed using LNAs and an optimized printed circuit board design. According to the experimental measurements, the bandwidth for 1 dB flatness reaches 1.4 GHz with the -3 dB bandwidth extending up to 1.55 GHz. With a 4 mW optical signal input, a signal-to-noise ratio of 12 dB is obtained at 1 GHz. The BHD exhibits excellent linearity for shot noise output up to an 8 mW optical signal input and a tested common mode rejection ratio of 63 dB. This developed BHD is well-suited for applications in high-speed continuous variable quantum key distribution and quantum random number generation.

Simulation of high signal-to-noise ratio resonant photodetector for homodyne measurement and its verification

In this paper, two models for simulating the shot noise and electronic noise performances of resonant photodetectors designed for homodyne measurements are presented. One is based on a combination of a buffer and a low-noise amplifier, and the other is based on an operational amplifier. Through the comparisons between the numerical simulation results and the experimentally obtained data, excellent agreements are achieved, which show that the models provide a highly efficient guide for the development of a high signal-to-noise ratio (SNR) resonant photodetector. Furthermore, we demonstrate a high SNR resonant photodetector for homodyne measurements at the 147 MHz optical sideband, achieving a 20.8 dB SNR of the shot noise to the electronic noise with a 2 mW optical signal input, utilizing a combination of a buffer and a low-noise amplifier. Concurrently, we have obtained another resonant photodetector at the 1.14 GHz optical sideband, which exhibits a 13 dB SNR based on an operational amplifier.

Broadband and robust Mach-Zehnder interferometer for Rydberg atomic system

We present a broadband and robust Mach-Zehnder interferometer (MZI) with meter-scale arm length, aiming to acquire the full information of an atomic system. We utilize a pre-loading phase shifter as servo actuator, broadening the servo bandwidth to 108 kHz without sacrificing the size of the piezoelectric transducer (PZT) and mirror. An auxiliary laser at 780 nm, counter-propagating with the probe laser, is employed to achieve arbitrary phase locking of the MZI, boosting a phase accuracy of 0.45 degrees and an Allan deviation of 0.015 degrees, which breaks the current record. By utilizing our robust MZI, the measurement accuracy of atomic system can be theoretically predicted to improve by 2.3 times compared to the most stable MZI in other literatures. In addition, we also demonstrate the sensitivity improvement in imaginary part and real part of the susceptibility in virtue of the completed interferometer, which exhibits tremendous potential in atom-based measurement system.

Stabilization improvement of the squeezed optical fields using a high signal-to-noise ratio bootstrap photodetector

High-precision cavity locking is crucial for squeezing optical fields. Here, a bootstrapped low-noise photodetector is utilized in the generation process of the squeezed state of light. This process is based on a combination of a modified trans-impedance amplifier (TIA) circuit and a two-stage bootstrap amplifier circuit. This not only achieves high-precision and long-term stable locking of the optical cavity, but it also improves the degree to which the light field is squeezed. The experiment results show that the detector has a high signal-to-noise ratio (SNR) of 26.7 dB at the analysis frequency of 3 MHz when measuring the shot noise with an injection optical power of 800 µW, and the equivalent optical power noise level is lower than 2.4 pW/Hz in the frequency range of 1-30 MHz. Moreover, the squeezing degree of the quadrature amplitude squeezed state light field can be improved by more than 34.9% when the detector is used for optical cavity locking. The photodetector is useful in continuous variable (CV) quantum information research.

Realizing a high-efficiency 426nm laser with PPKTP by reducing mode-mismatch caused by the thermal effect

We report on a high conversion efficiency tunable laser at 426 nm by adopting an external frequency-doubling cavity pumped by a diode laser. For the frequency-doubling process at 426 nm, the major challenge of increasing the conversion efficiency is mode-match degradation originating from the severely thermal effect. Here, we find that the center of the equivalently thermal lens is not at the center of the nonlinear crystal. We minimize the variation of beam parameters of the Gaussian beam in the external cavity by optimizing the center of the thermal lens to beam waist. As a result, the mode-match degradation is reduced as the incident power is increased. Finally, a 405 mW blue light is obtained with the conversion efficiency of 81%.

500 MHz resonant photodetector for high-quantum-efficiency, low-noise homodyne measurement

We design and demonstrate a resonant-type differential photodetector for a low-noise quantum homodyne measurement at 500 MHz optical sideband with 17 MHz of bandwidth. By using a microwave monolithic amplifier and a discrete voltage buffer circuit, a low-noise voltage amplifier is realized and applied to our detector. 12 dB of signal-to-noise ratio of the shot noise to the electric noise is obtained with 5 mW of a continuous-wave local oscillator. We analyze the frequency response and the noise characteristics of a resonant photodetector, and the theoretical model agrees with the shot noise measurement.