We report an experiment that improves the signal-to-noise ratio of homodyne detection for ultrafast quantum light by exploiting temporal correlations in the detector response, resulting in an increase in measured squeezing.
Ultrafast continuous-variable quantum states offer new opportunities for advanced quantum technologies, but efficient homodyne detection of these states remains challenging. Here, we present a method for efficient ultrafast homodyne detection by exploiting temporal correlations in detector signals. By optimizing the temporal weight used to extract quadrature outcomes, we achieve a substantial increase in the signal-to-noise ratio of ultrafast homodyne detection, thereby improving the detection efficiency. We analyze the autocorrelations of shot noise and electronic noise and determine the optimal weight by solving a generalized Rayleigh quotient problem. The optimal weight enhances the squeezing and anti-squeezing levels observed experimentally. These results highlight the importance of optimized signal processing for efficient quantum measurements.
Low-noise, efficient, phase-sensitive time-domain optical detection is essential for foundational tests of quantum physics based on optical quantum states and the realization of numerous applications ranging from quantum key distribution to coherent classical telecommunications. Stability, bandwidth, efficiency, and signal-to-noise ratio are crucial performance parameters for effective detector operation. Here we present a high-bandwidth, low-noise, ultra-stable time-domain coherent measurement scheme based on balanced homodyne detection ideally suited to characterization of quantum and classical light fields in well-defined ultrashort optical pulse modes.
A balanced homodyne detection scheme with nanosecond time resolution and sub-shot-noise sensitivity has been developed and successfully tested yielding an efficient detection scheme for high-speed quantum-optical measurements and communication protocols, for example, quantum cryptography. The parameters of the detector and its precise balancing allow complete characterization of quantum states created by femtosecond light pulses that include the measurement of photon number, optical phase, and statistical properties with a high signal-to-noise ratio for the whole bandwidth from DC to several tens of megahertz. The electronic part of the detector is based on a commercially available amplifier that provides ease of construction and use while yielding good performance.
We design and experimentally characterize a balanced homodyne detector optimized for high-repetition-rate (100 MHz) pulsed optical sources. Unlike conventional transimpedance-amplifier architectures, which suffer from nonlinearities and dynamic instabilities with ultrashort pulses, our approach allows to directly amplify the photocurrent extracted at the common photodiode node without feedback loops. A theoretical model describing the detector response, noise, and pulse-to-pulse correlations is developed, providing quantitative predictions for the signal variance, signal-to-noise ratio (SNR), and inter-pulse correlations. Implemented with two matched InGaAs photodiodes illuminated by a 1030 nm mode-locked laser at 100 MHz, the detector exhibits excellent linearity and shot-noise-limited scaling of the signal variance with optical power. Optimizing the temporal integration window yields a maximum SNR of about 14 dB, while correlation measurements confirm negligible inter-pulse correlations. These results demonstrate that the proposed architecture offers a robust and simple solution for high-speed pulsed homodyne detection, suitable for quantum optics and continuous-variable quantum information applications.