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Photonics

High-Bandwidth Intensity-Difference Squeezed State at 895 nm Based on Four-Wave Mixing

Rong Ma, Wen Zhang, Xiaowei Wu, Xiaoqin Qu, Xiaolong Su

Published Oct 30, 2025• 3 citations
Publisher

Abstract

As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by the bandwidth of photodetectors, broadband intensity-difference squeezed state based on this system has not yet been reported. Here, we developed a transimpedance broadband balanced homodyne detector at 895 nm, achieving a bandwidth greater than 100 MHz and a maximum signal-to-noise ratio of 15 dB with 4 mW optical power. Utilizing this detector in a nondegenerate FWM process based on cesium vapor, we experimentally achieved broadband intensity-difference squeezing with a bandwidth of 100 MHz, which yielded a maximum squeezing of −7.17 ± 0.8 dB between 20 and 40 MHz. Meanwhile, using this detector, we experimentally investigated the cavity-enhanced FWM process, achieving a squeezing level of −6.07 ± 0.5 dB within a 4 MHz frequency range, which is limited by the cavity bandwidth. This work provides a reliable detection tool and experimental foundation for the research and application of broadband squeezed light sources based on FWM.

DOI
10.3390/photonics12111073

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As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by the bandwidth of photodetectors, broadband intensity-difference squeezed state based on this system has not yet been reported. Here, we developed a transimpedance broadband balanced homodyne detector at 895 nm, achieving a bandwidth greater than 100 MHz and a maximum signal-to-noise ratio of 15 dB with 4 mW optical power. Utilizing this detector in a nondegenerate FWM process based on cesium vapor, we experimentally achieved broadband intensity-difference squeezing with a bandwidth of 100 MHz, which yielded a maximum squeezing of −7.17 ± 0.8 dB between 20 and 40 MHz. Meanwhile, using this detector, we experimentally investigated the cavity-enhanced FWM process, achieving a squeezing level of −6.07 ± 0.5 dB within a 4 MHz frequency range, which is limited by the cavity bandwidth. This work provides a reliable detection tool and experimental foundation for the research and application of broadband squeezed light sources based on FWM.
Squeezing-based quantum metrology has been extensively applied in the field of precision measurement. Performance characteristics of squeezed light are obtained by a balanced homodyne detector. Here, we report a large dynamic range balanced homodyne detector with low-noise and high-signal-to-noise-ratio (SNR) for broadband squeezed light measurement. We perform a comprehensive theoretical analysis of the SNR in a wide bandwidth and experimentally analyze the important printed circuit board (PCB) layout and electronic components. Consequently, in the 100 MHz frequency band, the SNR and common mode rejection ratio (CMRR) rise over 12.6 dB and 55 dB, respectively, and the electronic noise is suppressed below -90 dB. The directly observed squeezing level at 1550 nm with the specified detector is 11.8 dB at 2 MHz and 3.1 dB at 100 MHz.
We experimentally demonstrate the creation of two correlated beams generated by a nondegenerate four-wave-mixing amplifier at λ=795 nm in hot rubidium vapor. We achieve intensity difference squeezing at frequencies as low as 1.5 kHz which is so far the lowest frequency to observe squeezing in an atomic system. The squeezing spans from 5.5 to 16.5 MHz with a maximum squeezing of -5 dB at 1 MHz. We can control the squeezing bandwidth by changing the pump power. Both low frequency and controllable bandwidth squeezing show great potential in sensitivity detection and precise control of the atom optics measurement.
Quantum correlated states of light, such as squeezed states, are a fundamental resource for the development of quantum technologies, as they are needed for applications in quantum metrology, quantum computation, and quantum communications. It is thus critical to develop compact, efficient, and robust sources to generate such states. Here, we report on a compact, narrowband, fiber-coupled source of two-mode squeezed states of light at 795 nm based on four-wave mixing (FWM) in an 85Rb atomic vapor. The source is designed in a small modular form factor, with two input fiber-coupled beams, the seed and pump beams required for the FWM, and two output fibers, one for each of the modes of the squeezed state. The system is optimized for low pump power (135 mW) to achieve a maximum intensity-difference squeezing of 4.4 dB after the output of fibers at an analysis frequency of 1 MHz. The narrowband nature of the source makes it ideal for atomic-based quantum sensing and quantum networking configurations that rely on atomic quantum memories. Such a source paves the way for a versatile and portable platform for applications in quantum information science.
Abstract Squeezed states of light, generated through four-wave mixing (FWM), are increasingly recognized as valuable resources for various applications in quantum sensing, quantum imaging, and quantum information processing. In this study, we report achieving more than − 7.8 dB of intensity-difference squeezing (IDS) in two-mode squeezed states from hot 85Rb vapor and − 5.0 dB from hot 87Rb vapor, utilizing a fiber electro-optic modulator (EOM) within a single home-made diode laser system. By mitigating the effects of undesired multimode from the EOM on the squeezing, we experimentally demonstrated the IDS of 85Rb and 87Rb atoms within a single experimental setup, benefiting from the EOM's ability to provide higher frequency shifts. This advancement may expand the scope of applications for hot atomic-vapor-based quantum technologies, leveraging the capabilities of the EOM.
Squeezed light plays a crucial role in state-of-the-art quantum metrology and quantum information experiments. There is significant interest in utilizing squeezed states at high MHz and GHz frequencies. However, past efforts to build suitable photodetectors at these frequencies have yet to yield the required high quantum efficiency. Here, we present the development of a high-frequency balanced photodetector with near-unity quantum efficiency, realized with off-the-shelf components. The detector operates in balanced mode up to approximately 500 MHz, above which the differential frequency response limits its performance. To obtain high sensitivity above 500 MHz, the detector can be efficiently used in an unbalanced homodyne detection scheme. We employ our detector in this unbalanced mode to measure a squeezing comb up to 6.4 GHz, achieving a squeezing level of up to 10.7 dB. By sharing our experience, specifically in identifying the unequal frequency response as a limiting factor, we aim to enable and advance further developments in the field.
Squeezed light plays a crucial role in state-of-the-art quantum metrology and quantum information experiments. There is significant interest in utilizing squeezed states at high MHz and GHz frequencies. However, past efforts to build suitable photodetectors at these frequencies have yet to yield the required high quantum efficiency. Here, we present the development of a high-frequency balanced photodetector with near-unity quantum efficiency, realized with off-the-shelf components. The detector operates in balanced mode up to approximately 500 MHz, above which the differential frequency response limits its performance. To obtain high sensitivity above 500 MHz, the detector can be efficiently used in an unbalanced homodyne detection scheme. We employ our detector in this unbalanced mode to measure a squeezing comb up to 6.4 GHz, achieving a squeezing level of up to 10.7 dB. By sharing our experience, specifically in identifying the unequal frequency response as a limiting factor, we aim to enable and advance further developments in the field.