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arXiv:2504.00627 · Light Science & Applications

Bright squeezed light in the kilohertz frequency band

Ruixin Li, Bingnan An, Nanjing Jiao, Junyang Liu, Lirong Chen, Yajun Wang, Yaohui Zheng

Published Sep 8, 2025• 20 citations
arXivHTMLPDF

Abstract

The dominant technical noise of a free-running laser practically limits bright squeezed light generation, particularly within the MHz band. To overcome this, we develop a comprehensive theoretical model for nonclassical power stabilization, and propose a novel bright squeezed light generation scheme incorporating hybrid power noise suppression. Our approach integrates broadband passive power stabilization with nonclassical active stabilization, extending the feedback bandwidth to MHz frequencies. This hybrid technique achieves an additional 9 dB technical noise suppression, establishing critical prerequisites for broadband bright squeezed light generation. Finally, a -5.5 dB bright squeezed light at 1 mW with kHz-MHz squeezing bandwidth was generated. The experimental results show excellent agreement with theoretical predictions, which represent we have comprehensively demonstrated a milliwatt-order bright squeezed light across kHz-MHz frequencies. Our work enables new quantum metrology applications and paves the way for next-generation quantum-enhanced technologies. Nonclassical hybrid passive-active power stabilization enables milliwatt-level bright squeezing across kHz-MHz band.

DOI
10.1038/s41377-025-02013-7

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Acta Physica Sinica•Jan 1, 2025•1 citation
The dominant technical noise of a free-running laser practically limits bright squeezed light generation, particularly within the MHz band. To overcome this, we develop a comprehensive theoretical model for nonclassical power stabilization, and propose a novel bright squeezed light generation scheme incorporating hybrid power noise suppression. Our approach integrates broadband passive power stabilization with nonclassical active stabilization, extending the feedback bandwidth to MHz frequencies. This hybrid technique achieves an additional 9 dB technical noise suppression, establishing critical prerequisites for broadband bright squeezed light generation. Finally, a -5.5 dB bright squeezed light at 1 mW with kHz-MHz squeezing bandwidth was generated. The experimental results show excellent agreement with theoretical predictions, which represent we have comprehensively demonstrated a milliwatt-order bright squeezed light across kHz-MHz frequencies. Our work enables new quantum metrology applications and paves the way for next-generation quantum-enhanced technologies. Nonclassical hybrid passive-active power stabilization enables milliwatt-level bright squeezing across kHz-MHz band.
Low-power-noise lasers are essential for many high-precision experiments. Shot noise imposes a fundamental limit on the power stability achievable with classical light sources. In this Letter, we report the generation of bright squeezed light in the audio band, which can improve the sensitivity of otherwise shot-noise-limited measurements. The bright squeezed light source is experimentally realized via the use of squeezed vacuum in a power stabilization scheme. We demonstrate a laser beam at a power of 9.9 mW with a broadband power noise suppression below the classical stabilization limit by up to 8 . 7 − 0.4 + 0.3 dB in the audio band, resulting in a bright squeezed beam with a power noise of 5 . 7 − 0.4 + 0.3 dB below shot noise for frequencies from 6 kHz to 20 kHz. We further conceptually outline a method to surpass this result in the future.
An extremely conspicuous passive power noise stabilization is the first, to the best of our knowledge, discovered in a cavity-enhanced second-harmonic generation (SHG) process. Differing from the SHG as a buffer reservoir, the stronger strength of the nonlinear interaction pushes the power noise suppression level to a higher value and exhibits a broadband noise reduction performance due to the mechanism of dynamic pump suppression in the SHG process. The noise is suppressed to near shot noise limit (SNL) among the kHz to MHz frequency range, accompanied by a maximum noise reduction of 35 dB. A comprehensive demonstration indicates that the nonlinear interaction has no function on the phase noise of fundamental and harmonic waves. A theoretical model is also established that is consistent well with the experimental results. The methodology is beneficial to multiple optical metrology experiments.
We present the generation of nonclassical state using an amplified diode laser as a light source. The intensity noise of an amplified diode laser was significantly suppressed and reached the shot noise limit at 15 MHz using both a filter cavity and resonant optical feedback. Frequency doubling efficiency of 66% and up to 120 mW output power of green has been achieved in cw second-harmonic generation from 1080 nm to 540 nm. Bright two-mode amplitude-squeezed state was generated from a type-II nondegenerate optical parametric amplifier pumped by generated green light. The measured noise reduction is 2.1+/-0.2 dB below the shot-noise level.
Pump power fluctuations are a critical factor in limiting the long-term stability of quantum sensing light sources. However, existing laser power stabilization techniques fail to efficiently address power fluctuations caused by downstream beam-pointing noise coupling. Here, we propose an optimized suppression scheme of pump power fluctuations that integrates a passive second harmonic process and active feedback control, achieving multiple noise suppression of both pointing and intensity noise in the pump field. Within the measurement time of 8.5 hours, we achieve a quantum sensing light source with a squeezing factor of 10.0 dB and its fluctuations below 0.4 dB. The proposed approach effectively boosts the long-term stability of the quantum squeezing source, thus paving a solid way for expanding the utilization of squeezing sources within the realm of quantum precision measurement.
High levels of laser power stability are necessary for high precision metrology applications. The classical limit for the achievable power stability is determined by the shot noise of the light used to generate a power control signal. Increasing the power of the detected light reduces the relative shot noise level and allows higher stabilities. However, sufficiently high power is not always available and the detection of high laser powers is challenging. Here, we demonstrate a nonclassical way to improve the achievable power stability without increasing the detected power. By the injection of a squeezed vacuum field of light we improve the classical laser power stability beyond its shot noise limit by 9.4_{-0.6}^{+0.6} dB at Fourier frequencies between 5 and 80 kHz. For only 90.6 μA of detected photocurrent we achieve a relative laser power noise of 2.0_{-0.1}^{+0.1}×10^{-8}/sqrt[Hz]. This is the first demonstration of a squeezed light-enhanced laser power stabilization and its performance is equivalent to an almost tenfold increase of detected laser power in a classical scheme. The analysis reveals that the technique presented here has the potential to achieve stability levels of 4.2×10^{-10}/sqrt[Hz] with 58 mA photocurrent measured on a single photodetector.
This research focuses on advanced noise suppression technologies for high-precision measurement systems, particularly addressing the limitations of classical noise reducing approaches. The noise level of laser sources is a crucial factor that directly affects the measurement sensitivity in applications such as gravitational wave detection and biomedical imaging. Classical feedback control technologies are effective but often encounter a bottleneck resulting from the classical noise suppression limits. To cope with these challenges, a novel method integrating quantum squeezed light with classical feedback control systems to reduce intensity noise is proposed in this work. By employing an amplitude-squeezed light field, a quantum-enhanced feedback control model is developed, thereby theoretically examining the influence of both the feedback loop gain and the degree of squeezing on the noise suppression performance. The results show that the injection of squeezed light significantly reduces the intensity noise, approaching the shot noise limit (SNL), thereby improving the system sensitivity beyond the classical noise reduction boundaries. Specifically, –10 dB squeezed state injection into the feedback system yields an additional noise suppression of approximately 8.97 dB, exceeding what is achievable using classical feedback alone. This demonstrates that the potential of the proposed method can enhance measurement precision close to the quantum noise limits without increasing the laser power. The analysis highlights the asymmetric noise suppression effects between the inner feedback loop and outer feedback loop. Although the outer loop benefits significantly from the squeezed light injection and achieves noise levels that are unattainable by classical feedback methods, the inner loop shows relatively minor improvements. This asymmetry is attributed to the inherent characteristics of quantum squeezing and the limitations of the feedback loop design. Further investigation into the individual noise components reveals that the primary contributors to the intensity noise include input noise, photodetector noise, and beam splitter-induced vacuum fluctuations. The injection of squeezed light effectively mitigates these vacuum fluctuations, which are typically a major noise source in high-precision laser systems. Theoretical research results show that the use of squeezed light in feedback control systems can effectively enhance noise suppression, equivalent to a nine fold increase in detected optical power, without the physical drawbacks of increasing laser power such as thermal noise. In conclusion, this study provides a theoretical validation of combining quantum squeezed states with classical feedback control to exceed classical noise suppression limits. The integration of a –10 dB squeezed state demonstrates a significant noise reduction, showing that this hybrid approach could revolutionize noise management in precision measurement applications. The results pave the way for further exploring quantum-enhanced control technologies in fields such as gravitational wave detection, quantum communication, and advanced optical sensing, providing a pathway for improving sensitivity and noise suppression without increasing additional power requirements.