Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Observation of Quantum Advantage with Squeezed Light for Absorption Measurement

Fu Li, Tian T. Li, Marlan O. Scully, G. S. Agarwal

Published Jul 10, 2020• 1 citation
OpenAlex

Abstract

Absorption measurements are routinely used in science and engineering, it is an exceptionally versatile tool for most applications. For absorption measurements using laser beams of light, the sensitivity is theoretically limited by the shot noise due to the fundamental Poisson distribution of photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use bright squeezed light to demonstrate direct absorption measurement can be performed with sensitivity beyond the shot-noise limit. We present a practically realizable scheme, where the bright squeezed light is in the continuous-variable regime generated by the four-wave mixing process in an atomic rubidium vapor. This is a direct sub-shot-noise measurement of absorption, and more than 1 dB quantum advantage for the measurement sensitivity is demonstrated at faint absorption levels. A theoretical model that yields excellent agreements with experimental observations is also provided.

Related papers

Quantum Advantage with Seeded Squeezed Light for Absorption Measurement

Fu Li, Tian Li, Marlan O. Scully +1 more

Absorption measurement is an exceptionally versatile tool for many applications in science and engineering. For absorption measurements using laser beams of light, the sensitivity is theoretically limited by the shot noise due to the fundamental Poisson distribution of the photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use seeded squeezed light to demonstrate that direct-absorption measurements can be performed with a sensitivity beyond the shot-noise limit. We present a practically realizable scheme, where intensity-squeezed beams are generated by a seeded four-wave mixing process in an atomic rubidium-vapor cell. More than 1.2 dB quantum advantage for the measurement sensitivity is obtained at faint absorption levels ($\ensuremath{\le}10\mathrm{%}$). We also present a detailed theoretical analysis to show that the observed quantum advantage when corrected for optical loss would be equivalent to 3 dB. Our experiment demonstrates a direct sub-shot-noise measurement of absorption that requires neither homodyne or lock-in nor logic coincidence-detection schemes. It is therefore very applicable in many circumstances where sub-shot-noise-level absorption measurements are highly desirable.

arXiv:2007.05583•Physical Review Applied•Apr 20, 2021•33 citations

Quantum advantage of seeded, squeezed light in absorption and gain measurement

G. S. Agarwal

We use bright squeezed light to demonstrate that direct absorption and gain measurements can be performed with sensitivity beyond the shot-noise limit without requiring homodyne/lock-in, or logic coincidence detection schemes. Previously we reported more than 1 dB quantum advantage [ 3 dB when corrected losses in optical paths] for the measurement sensitivity at faint absorption levels. We present our detailed results on definite quantum advantage of about 3dB in measurements of Brillouin gain.

Optical and Quantum Sensing and Precision Metrology II•Mar 9, 2022•0 citations

Sub-shot-noise Rydberg EIT spectrum

Hongmei Yan, Mingyong Jing, Yanjie Tong +8 more

Abstract Atom-based sensing with optical readout is fundamentally limited by photon shot noise. Squeezed light can effectively suppress this noise of optical readout, thereby enabling measurement sensitivities beyond the standard quantum limit, but their application in light–atom hybrid systems is often hindered by absorption losses of atomic medium. Here, we demonstrate the first realization of electromagnetically induced transparency spectrum in a Rydberg-atom system using a squeezed probe field that surpasses the photon shot noise limit. Our theoretical model identifies atomic transit and absorption-induced losses as the primary factors limiting squeezing preservation. Experimentally, we engineer the atomic ensemble as a medium with tunable transmittance by employing Doppler-matched velocity-selective excitation to suppress absorption, achieving a squeezing transmission of 90.4 $$\%$$ % for -1.7 dB squeezed light through a cesium vapor cell. This work is a critical step towards quantum-enhanced Rydberg atom sensors.

PhotoniX•Dec 15, 2025•5 citations

Absorption spectroscopy at the ultimate quantum limit from single-photon states

Rebecca Whittaker, Chris Erven, Alex Neville +4 more

Absorption spectroscopy is routinely used to characterise chemical and biological samples. For the state-of-the-art in laser absorption spectroscopy, precision is theoretically limited by shot-noise due to the fundamental Poisson-distribution of photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use wavelength-correlated and tuneable photon pairs to demonstrate how absorption spectroscopy can be performed with precision beyond the shot-noise limit and near the ultimate quantum limit by using the optimal probe for absorption measurement—single photons. We present a practically realisable scheme, which we characterise both the precision and accuracy of by measuring the response of a control feature. We demonstrate that the technique can successfully probe liquid samples and using two spectrally similar types of haemoglobin we show that obtaining a given precision in resolution requires fewer heralded single probe photons compared to using an idealised laser.

arXiv:1508.00849•New Journal of Physics•Dec 21, 2016•93 citations

A Bright Squeezed Light Source for Quantum Sensing

Wenhai Yang, Wenting Diao, Chunxiao Cai +8 more

The use of optical sensing for in vivo applications is compelling, since it offers the advantages of non-invasiveness, non-ionizing radiation, and real-time monitoring. However, the signal-to-noise ratio (SNR) of the optical signal deteriorates dramatically as the biological tissue increases. Although increasing laser power can improve the SNR, intense lasers can severely disturb biological processes and viability. Quantum sensing with bright squeezed light can make the measurement sensitivity break through the quantum noise limit under weak laser conditions. A bright squeezed light source is demonstrated to avoid the deterioration of SNR and biological damage, which integrates an external cavity frequency-doubled laser, a semi-monolithic standing cavity with periodically poled titanyl phosphate (PPKTP), and a balanced homodyne detector (BHD) assembled on a dedicated breadboard. With the rational design of the mechanical elements, the optical layout, and the feedback control equipment, a maximum non-classical noise reduction of −10.7 ± 0.2 dB is observed. The average squeeze of −10 ± 0.2 dB in continuous operation for 60 min is demonstrated. Finally, the intracavity loss of degenerate optical parametric amplifier (DOPA) and the initial bright squeezed light can be calculated to be 0.0021 and −15.5 ± 0.2 dB, respectively. Through the above experimental and theoretical analysis, the direction of improving bright squeeze level is pointed out.

Chemosensors•Dec 25, 2022•13 citations

Bright squeezed light generation via nonclassical power stabilization

Jasper R. Venneberg, H. Vahlbruch, Marina Trad Nery +1 more

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.

Physical Review Research•May 20, 2025•7 citations
Absorption measurements are routinely used in science and engineering, it is an exceptionally versatile tool for most applications. For absorption measurements using laser beams of light, the sensitivity is theoretically limited by the shot noise due to the fundamental Poisson distribution of photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use bright squeezed light to demonstrate direct absorption measurement can be performed with sensitivity beyond the shot-noise limit. We present a practically realizable scheme, where the bright squeezed light is in the continuous-variable regime generated by the four-wave mixing process in an atomic rubidium vapor. This is a direct sub-shot-noise measurement of absorption, and more than 1 dB quantum advantage for the measurement sensitivity is demonstrated at faint absorption levels. A theoretical model that yields excellent agreements with experimental observations is also provided.
Absorption measurement is an exceptionally versatile tool for many applications in science and engineering. For absorption measurements using laser beams of light, the sensitivity is theoretically limited by the shot noise due to the fundamental Poisson distribution of the photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use seeded squeezed light to demonstrate that direct-absorption measurements can be performed with a sensitivity beyond the shot-noise limit. We present a practically realizable scheme, where intensity-squeezed beams are generated by a seeded four-wave mixing process in an atomic rubidium-vapor cell. More than 1.2 dB quantum advantage for the measurement sensitivity is obtained at faint absorption levels ($\ensuremath{\le}10\mathrm{%}$). We also present a detailed theoretical analysis to show that the observed quantum advantage when corrected for optical loss would be equivalent to 3 dB. Our experiment demonstrates a direct sub-shot-noise measurement of absorption that requires neither homodyne or lock-in nor logic coincidence-detection schemes. It is therefore very applicable in many circumstances where sub-shot-noise-level absorption measurements are highly desirable.
Abstract Atom-based sensing with optical readout is fundamentally limited by photon shot noise. Squeezed light can effectively suppress this noise of optical readout, thereby enabling measurement sensitivities beyond the standard quantum limit, but their application in light–atom hybrid systems is often hindered by absorption losses of atomic medium. Here, we demonstrate the first realization of electromagnetically induced transparency spectrum in a Rydberg-atom system using a squeezed probe field that surpasses the photon shot noise limit. Our theoretical model identifies atomic transit and absorption-induced losses as the primary factors limiting squeezing preservation. Experimentally, we engineer the atomic ensemble as a medium with tunable transmittance by employing Doppler-matched velocity-selective excitation to suppress absorption, achieving a squeezing transmission of 90.4 %\%% % for -1.7 dB squeezed light through a cesium vapor cell. This work is a critical step towards quantum-enhanced Rydberg atom sensors.
Absorption spectroscopy is routinely used to characterise chemical and biological samples. For the state-of-the-art in laser absorption spectroscopy, precision is theoretically limited by shot-noise due to the fundamental Poisson-distribution of photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. Here, we use wavelength-correlated and tuneable photon pairs to demonstrate how absorption spectroscopy can be performed with precision beyond the shot-noise limit and near the ultimate quantum limit by using the optimal probe for absorption measurement—single photons. We present a practically realisable scheme, which we characterise both the precision and accuracy of by measuring the response of a control feature. We demonstrate that the technique can successfully probe liquid samples and using two spectrally similar types of haemoglobin we show that obtaining a given precision in resolution requires fewer heralded single probe photons compared to using an idealised laser.
The use of optical sensing for in vivo applications is compelling, since it offers the advantages of non-invasiveness, non-ionizing radiation, and real-time monitoring. However, the signal-to-noise ratio (SNR) of the optical signal deteriorates dramatically as the biological tissue increases. Although increasing laser power can improve the SNR, intense lasers can severely disturb biological processes and viability. Quantum sensing with bright squeezed light can make the measurement sensitivity break through the quantum noise limit under weak laser conditions. A bright squeezed light source is demonstrated to avoid the deterioration of SNR and biological damage, which integrates an external cavity frequency-doubled laser, a semi-monolithic standing cavity with periodically poled titanyl phosphate (PPKTP), and a balanced homodyne detector (BHD) assembled on a dedicated breadboard. With the rational design of the mechanical elements, the optical layout, and the feedback control equipment, a maximum non-classical noise reduction of −10.7 ± 0.2 dB is observed. The average squeeze of −10 ± 0.2 dB in continuous operation for 60 min is demonstrated. Finally, the intracavity loss of degenerate optical parametric amplifier (DOPA) and the initial bright squeezed light can be calculated to be 0.0021 and −15.5 ± 0.2 dB, respectively. Through the above experimental and theoretical analysis, the direction of improving bright squeeze level is pointed out.
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.