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

arXiv:2108.01242 · Advanced Quantum Technologies

Magneto‐Optical Sensing Beyond the Shot Noise Limit

Yun‐Yi Pai, Claire E. Marvinney, Chengyun Hua, Raphael C. Pooser, Benjamin J. Lawrie

Published Nov 12, 2021• 7 citations
arXivHTMLPDF

Abstract

Abstract Magneto‐optical sensors including spin noise spectroscopies and magneto‐optical Kerr effect microscopies are now ubiquitous tools for materials characterization that can provide new understanding of spin dynamics, hyperfine interactions, spin‐orbit interactions, and charge‐carrier g‐factors. Both interferometric and intensity‐difference measurements can provide photon‐shot‐noise‐limited sensitivity, but further improvements in sensitivity with classical resources require either increased laser power that can induce unwanted heating and electronic perturbations or increased measurement times that can obscure out‐of‐equilibrium dynamics and slow experimental throughput. Proof‐of‐principle measurements have already demonstrated quantum enhanced spin noise measurements with a squeezed readout field that are likely to be critical to the nonperturbative characterization of spin excitations in quantum materials that emerge at low temperatures. Here, a truncated nonlinear interferometric readout for low‐temperature magneto‐optical Kerr effect and related magneto‐optical microscopies that is accessible with today's quantum optical resources is proposed. 10 sensitivity is achievable with optical power as small as 1 µW. As a result, measurements may be performed at temperatures as low as 83 mK in commercially available dilution refrigerators. This combination of high sensitivity and low operating temperature is impossible to achieve with any classical measurement. The quantum advantage for the proposed measurements persists even in the limit of large loss and small squeezing parameters.

DOI
10.1002/qute.202100107

Related papers

Quantum Enhanced Probes of Magnetic Circular Dichroism

Chengyun Hua, Claire E. Marvinney, Seongjin Hong +7 more

Abstract Magneto‐optical microscopies, including optical measurements of magnetic circular dichroism, are increasingly ubiquitous tools for probing spin‐orbit coupling, charge‐carrier g‐factors, and chiral excitations in matter, but the minimum detectable signal in classical magnetic circular dichroism measurements is fundamentally limited by the shot‐noise limit of the optical readout field. Here, a two‐mode squeezed light source is used to improve the minimum detectable signal in magnetic circular dichroism measurements by 3 decibels compared with state‐of‐the‐art classical measurements, even with relatively lossy samples like terbium gallium garnet. These results provide a framework for new quantum‐enhanced magneto‐optical microscopies that are particularly critical for environmentally sensitive materials and for low temperature measurements where increased optical power can introduce unacceptable thermal perturbations.

arXiv:2305.02904•Advanced Quantum Technologies•Sep 19, 2023•7 citations

Quantum Nonlinear Spectroscopy via Correlations of Weak Faraday‐Rotation Measurements

Brian Chung Hang Cheung, Ren‐Bao Liu

Abstract The correlations of fluctuations are key to studying fundamental quantum physics and quantum many‐body dynamics. They are also useful information for understanding and combating decoherence in quantum technology. Nonlinear spectroscopy and noise spectroscopy are powerful tools to characterize fluctuations, but they can access only very few among the many types of higher‐order correlations. A systematic quantum sensing approach, called quantum nonlinear spectroscopy (QNS), is recently proposed for extracting arbitrary types and orders of time‐ordered correlations, using sequential weak measurement via a spin quantum sensor. However, the requirement of a central spin as the quantum sensor limits the versatility of the QNS since usually a central spin interacts only with a small number of particles in proximity and the measurement of single spins needs stringent conditions. Here, the aim is to employ the polarization (a pseudo‐spin) of a coherent light beam as a quantum sensor for QNS. After interacting with a target system (such as a transparent magnetic material), the small Faraday rotation of the linearly polarized light can be measured, which constitutes a weak measurement of the magnetization in the target system. Using a Mach–Zehnder interferometer with a designed phase shift, one can post‐select the effects of the light–material interaction to be either a quantum evolution or a quantum measurement of the material magnetization. This way, the correlated difference photon counts of a certain number of measurement shots, each with a designated interference phase, can be made proportional to a certain type and order of correlations of the magnetic fluctuations in the material. The analysis of the signal‐to‐noise ratios shows that the second‐order correlations are detectable in general under realistic conditions and higher‐order correlations are significant when the correlation lengths of the fluctuations are comparable to the laser spot size (such as in systems near the critical points). Since the photon sensor can interact simultaneously with many particles and interferometry is a standard technique, this protocol of QNS is advantageous for studying quantum many‐body systems.

arXiv:2309.00207•Advanced Quantum Technologies•Jun 16, 2024•3 citations

Optical phase measurement beyond the shot noise limit using optical spin squeezed state

Takafumi Ono

Quantum metrology enables us to estimate optical phase shifts beyond the shot noise limit. Applications include quantum-enhanced biological measurement [1], microscopy [2] and gravitational wave detection[3]. For two-mode N-photon system, the NOON state can achieve the highest possible phase sensitivity where multi-photon coherence between two states significantly contributes to improving the phase sensitivity. Another alternative approach to improve the phase sensitivity by use of squeezed states. Squeezing is usually characterized by reducing the quantum noise of desired observable at the expense of increasing the quantum noise for its non-commute partner. Because shot-noise limits the phase sensitivity of any classical states, the reduced quantum noise can be used for improving the phase sensitivity. Here we experimentally study the phase sensitivity of an optical spin-squeezed state by using linear optics. We generated the optical spin-squeezed state using one photon subtraction from a down converted photon source. To implement the sub-shot noise measurement, we used multiplexed photon number resolving detectors so that we can reconstruct the photon number statistics of the state. In the talk, we will analyse the generated state in terms of both squeezing and phase sensitivity by using Fisher information.

•Jan 1, 2016•0 citations

Quantum Sensing with Squeezed Light

Benjamin J. Lawrie, Paul D. Lett, Alberto M. Marino +1 more

The minimum resolvable signal in sensing and metrology platforms that rely on optical readout fields is increasingly constrained by the standard quantum limit, which is determined by the sum of photon shot noise and back-action noise. A combination of back-action and shot noise reduction techniques will be critical to the development of the next generation of sensors for applications ranging from high-energy physics to biochemistry and for novel microscopy platforms capable of resolving material properties that were previously obscured by quantum noise. This Perspective reviews the dramatic advances made in the use of squeezed light for sub-shot-noise quantum sensing in recent years and highlights emerging applications that enable new science based on signals that would otherwise be obscured by noise at the standard quantum limit.

ACS Photonics•May 13, 2019•337 citations

Quantum Weak Force Sensor with Cross‐Kerr Nonlinearity and Parametric Amplification

Yingjian Zhu, Xue Yan Han, Hong‐Fu Wang +1 more

ABSTRACT The sensitivity of optomechanical sensors is fundamentally constrained by the combined effects of shot noise and quantum back‐action. Here we show that the joint action of cross‐Kerr nonlinearity and an optical parametric amplifier (OPA) can effectively suppress these noises. By tailoring the cross‐Kerr strength, the force‐sensing sensitivity can surpass the standard quantum limit (SQL), while an optimal driving power broadens the detection bandwidth. We further find that the system becomes unstable when the detuning falls below . Importantly, the inclusion of an OPA enhances robustness against thermal fluctuations, allowing the sensitivity of force measurement to surpass the SQL even at temperatures up to 300 K. A detailed noise analysis reveals that cross‐Kerr nonlinearity predominantly suppresses back‐action noise, whereas the OPA provides a strong reduction of shot noise. These results establish a promising hybrid strategy for realizing optomechanical sensors that combine high sensitivity with thermal resilience, with broad applications ranging from medical diagnostics to gravitational‐wave astronomy.

Advanced Quantum Technologies•Dec 9, 2025•0 citations

Squeezed-light enhancement of sensitivity and signal bandwidth in an optically-pumped magnetometer

Charikleia Troullinou, Ricardo Jiménez-Martínez, Jia Kong +2 more

We study the effect of optical squeezing on the performance of a sensitive, quantum-noise-limited optically-pumped magnetometer. We use Bell-Bloom optical pumping to excite a $^{87}$Rb vapor and Faraday rotation to detect spin precession. The sub-$\mathrm{pT}/\sqrt{\mathrm{Hz}}$ sensitivity is limited by spin projection noise (photon shot noise) at low (high) frequencies. Probe polarization squeezing both improves high-frequency sensitivity and increases signal bandwidth. The accompanying polarization anti-squeezing perturbs only an unmeasured spin component, so there is no loss of sensitivity at any frequency. The method is compatible with high-density and multi-pass techniques that reach extreme sensitivity.

•Aug 3, 2021•0 citations
Abstract Magneto‐optical sensors including spin noise spectroscopies and magneto‐optical Kerr effect microscopies are now ubiquitous tools for materials characterization that can provide new understanding of spin dynamics, hyperfine interactions, spin‐orbit interactions, and charge‐carrier g‐factors. Both interferometric and intensity‐difference measurements can provide photon‐shot‐noise‐limited sensitivity, but further improvements in sensitivity with classical resources require either increased laser power that can induce unwanted heating and electronic perturbations or increased measurement times that can obscure out‐of‐equilibrium dynamics and slow experimental throughput. Proof‐of‐principle measurements have already demonstrated quantum enhanced spin noise measurements with a squeezed readout field that are likely to be critical to the nonperturbative characterization of spin excitations in quantum materials that emerge at low temperatures. Here, a truncated nonlinear interferometric readout for low‐temperature magneto‐optical Kerr effect and related magneto‐optical microscopies that is accessible with today's quantum optical resources is proposed. 10 sensitivity is achievable with optical power as small as 1 µW. As a result, measurements may be performed at temperatures as low as 83 mK in commercially available dilution refrigerators. This combination of high sensitivity and low operating temperature is impossible to achieve with any classical measurement. The quantum advantage for the proposed measurements persists even in the limit of large loss and small squeezing parameters.
Abstract Magneto‐optical microscopies, including optical measurements of magnetic circular dichroism, are increasingly ubiquitous tools for probing spin‐orbit coupling, charge‐carrier g‐factors, and chiral excitations in matter, but the minimum detectable signal in classical magnetic circular dichroism measurements is fundamentally limited by the shot‐noise limit of the optical readout field. Here, a two‐mode squeezed light source is used to improve the minimum detectable signal in magnetic circular dichroism measurements by 3 decibels compared with state‐of‐the‐art classical measurements, even with relatively lossy samples like terbium gallium garnet. These results provide a framework for new quantum‐enhanced magneto‐optical microscopies that are particularly critical for environmentally sensitive materials and for low temperature measurements where increased optical power can introduce unacceptable thermal perturbations.
Abstract The correlations of fluctuations are key to studying fundamental quantum physics and quantum many‐body dynamics. They are also useful information for understanding and combating decoherence in quantum technology. Nonlinear spectroscopy and noise spectroscopy are powerful tools to characterize fluctuations, but they can access only very few among the many types of higher‐order correlations. A systematic quantum sensing approach, called quantum nonlinear spectroscopy (QNS), is recently proposed for extracting arbitrary types and orders of time‐ordered correlations, using sequential weak measurement via a spin quantum sensor. However, the requirement of a central spin as the quantum sensor limits the versatility of the QNS since usually a central spin interacts only with a small number of particles in proximity and the measurement of single spins needs stringent conditions. Here, the aim is to employ the polarization (a pseudo‐spin) of a coherent light beam as a quantum sensor for QNS. After interacting with a target system (such as a transparent magnetic material), the small Faraday rotation of the linearly polarized light can be measured, which constitutes a weak measurement of the magnetization in the target system. Using a Mach–Zehnder interferometer with a designed phase shift, one can post‐select the effects of the light–material interaction to be either a quantum evolution or a quantum measurement of the material magnetization. This way, the correlated difference photon counts of a certain number of measurement shots, each with a designated interference phase, can be made proportional to a certain type and order of correlations of the magnetic fluctuations in the material. The analysis of the signal‐to‐noise ratios shows that the second‐order correlations are detectable in general under realistic conditions and higher‐order correlations are significant when the correlation lengths of the fluctuations are comparable to the laser spot size (such as in systems near the critical points). Since the photon sensor can interact simultaneously with many particles and interferometry is a standard technique, this protocol of QNS is advantageous for studying quantum many‐body systems.
Quantum metrology enables us to estimate optical phase shifts beyond the shot noise limit. Applications include quantum-enhanced biological measurement [1], microscopy [2] and gravitational wave detection[3]. For two-mode N-photon system, the NOON state can achieve the highest possible phase sensitivity where multi-photon coherence between two states significantly contributes to improving the phase sensitivity. Another alternative approach to improve the phase sensitivity by use of squeezed states. Squeezing is usually characterized by reducing the quantum noise of desired observable at the expense of increasing the quantum noise for its non-commute partner. Because shot-noise limits the phase sensitivity of any classical states, the reduced quantum noise can be used for improving the phase sensitivity. Here we experimentally study the phase sensitivity of an optical spin-squeezed state by using linear optics. We generated the optical spin-squeezed state using one photon subtraction from a down converted photon source. To implement the sub-shot noise measurement, we used multiplexed photon number resolving detectors so that we can reconstruct the photon number statistics of the state. In the talk, we will analyse the generated state in terms of both squeezing and phase sensitivity by using Fisher information.
The minimum resolvable signal in sensing and metrology platforms that rely on optical readout fields is increasingly constrained by the standard quantum limit, which is determined by the sum of photon shot noise and back-action noise. A combination of back-action and shot noise reduction techniques will be critical to the development of the next generation of sensors for applications ranging from high-energy physics to biochemistry and for novel microscopy platforms capable of resolving material properties that were previously obscured by quantum noise. This Perspective reviews the dramatic advances made in the use of squeezed light for sub-shot-noise quantum sensing in recent years and highlights emerging applications that enable new science based on signals that would otherwise be obscured by noise at the standard quantum limit.
ABSTRACT The sensitivity of optomechanical sensors is fundamentally constrained by the combined effects of shot noise and quantum back‐action. Here we show that the joint action of cross‐Kerr nonlinearity and an optical parametric amplifier (OPA) can effectively suppress these noises. By tailoring the cross‐Kerr strength, the force‐sensing sensitivity can surpass the standard quantum limit (SQL), while an optimal driving power broadens the detection bandwidth. We further find that the system becomes unstable when the detuning falls below . Importantly, the inclusion of an OPA enhances robustness against thermal fluctuations, allowing the sensitivity of force measurement to surpass the SQL even at temperatures up to 300 K. A detailed noise analysis reveals that cross‐Kerr nonlinearity predominantly suppresses back‐action noise, whereas the OPA provides a strong reduction of shot noise. These results establish a promising hybrid strategy for realizing optomechanical sensors that combine high sensitivity with thermal resilience, with broad applications ranging from medical diagnostics to gravitational‐wave astronomy.
We study the effect of optical squeezing on the performance of a sensitive, quantum-noise-limited optically-pumped magnetometer. We use Bell-Bloom optical pumping to excite a 87^{87}87Rb vapor and Faraday rotation to detect spin precession. The sub-pT/Hz\mathrm{pT}/\sqrt{\mathrm{Hz}}pT/Hz​ sensitivity is limited by spin projection noise (photon shot noise) at low (high) frequencies. Probe polarization squeezing both improves high-frequency sensitivity and increases signal bandwidth. The accompanying polarization anti-squeezing perturbs only an unmeasured spin component, so there is no loss of sensitivity at any frequency. The method is compatible with high-density and multi-pass techniques that reach extreme sensitivity.