Quantum sensing and metrology is the application of non-classical resources to the measurement of physical quantities with precision or accuracy beyond that allowed by classical physics. For many years non-classical resources such as atomic energy quantization, Josephson Effect, and Quantum Hall Effect have been used to define the fundamental units of time, voltage, and resistance, respectively. In recent years non-classical resources such as quantum squeezing and entanglement have been exploited to expand the range of physical phenomena measured with unprecedented precision or accuracy. We summarize some of the recent research on advanced quantum sensing and metrology and discuss our analyses of photon-added coherent states (PACS) of light. These analyses take into account imperfect photon addition and detection processes and show that PACS enable beyond-classical signal-to-noise ratio for photon counting even in cases where the probability of intended photon addition is 80%. We also show that there remains undiscovered fundamental properties of PACS related to their production and implementation.
Quantum sensing and metrology is the application of non-classical resources to the measurement of physical quantities with precision or accuracy beyond that allowed by classical physics. For many years non-classical resources such as atomic energy quantization, Josephson Effect, and Quantum Hall Effect have been used to define the fundamental units of time, voltage, and resistance, respectively. In recent years non-classical resources such as quantum squeezing and entanglement have been exploited to expand the range of physical phenomena measured with unprecedented precision or accuracy. We summarize some of the recent research on advanced quantum sensing and metrology and discuss our analyses of photon-added coherent states (PACS) of light. These analyses take into account imperfect photon addition and detection processes and show that PACS enable beyond-classical signal-to-noise ratio for photon counting even in cases where the probability of intended photon addition is 80%. We also show that there remains undiscovered fundamental properties of PACS related to their production and implementation.
Quantum sensors and metrology harness quantum phenomena—such as superposition, entanglement, and squeezing—to achieve precision measurements beyond classical limits. This review presents an overview of the fundamental principles underlying quantum sensing, including quantum coherence, entanglement-assisted measurement, and quantum-enhanced interferometry. Various quantum sensor platforms are discussed, including atomic clocks, nitrogen-vacancy (NV) center magnetometers, superconducting quantum interference devices (SQUIDs), optomechanical sensors, and trapped-ion systems. We explore their operational mechanisms, performance metrics, and technological implementations. Comparative analyses highlight sensitivity, spatial resolution, bandwidth, and environmental robustness. Advances in materials, control techniques, and hybrid architectures are examined, and emerging applications in navigation, geophysics, medical imaging, and fundamental physics are reviewed. Finally, future prospects for scalable and robust quantum metrology are discussed.
Quantum states of light, such as squeezed states or entangled states, can be used to make measurements (metrology), produce images, and sense objects with a precision that far exceeds what is possible classically, and also exceeds what was once thought to be possible quantum mechanically. The primary idea is to exploit quantum effects to beat the shot-noise limit in metrology and the Rayleigh diffraction limit in imaging and sensing. Quantum optical metrology has received a boost in recent years with an influx of ideas from the rapidly evolving field of optical quantum information processing. Both areas of research exploit the creation and manipulation of quantum-entangled states of light. We will review some of the recent theoretical and experimental advances in this exciting new field of quantum optical metrology, focusing on examples that exploit a particular two-mode entangled photon state – the High-N00N state.
ABSTRACT Weak measurement has emerged as a pivotal technique in precision metrology, utilizing unique amplification effects to enhance the capabilities of quantum sensing and quantum imaging. Quantum sensing can provide systems with unprecedented accuracy and sensitivity by utilizing its quantum properties. Quantum imaging uses entangled photon states to capture information, enabling signal‐to‐noise ratio and resolution that surpass the limits of classical imaging. The synergistic integration of weak measurement with quantum sensing and imaging paves the way for next‐generation technologies with practical value, significantly advancing frontiers of precision metrology and imaging science. This review elucidates the fundamental theory of weak value amplification and comprehensively discusses the performance of weak measurement strategies in quantum sensing and imaging frameworks, highlighting both classical techniques and emerging quantum applications. It covers four main directions: nanostructure, 2D atomic crystal, biochemistry, and optical imaging, including from structural parameters characterization to chemical reaction sensing to nonlocal weak measurement microscopy. This work aims to discuss recent advances in weak measurement applications for quantum sensing and imaging platforms, while outlining future development opportunities arising from the convergence of these three fields.
This paper explores the potential of quantum metrology, specifically utilizing entangled photon pairs, to significantly enhance the precision of measurement systems. Traditional metrology is often limited by the fundamental precision constraints imposed by classical physics. Entanglement, a quantum mechanical phenomenon where two or more particles are linked in such a way that they share the same fate, regardless of the distance separating them, offers a pathway to overcome these limitations. This work details the theoretical framework for employing entangled photon pairs to minimize measurement noise and improve sensor accuracy. The core claim is that leveraging these correlations can provide a measurable advantage over classical techniques. The proposed mechanism focuses on reducing uncertainties associated with the measurement process by exploiting the inherent correlations between the entangled photons. The research targets applications like gravitational wave detection and biological imaging, where high precision is paramount. The paper presents a comprehensive overview of the theoretical concepts and potential advancements offered by this approach, laying the groundwork for future experimental investigations.
Precision measurement plays a vital role in metrology. To achieve the ultimate precision predicted by quantum theory, one can leverage quantum entanglement—correlations between particles of light or matter that cannot be explained in classical physics. The use of quantum entanglement in probing an object enhances measurement precision by a factor of √N beyond what is attainable with classical resources, where precision is typically limited by Poisson noise. Here, N represents the number of entangled particles. To date, most research efforts have focused on understanding and characterizing non-classical correlations between two particles. For instance, in 2022, optical clocks were synchronized using quantum entanglement, achieving frequency uncertainties of √2 lower than what is possible with non-entangled clocks. However, despite rapid advancements in single-particle sensing technologies, the generation and characterization of quantum correlation involving three or more particles remain an ongoing challenge. The absence of rigorous measurement standards for multi-particle entanglement, coupled with the lack of photon-number-resolving (PNR) detection capabilities, can lead to faulty measurements and reduced metrological accuracy and precision. It is therefore essential to establish robust methodologies and standards for the creation and validation of multi-particle entanglement to enable quantum-limited precision measurements. These developments will provide significant impacts in various fields, including optical astronomy, frequency standards, microscopy, and secure communication. The integration of entanglement-assisted sensors with PNR detection will enhance imaging resolution in applications such as astronomy and biological sample analysis. Additionally, standardized metrological frameworks for quantum entanglement and hardware evaluation will enhance the security level of quantum communication by mitigating vulnerabilities associated with inconsistencies arising from the use of dissimilar characterization methodologies. These fundamental research efforts will have far-reaching implications, not only improving the quality of quantum measurements but also guiding national metrology institutes in developing standardized quantum measurement protocols.
Squeezed light, a prominent non-classical state of light, exhibits reduced quantum noise in one quadrature component below the standard quantum limit (SQL). The property enables quantum-enhanced precision measurements, surpassing the SQL in quantum sensing applications. This review comprehensively introduces the fundamental concepts, classifications, and experimental generation techniques of squeezed light. It further explores its pivotal role and recent advances in diverse quantum sensing domains, including interferometry, gravitational wave detection, magnetometry, force sensing, biomedical sensing, and quantum radar. The review covers theoretical foundations of squeezed states (including quadrature operators and classification schemes, experimental generation techniques in atomic ensembles, nonlinear crystals, and fibers), fundamentals of quantum sensing with squeezed light (from quantum noise theory to quantum-enhanced metrology), and quantum-enhanced sensing applications across the aforementioned domains. Finally, future challenges and opportunities in the field are discussed.