Measuring the polarization states of light and their variations, a process known as polarimetry, is essential to modern metrology, especially within the field of optical rotation. However, enhancing the precision of such measurements by improving the detectors is challenging, primarily due to the limitation in photoelectric response. By contrast, the scheme of quantum polarimetry has shown that exploiting correlated particles as the probe can provide an enhancement in the precision. Inspired by the scheme, by introducing correlations among classical light beams, we demonstrate that the precision of polarimetry focused on optical rotation can be enhanced. This conclusion is supported by both our theoretical analysis and experimental results. And we call it correlated optical polarimetry. Because the correlated beams we consider are spatially separable, a distributed optical rotation polarimetry scheme is given, which can be applied for the detection of spatially distributed but homogeneous objects. Our results show that the maximal improvements of the precision scales are proportional to the square root of the probe number, and we verify the results by experiments when the probe number is 2, 4, and 6. The scaling of precision improvements mathematically resembles the transition from shot-noise scaling to Heisenberg scaling in quantum metrology, but works for a classical light detection system. Hence, it helps enhance the traditional light-based polarization measure and other relevant practical applications.
Measuring the polarization states of light and their variations, a process known as polarimetry, is essential to modern metrology, especially within the field of optical rotation. However, enhancing the precision of such measurements by improving the detectors is challenging, primarily due to the limitation in photoelectric response. By contrast, the scheme of quantum polarimetry has shown that exploiting correlated particles as the probe can provide an enhancement in the precision. Inspired by the scheme, by introducing correlations among classical light beams, we demonstrate that the precision of polarimetry focused on optical rotation can be enhanced. This conclusion is supported by both our theoretical analysis and experimental results. And we call it correlated optical polarimetry. Because the correlated beams we consider are spatially separable, a distributed optical rotation polarimetry scheme is given, which can be applied for the detection of spatially distributed but homogeneous objects. Our results show that the maximal improvements of the precision scales are proportional to the square root of the probe number, and we verify the results by experiments when the probe number is 2, 4, and 6. The scaling of precision improvements mathematically resembles the transition from shot-noise scaling to Heisenberg scaling in quantum metrology, but works for a classical light detection system. Hence, it helps enhance the traditional light-based polarization measure and other relevant practical applications.
Abstract Classical polarimetry is a well-established discipline with diverse applications across different branches of science. The burgeoning interest in leveraging quantum resources to achieve highly sensitive measurements has spurred researchers to elucidate the behavior of polarized light within a quantum mechanical framework, thereby fostering the development of a quantum theory of polarimetry. In this work, drawing inspiration from polarimetric investigations in biological tissues, we investigate the precision limits of polarization rotation angle estimation about a known rotation axis, in a quantum polarimetric process, comprising three distinct quantum channels. The rotation angle to be estimated is induced by the retarder channel on the Stokes vector of the probe state. The diattenuator and depolarizer channels, acting on the probe state, can be thought of as effective noise processes. We explore the precision constraints inherent in quantum polarimetry by evaluating the quantum Fisher information for probe states of significance in quantum metrology, namely NOON, Kings of Quantumness, and Coherent states. The effects of the noise channels as well as their ordering is analyzed on the estimation error of the rotation angle to characterize practical and optimal quantum probe states for quantum polarimetry. Furthermore, we propose an experimental framework tailored for NOON state quantum polarimetry, aiming to bridge theoretical insights with empirical validation.
It takes some convincing to realize that light has a polarization degree of freedom, as our eyes are usually ignorant of light's polarization. Since overcoming this hurdle of intuition, polarization has become a fantastic resource that can be easily manipulated both physically and mathematically, opening the door to a wide variety of applications. We have only recently begun to appreciate how many more doors are opened by the quantum mechanical degrees of freedom inherent to optical polarization. One use of optical polarization is for polarimetry: measuring the changes in light's polarization after it interacts with a material is an excellent procedure for nondestructively probing the characteristics and composition of the intervening material. More sensitive measurements require brighter probe light; however, sufficiently intense light will begin to destroy the sample being probed. In this thesis, we seek to provide more sensitive polarimetry without resorting to bright beams of light. Tailoring the quantum properties of various states of light has been shown to increase their usefulness for other estimation protocols and we show how to extend this paradigm to quantum enhancements in polarimetry. We begin by finding the quantum states underlying classical polarization. Each particular set of classical polarization properties corresponds to a large variety of quantum states. Next, we establish quantum descriptions of classical polarization transformations corresponding to arbitrary Jones and Mueller matrices, including quantum mechanical insights into the distinction between processes that can and cannot be described by Jones matrices. We propose candidates for the most likely quantum states underlying classical decompositions into polarized and unpolarized fractions, carefully inspecting how these quantum states behave under polarization transformations. This language allows us to inspect quantum-enhanced sensing in the multiparameter context of polarimetry. We show the dramatic possibilities for quantum enhancements in any metrological scenario that is mathematically equivalent to a rotation, of which polarization rotations are a primary example; in contrast, we also show most attenuating and depolarizing polarization transformations to forbid such dramatic enhancements. Finally, we discuss polarization and its generalizations in the context of generating quantum entanglement via linear optics. These applications serve as mere examples of the usefulness promised by light’s quantum polarization degrees of freedom.
Quantum non-demolition measurement with an off-resonance polarized probe is a widely utilized technique for atomic sensors. Typically, QND instruments read out spin states through optical polarimetry using a linearly off-resonance probe in atomic media. This optical read-out process offers high accuracy, with potential applications in biomagnetism, inertial navigation and new physics exploration beyond the standard model. It was observed that previously unexplored spin-alignment polarization induced by the far-detuned off-resonance linear probe in an ultrasensitive optical polarimetry. The evolution of probe-generated multipole moments exacerbates probe noise due to strong magnetic couplings. A method was demonstrated to decouple spin-alignment from magnetic fields by manipulating the multipole moments in zero fields. A suppression of the probe noise by 8.2 dB at 1 Hz and 10.4 dB at 10 Hz with the proposed method, reaching the standard quantum limit, was achieved. The realized shot-noise-limited optical polarimetry shows significant potential for advancing the performance of atomic sensors, particularly in applications requiring ultra-high sensitivity, such as precision measurements and quantum metrology. These findings provide a pathway toward enhanced sensor precision in diverse scientific and technological applications.
The development of new techniques to improve measurements is crucial for all sciences. By employing quantum systems as sensors to probe some physical property of interest allows the application of quantum resources, such as coherent superpositions and quantum correlations, to increase measurement precision. Here we experimentally investigate a scheme for quantum target detection based on linear optical measurement devices, when the object is immersed in unpolarized background light. By comparing the quantum (polarization-entangled photon pairs) and the classical (separable polarization states) strategies, we found that the quantum strategy provides us an improvement over the classical one in our experiment when the signal-to-noise ratio is greater than 1/40, or about 16 dB of noise. This is in constrast to quantum target detection considering nonlinear optical detection schemes, which have shown resilience to extreme amounts of noise. A theoretical model is developed which shows that, in this linear-optics context, the quantum strategy suffers from the contribution of multiple background photons. This effect does not appear in our classical scheme. By improving the two-photon detection electronics, it should be possible to achieve a polarization-based quantum advantage for a signal-to-noise ratio that is close to 1/400 for current technology.
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.
Without light, there would be no sight. Light acts as a probe in various measurement techniques ranging from imaging to spectroscopy, from small scale cantilever displace- ment measurement in atomic force microscopy to large scale mirror motion in interfer- ometry, light detection and ranging (LIDAR) and many other fields. As the light probe intensity rises, it not only allows reducing the background noise effect, but it also aids precision to the measurement by reducing the photon noise (shot-noise) contribution. However, increasing intensity beyond certain threshold level is not always advantageous for ultra sensitive measurements. For example in the detection of gravitational waves, the current power circulating in the large scale interferometers can not be increased further without introducing other noise sources like thermal effects on the mirrors, un- wanted scattered photons, and back action due to radiation pressure. In the imaging of delicate photo sensitive sample, high power can causes cell damage or it may lead to disturb the regular process under investigation, viz. favouring certain biochemical reaction, which do not correspond to natural in vitro behaviour. At low intensity, pho- ton noise is an important concern and quantum states of light with correlated photon fluctuation can ideally represent a fruitful way to build specific measurement strategies to surpass the limitation of standard approach based on classical light sources, offering an avenue of solutions for ultra sensitive measurements. This thesis work focuses on two application of quantum enhanced measurement strate- gies. The first part of the thesis work has been dedicated to the realization of the first wide-field microscope with Sub Shot Noise (SSN) sensitivity. This is based on the ex- ploitation of quantum correlations in the Squeezed Vacuum state. In the second part, the investigations have made on the role of the quantum correlated beams in an unusual interferometric scheme, in which two identical optical interferometers are subject to the same phase fluctuation. The scheme, in the classical regime, has been already imple- mented in a large scale experiment devoted to the search of possible quantum gravity (QG) effects at Fermilab.