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The Journal of Chemical Physics

Beyond photon shot noise: Chemical limits in spectrophotometric precision

Georg Engelhardt, Dahai He, JunYan Luo

Published May 6, 2026• 0 citations
Publisher

Abstract

In this work, we investigate precision limitations in spectrophotometry (i.e., spectroscopic concentration measurements) imposed by chemical processes of molecules. Using the recently developed photon-resolved Floquet theory, which generalizes Maxwell-Bloch theory for higher-order measurement statistics, we analyze a molecular model system subject to chemical reactions whose electronic and optical properties depend on the chemical state. Analysis of sensitivity bounds reveals: (i) Phase measurements are more sensitive than intensity measurements; (ii) sensitivity exhibits three regimes: photon-shot-noise limited, chemically limited, and intermediate; and (iii) sensitivity shows a turnover as a function of reaction rate due to the interplay between coherent electronic dynamics and incoherent chemical dynamics. Our findings demonstrate that chemical properties must be considered to estimate ultimate precision limits in optical spectrophotometry.

DOI
10.1063/5.0324892

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The article is written in a popular science convention.It concerns issues related to generally understood issues that are involved in explaining the principles of the impact of the measurement beam in spectrophotometric research.To explain this, we need to answer basic questions about what a photon is?What is wave-particle dualism?What do chemical bonds look like?What conditions must be met for a photon to be adsorbed by a chemical moiety?There are many inaccuracies in the current theories that do not explain the observed phenomena.The phenomenological models of the photon and chemical bonds that I have created are intended to explain photoelectric and optical phenomena that are not explained by either the wave or particle nature of photons.There is also no clear model of chemical bonds that would explain the phenomena observed in spectrophotometry.Phenomenological considerations are accompanied by several physical considerations and calculations in order to illustrate certain phenomena and proportions prevailing on the atomic scale.The above considerations are of a debatable nature and are an attempt to break away from stereotypical concepts operating in the world of science.Spectrophotometry is an analytical method that combines theories about photons, the structure of matter and phenomena that concern their mutual interactions.The phenomena visible in it can be interpreted more easily using my phenomenological image of matter.

Polis Journal of Materials and Environmental Engineering•Jan 1, 2024•0 citations
In this work, we investigate precision limitations in spectrophotometry (i.e., spectroscopic concentration measurements) imposed by chemical processes of molecules. Using the recently developed photon-resolved Floquet theory, which generalizes Maxwell-Bloch theory for higher-order measurement statistics, we analyze a molecular model system subject to chemical reactions whose electronic and optical properties depend on the chemical state. Analysis of sensitivity bounds reveals: (i) Phase measurements are more sensitive than intensity measurements; (ii) sensitivity exhibits three regimes: photon-shot-noise limited, chemically limited, and intermediate; and (iii) sensitivity shows a turnover as a function of reaction rate due to the interplay between coherent electronic dynamics and incoherent chemical dynamics. Our findings demonstrate that chemical properties must be considered to estimate ultimate precision limits in optical spectrophotometry.
In this work, we investigate precision limitations in spectrophotometry (i.e., spectroscopic concentration measurements) imposed by chemical processes of molecules. Using the recently developed Photon-resolved Floquet theory, which generalizes Maxwell-Bloch theory for higher-order measurement statistics, we analyze a molecular model system subject to chemical reactions whose electronic and optical properties depend on the chemical state. Analysis of sensitivity bounds reveals: (i) Phase measurements are more sensitive than intensity measurements; (ii) Sensitivity exhibits three regimes: photon-shot-noise limited, chemically limited, and intermediate; (iii) Sensitivity shows a turnover as a function of reaction rate due to the interplay between coherent electronic dynamics and incoherent chemical dynamics. Our findings demonstrate that chemical properties must be considered to estimate ultimate precision limits in optical spectrophotometry.
Quantum entanglement, a hallmark of quantum mechanics, offers unprecedented opportunities to revolutionize spectroscopic techniques. This paper explores the theoretical underpinnings and experimental prospects of quantum entanglement-enhanced spectroscopy for the precise probing of coherent dynamics in complex chemical systems. Traditional spectroscopic methods often face limitations in resolution, sensitivity, and the ability to distinguish subtle quantum phenomena due to their reliance on classical light sources. By harnessing entangled photons, it is possible to overcome these limitations, enabling sub-shot-noise measurements, enhanced spectral resolution beyond the diffraction limit, and access to non-classical correlations within molecular systems. We delve into how entangled light can be generated and engineered to interact with molecular ensembles, facilitating the study of processes such as exciton transport, charge transfer, and vibrational energy redistribution with extraordinary fidelity. The methodology section outlines conceptual experimental setups, including entangled two-photon absorption spectroscopy and quantum Ramsey interferometry, discussing the benefits of these approaches over their classical counterparts. We present hypothetical results demonstrating how entanglement can resolve overlapping spectral features, extend coherence lifetimes, and provide unique insights into the quantum pathways governing chemical reactions. The discussion addresses the challenges associated with maintaining entanglement in noisy chemical environments and outlines strategies for mitigating decoherence. Ultimately, entanglement-enhanced spectroscopy represents a transformative paradigm for chemical physics, promising a deeper understanding of fundamental quantum processes that dictate reactivity and function in biological and material sciences.
The ultimate sensitivity of optical measurements is a key element of many recent works. Classically, it is mainly limited by the shot noise limit. However, a measurement setup that incorporates quantum mechanical principles can surpass the shot noise limit and reach the Heisenberg limit. Nevertheless, many of those experiments fail to break even the classical shot-noise limit. Following a recent proposal, we present here the results of optical phase measurements with a photon-number resolving detector using coherent states of up to 4200 photons on average. An additional scheme that can be implemented using standard single-photon detectors is also presented, and the results of the two schemes are compared. These measurements present deterministic single-shot sub-wavelength super-resolution up to 288 better than the optical wavelength. The results follow the classically limited sensitivity, up to 86 times better than the wavelength.
Optical techniques are widely used in many areas of science and technology to make accurate measurements and diagnostics, from microscopy, spectroscopy, chemical analysis, to gravitational wave detection and ranging. There are many reasons for this: light allows us to extract information in a remote and non-destructive way, it carries information in a massively parallel way, and perhaps more importantly, optical measurements can reach very high precision and sensitivity levels. It is therefore important to know what is the ultimate limit of sensitivity that can be possibly achieved in the estimation of a physical parameter p that is encoded in a light beam of fixed mean photon number N. This limit is imposed by the unavoidable quantum fluctuations of light and depends on the quantum state of light that conveys the information about p. When the light is in a coherent state, this limit is called ‘standard quantum limit’ and scales as 1/N1/2.
Absorption spectroscopy is one of the most widely used spectroscopic methods. The signal-to-noise ratio in conventional absorption spectroscopy is ultimately limited by the shot noise, which arises from the statistical property of the light used for the measurement. Here we show that the noise in absorption spectra can be suppressed below the shot-noise limit when entangled photon pairs are used for the light source. By combining broadband entangled photon pairs and multichannel detection, we realize the acquisition of sub-shot-noise absorption spectra in the entire visible wavelength. Furthermore, we demonstrate the strength of sub-shot-noise absorption spectroscopy for the identification and quantification of chemical species, which are two primary aims of absorption spectroscopy. For highly diluted binary mixture solutions, sub-shot-noise absorption spectroscopy enables us to determine the concentration of each chemical species with precision beyond the limit of conventional absorption spectroscopy. That is, sub-shot-noise absorption spectroscopy achieves superresolution in concentration measurements.
The article is written in a popular science convention.It concerns issues related to generally understood issues that are involved in explaining the principles of the impact of the measurement beam in spectrophotometric research.To explain this, we need to answer basic questions about what a photon is?What is wave-particle dualism?What do chemical bonds look like?What conditions must be met for a photon to be adsorbed by a chemical moiety?There are many inaccuracies in the current theories that do not explain the observed phenomena.The phenomenological models of the photon and chemical bonds that I have created are intended to explain photoelectric and optical phenomena that are not explained by either the wave or particle nature of photons.There is also no clear model of chemical bonds that would explain the phenomena observed in spectrophotometry.Phenomenological considerations are accompanied by several physical considerations and calculations in order to illustrate certain phenomena and proportions prevailing on the atomic scale.The above considerations are of a debatable nature and are an attempt to break away from stereotypical concepts operating in the world of science.Spectrophotometry is an analytical method that combines theories about photons, the structure of matter and phenomena that concern their mutual interactions.The phenomena visible in it can be interpreted more easily using my phenomenological image of matter.