Fundamental light-field measurement schemes

Modern precision measurements, such as interferometry for detecting gravitational waves, rely on the estimation of optical phases encoded in light fields. Here, we propose to exploit the collectively enhanced output field of a driven-dissipative many-body quantum system as a light source in order to improve the precision of estimating optical phases. Pronounced temporal correlations of such output fields benefit the sensitivity of measurement protocols, which we show theoretically by employing a boundary time crystal as a light source. The fundamental bound on the precision of such estimation shows scaling with the number of constituents $N$ of the many-body system as $N^4$ while scaling linearly with the measurement time $T$ . We discuss this scaling both from a perspective of the resources employed to build the light source and of the resources produced by the light source. We show that a measurement scheme, in which the phase shifted light field is guided into an auxiliary replica system, which serves as a detector that is sensitive to non-trivial temporal correlations of light, can saturate the fundamental bound on precision at an optimal operating point.Modern precision measurements, such as interferometry for detecting gravitational waves, rely on the estimation of optical phases encoded in light fields. Here, we propose to exploit the collectively enhanced output field of a driven-dissipative many-body quantum system as a light source in order to improve the precision of estimating optical phases. Pronounced temporal correlations of such output fields benefit the sensitivity of measurement protocols, which we show theoretically by employing a boundary time crystal as a light source. The fundamental bound on the precision of such estimation shows scaling with the number of constituents $N$ of the many-body system as $N^4$ while scaling linearly with the measurement time $T$. We discuss this scaling both from a perspective of the resources employed to build the light source and of the resources produced by the light source. We show that a measurement scheme, in which the phase shifted light field is guided into an auxiliary replica system, which serves as a detector that is sensitive to non-trivial temporal correlations of light, can saturate the fundamental bound on precision at an optimal operating point.

quant-pharXiv:2511.23416Dec 1, 20250 citations

Advanced measurements for quantum photonics and quantum technologies

David Phillips

Measurements on states of light underpins the entire fields of classical and quantum optics. Without measurement we are unable to gain any information about the light we are studying or about the processes it has undergone. The property of the density matrix of light prior to measurement that we want to measure also relies heavily on the measurement technique we employ. We can use a single-photon detector to measure the particle nature of light--the photon--the discrete quanta of the electromagnetic field. We can conversely measure the wave nature of the light field by making phase-sensitive measurements. In this thesis, we shall explore some advanced implementations and applications of these measurement schemes. First, we shall focus on a specific type of single-photon detector: the Superconducting-Nanowire Single-Photon Detector. We will first consider the integration of these detectors on optical waveguides, and discuss their optical characterisation. Then we will consider a practical application of these detectors by investigating a method to perform broadband spectroscopy with a single detector. We shall then progress to phase-sensitive measurements, and consider the intermediate regime between measuring the wave-like and particle-like nature of light. First we will perform a fundamental investigation of the transition between both measurement regimes. We will see how varying the phase reference itself allows us to tune between both regimes. Following this we will discuss an application of this intermediate regime, by considering an experimental setup to perform state tomography with a weak phase reference. The final consideration of this thesis will be a theoretical benchmarking scheme for a practical application of quantum optics. The manipulation of certain quantum states of light followed by a photon-number measurement can have practical applications in a variety of fields, and therefore validating the results is of extreme importance. On this final topic, we will discuss an experimentally friendly technique to benchmark the output of such measurements by considering smaller subsystems, and the practical requirements of this technique.Measurements on states of light underpins the entire fields of classical and quantum optics. Without measurement we are unable to gain any information about the light we are studying or about the processes it has undergone. The property of the density matrix of light prior to measurement that we want to measure also relies heavily on the measurement technique we employ. We can use a single-photon detector to measure the particle nature of light--the photon--the discrete quanta of the electromagnetic field. We can conversely measure the wave nature of the light field by making phase-sensitive measurements. In this thesis, we shall explore some advanced implementations and applications of these measurement schemes. First, we shall focus on a specific type of single-photon detector: the Superconducting-Nanowire Single-Photon Detector. We will first consider the integration of these detectors on optical waveguides, and discuss their optical characterisation. Then we will consider a practical application of these detectors by investigating a method to perform broadband spectroscopy with a single detector. We shall then progress to phase-sensitive measurements, and consider the intermediate regime between measuring the wave-like and particle-like nature of light. First we will perform a fundamental investigation of the transition between both measurement regimes. We will see how varying the phase reference itself allows us to tune between both regimes. Following this we will discuss an application of this intermediate regime, by considering an experimental setup to perform state tomography with a weak phase reference. The final consideration of this thesis will be a theoretical benchmarking scheme for a practical application of quantum optics. The manipulation of certain quantum states of light followed by a photon-number measurement can have practical applications in a variety of fields, and therefore validating the results is of extreme importance. On this final topic, we will discuss an experimentally friendly technique to benchmark the output of such measurements by considering smaller subsystems, and the practical requirements of this technique.

Jan 1, 20200 citations

Coherence of Light Fields

Kedar Khare, Mansi Butola, Sunaina Rajora

Springer eBooksJan 1, 20230 citations

Full-dimensional complex coherence properties tomography for multi-cipher information security

Yonglei Liu, Siting Dai, Yimeng Zhu +4 more

Optical coherence is a fundamental property of light, playing a key role in understanding interference, propagation, and light-matter interactions for both classical and quantum light. Measuring the coherence properties of an optical field is crucial for a wide range of applications. However, despite many proposed measurement schemes, significant challenges still remain. In this work, we present a protocol to measure the full-dimensional coherence properties of a partially coherent beam. The method is based on tomographing the complex coherent modes of the partially coherent field within its coherence time. Once the complex coherent modes are reconstructed, all coherence properties including field correlation and its higher-order correlations (e.g., intensity correlation) can be recovered for beams that are either spatially uniformly or non-uniformly correlated. We perform a proof-of-principle experiment to measure the complex field correlation and intensity correlation of a structured partially coherent beam synthesized by random modes. Additionally, we discuss the application of full-dimensional complex coherence function tomography in coherence-based multi-cipher information security. The robustness of our system in complex environments is also evaluated.Optical coherence is a fundamental property of light, playing a key role in understanding interference, propagation, and light-matter interactions for both classical and quantum light. Measuring the coherence properties of an optical field is crucial for a wide range of applications. However, despite many proposed measurement schemes, significant challenges still remain. In this work, we present a protocol to measure the full-dimensional coherence properties of a partially coherent beam. The method is based on tomographing the complex coherent modes of the partially coherent field within its coherence time. Once the complex coherent modes are reconstructed, all coherence properties including field correlation and its higher-order correlations (e.g., intensity correlation) can be recovered for beams that are either spatially uniformly or non-uniformly correlated. We perform a proof-of-principle experiment to measure the complex field correlation and intensity correlation of a structured partially coherent beam synthesized by random modes. Additionally, we discuss the application of full-dimensional complex coherence function tomography in coherence-based multi-cipher information security. The robustness of our system in complex environments is also evaluated.

Opto-Electronic AdvancesJan 1, 202518 citations

Measuring the quantum state of light

Ulf Leonhardt, Henryk Paul

Progress in Quantum ElectronicsJan 1, 1995189 citations

N

of the many-body system as

N^4

while scaling linearly with the measurement time

T

. We discuss this scaling both from a perspective of the resources employed to build the light source and of the resources produced by the light source. We show that a measurement scheme, in which the phase shifted light field is guided into an auxiliary replica system, which serves as a detector that is sensitive to non-trivial temporal correlations of light, can saturate the fundamental bound on precision at an optimal operating point.