Quantum-enhanced optical phase tracking is a quantum optical technique for tracking and measuring optical phases with high accuracy. It has important applications in laser interferometry, spectral analysis, and optical measurements. In this study, we propose a quantum-enhanced optical phase tracking protocol based on squeezed state optical fields. By using a continuous solid-state laser source with a central wavelength of 1064 nm, combing second harmonic generation, optical parametric oscillator, and PDH (Pound-Drever-Hall) locking technology, we prepare an initial squeezed state with a squeezing level of (8.0±0.2) dB. Through signal modulation technique and demodulation technique, we control the phase of the squeezed state optical field, thereby realizing the quantum-enhanced tracking of optical phases within the range of 0－2π. Compared with classical protocols, this protocol can suppress the noise fluctuations of phase tracking to at least 6.27 dB below the shot noise limit, improving the phase tracking accuracy by more than 76.4%. Because of the high requirements for phase measurement accuracy in applications such as angle estimation, phased array radar, and phased array sonar, this protocol is expected to improve the phase estimation accuracy beyond the shot noise limit. It provides compressed light sources for relevant fields, laying a theoretical and experimental foundation for higher-precision spatial positioning and quantum ranging techniques. The probe is made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is determined by a gene and encoded in the genetic code. This can happen either before the protein is used in the cell, or as part of control mechanism.
Quantum-enhanced optical phase tracking is a quantum optical technique for tracking and measuring optical phases with high accuracy. It has important applications in laser interferometry, spectral analysis, and optical measurements. In this study, we propose a quantum-enhanced optical phase tracking protocol based on squeezed state optical fields. By using a continuous solid-state laser source with a central wavelength of 1064 nm, combing second harmonic generation, optical parametric oscillator, and PDH (Pound-Drever-Hall) locking technology, we prepare an initial squeezed state with a squeezing level of (8.0±0.2) dB. Through signal modulation technique and demodulation technique, we control the phase of the squeezed state optical field, thereby realizing the quantum-enhanced tracking of optical phases within the range of 0－2π. Compared with classical protocols, this protocol can suppress the noise fluctuations of phase tracking to at least 6.27 dB below the shot noise limit, improving the phase tracking accuracy by more than 76.4%. Because of the high requirements for phase measurement accuracy in applications such as angle estimation, phased array radar, and phased array sonar, this protocol is expected to improve the phase estimation accuracy beyond the shot noise limit. It provides compressed light sources for relevant fields, laying a theoretical and experimental foundation for higher-precision spatial positioning and quantum ranging techniques. The probe is made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is determined by a gene and encoded in the genetic code. This can happen either before the protein is used in the cell, or as part of control mechanism.
This thesis reports the development of a quantum enhanced microparticle tracking technique, which applied to measurements within living cells, allowed the first demonstrations of both biological measurements beyond the quantum noise limit and quantum enhanced spatial resolution within biology. The sensitivity of any optical measurement is limited by noise which follows from quantization of the electromagnetic field. This thesis theoretically characterizes the resulting quantum limit on particle tracking precision; both in the limit of perfect measurements and for the measurements used in real experiments, and theoretically establishes an experimental strategy which could allow the quantum limit to be surpassed via the application of non-classical light. Further, a computational tool is developed which allows rapid characterization of particle tracking experiments, thus providing researchers the benefit of rigorous theoretical predictions without requiring detailed calculations. Following this, classical technologies are developed which can improve microparticle tracking sensitivity and which are enabling steps toward integration of non-classical light. An interferometric strategy is described whereby signal-to-noise is improved by removing unwanted light from the detector. An optical lock-in technique is developed which eliminates low-frequency noise, thus allowing quantum noise limited performance at low frequencies. This is a crucial requirement for quantum enhanced measurements, and can also improve precision in classical experiments. Dark-field illumination is also explored as a method to remove unwanted background light, and the optimal illumination angle is calculated for our intended experiments. These advances are then applied in the development of the first quantum enhanced particle tracking apparatus. Squeezed states of light are used to improve particle tracking precision by 2.7 dB, demonstrating quantum enhanced microscopy for the first time. This was applied to perform the first measurements of living systems with quantum enhanced precision. Naturally occurring lipid particles were tracked within the cytoplasm of Saccharomyces cerevisiae yeast cells, with squeezed light enhancing precision by 2.4 dB. The thermal motion of these particles could then be analyzed to infer the viscosity and elasticity of the local environment, with squeezed light allowing 64% faster observations, thus improving the sensitivity to dynamic biological changes. This experiment was then extended to spatially resolved quantum imaging, with lipid particles used as scanning probes in a technique called photonic force microscopy. The particles sample variations in the local environment with resolution limited by measurement precision rather than the diffraction limit. The use of squeezed light was found to enhance spatial resolution by 14% at an absolute resolution level of 10 nm, comparable to leading classical experiments. This was the first demonstration of both sub-diffraction limited resolution and quantum enhanced resolution in biology, and places practical applications of quantum imaging within reach. Finally, the future challenges and prospects of quantum enhanced particle tracking are outlined.n
This research focuses on advanced noise suppression technologies for high-precision measurement systems, particularly addressing the limitations of classical noise reducing approaches. The noise level of laser sources is a crucial factor that directly affects the measurement sensitivity in applications such as gravitational wave detection and biomedical imaging. Classical feedback control technologies are effective but often encounter a bottleneck resulting from the classical noise suppression limits. To cope with these challenges, a novel method integrating quantum squeezed light with classical feedback control systems to reduce intensity noise is proposed in this work. By employing an amplitude-squeezed light field, a quantum-enhanced feedback control model is developed, thereby theoretically examining the influence of both the feedback loop gain and the degree of squeezing on the noise suppression performance. The results show that the injection of squeezed light significantly reduces the intensity noise, approaching the shot noise limit (SNL), thereby improving the system sensitivity beyond the classical noise reduction boundaries. Specifically, –10 dB squeezed state injection into the feedback system yields an additional noise suppression of approximately 8.97 dB, exceeding what is achievable using classical feedback alone. This demonstrates that the potential of the proposed method can enhance measurement precision close to the quantum noise limits without increasing the laser power. The analysis highlights the asymmetric noise suppression effects between the inner feedback loop and outer feedback loop. Although the outer loop benefits significantly from the squeezed light injection and achieves noise levels that are unattainable by classical feedback methods, the inner loop shows relatively minor improvements. This asymmetry is attributed to the inherent characteristics of quantum squeezing and the limitations of the feedback loop design. Further investigation into the individual noise components reveals that the primary contributors to the intensity noise include input noise, photodetector noise, and beam splitter-induced vacuum fluctuations. The injection of squeezed light effectively mitigates these vacuum fluctuations, which are typically a major noise source in high-precision laser systems. Theoretical research results show that the use of squeezed light in feedback control systems can effectively enhance noise suppression, equivalent to a nine fold increase in detected optical power, without the physical drawbacks of increasing laser power such as thermal noise. In conclusion, this study provides a theoretical validation of combining quantum squeezed states with classical feedback control to exceed classical noise suppression limits. The integration of a –10 dB squeezed state demonstrates a significant noise reduction, showing that this hybrid approach could revolutionize noise management in precision measurement applications. The results pave the way for further exploring quantum-enhanced control technologies in fields such as gravitational wave detection, quantum communication, and advanced optical sensing, providing a pathway for improving sensitivity and noise suppression without increasing additional power requirements.
Quantum sensing, along with quantum communications and quantum computing, is commonly considered as the most important application of quantum optics. Among the quantum-sensing experiments, schemes based on squeezed states of light are popular choices due to their natural quadrature components. Since the first experimental demonstration of quantum-squeezing-enhanced phase measurement beyond the shot-noise limit in 1987, quantum-squeezing techniques toward practical sensing and tracking have been extensively investigated. In this paper, we briefly review the recent developments of quantum squeezing and its applications in several advanced systems for measurements of position, rotation, dynamic motion, magnetic fields, and gravitational waves. We also introduce the recent experimental efforts to combine the quantum-squeezing lights into fiber sensing systems.
Stable low-frequency squeezed vacuum states at a wavelength of 1550 nm were generated. By controlling the squeezing angle of the squeezed vacuum states, two types of low-frequency quadrature-phase squeezed vacuum states and quadrature-amplitude squeezed vacuum states were obtained using one setup respectively. A quantum-enhanced fiber Mach–Zehnder interferometer (FMZI) was demonstrated for low-frequency phase measurement using the generated quadrature-phase squeezed vacuum states that were injected. When phase modulation was measured with the quantum-enhanced FMZI, there were above 3 dB quantum improvements beyond the shot-noise limit (SNL) from 40 kHz to 200 kHz, and 2.3 dB quantum improvement beyond the SNL at 20 kHz was obtained. The generated quadrature-amplitude squeezed vacuum state was applied to perform low-frequency amplitude modulation measurement for sensitivity beyond the SNL based on optical fiber construction. There were about 2 dB quantum improvements beyond the SNL from 60 kHz to 200 kHz. The current scheme proves that quantum-enhanced fiber-based sensors are feasible and have potential applications in high-precision measurements based on fiber, particularly in the low-frequency range.
Quantum techniques, developed in recent decades, provide new approaches to achieving high-precision measurements beyond the classical bounds. In this paper, we theoretically demonstrate a metrology method for improving the sensitivity of the interferometric optical gyroscope, robust against the loss, by using coherent-light stimulated two-mode squeezed beams as the light source. The detection protocol is based on a simple intensity measurement, and the quantum noise is far below the shot-noise limit. The enhancement factors for different coherent light fields are analyzed in detail. Additionally, the influence of loss during the propagation in the optical path is studied, and the conditions for achieving sub-shot-noise measurement sensitivity are obtained. We also find that the phase sensitivity of the proposed gyroscope scheme becomes closer to the quantum Cramér-Rao bound with increasing of the photon number of the coherent beams.
Quantum metrology enables estimation of optical phase shifts with precision beyond the shot-noise limit. One way to exceed this limit is to use squeezed states, where the quantum noise of one observable is reduced at the expense of increased quantum noise for its complementary partner. Because shot-noise limits the phase sensitivity of all classical states, reduced noise in the average value for the observable being measured allows for improved phase sensitivity. However, additional phase sensitivity can be achieved using phase estimation strategies that account for the full distribution of measurement outcomes. Here we experimentally investigate a model of optical spin-squeezing, which uses post-selection and photon subtraction from the state generated using a parametric downconversion photon source, and we investigate the phase sensitivity of this model. The Fisher information for all photon-number outcomes shows it is possible to obtain a quantum advantage of 1.58 compared to the shot-noise value for five-photon events, even though due to experimental imperfection, the average noise for the relevant spin-observable does not achieve sub-shot-noise precision. Our demonstration implies improved performance of spin squeezing for applications to quantum metrology.