The measurement of the frequency fluctuations of an optical field

Michael Z. Smirnov

Dong-Chel Shin, Edwin Ng, Myoung-Gyun Suh +1 more

Frequency combs enable precision measurements across timekeeping, spectroscopy, ranging and astronomy, and are now extending to integrated and field-deployable platforms. Realizing their full performance demands a comprehensive account of the quantum noise that arises when broadband optical fields are converted into finite-bandwidth electrical signals. Here we present a rigorous first-principles quantum-mechanical framework for optical frequency-comb metrology based on continuous-mode field quantization and a comb-line-resolved description of quantum fluctuations. The theory describes how quantum fluctuations of the comb field are transduced into electrical measurement noise. Formulated at the level of the comb field, the framework unifies the standard quantum limits of optical frequency division (OFD) and dual-comb spectroscopy (DCS) within a single treatment, and provides a general recipe for other comb-based measurements. On this footing, we identify practical, resource-efficient routes to quantum enhancement through engineered comb states, laying a foundation for the design of next-generation frequency combs operating at and beyond standard quantum limits.

Matthieu Ansquer, Valérian Thiel, Syamsundar De +4 more

Controlling the noise properties of optical frequency combs (OFC) is of great importance as most OFC-based precision measurements are limited by their intrinsic stability. It has been found that OFC noise manifests itself as fluctuations of only a few global parameters, which indicates strong correlations between the fluctuations of individual frequency lines. However, the physical processes underneath such correlations are still not completely understood. We introduce a novel measurement scheme that allows us to measure simultaneously and in real time the whole Fourier spectrum of phase and amplitude fluctuations of the OFC field as well as its amplitude-phase correlations in many frequency bands spanning the laser spectrum. This enables us to determine the full quadrature covariance matrices in the frequency band mode basis, and this for various Fourier frequencies, to find their principal modes in time and frequency domain, and to associate them with global physical parameters.

Harry J. Kimble

Evgenii B. Aleksandrov, A. M. Bonch-Bruevich, N. N. Kostin +1 more

Ning Zhang, Qiang Guo, Wen Ye +2 more

Nitrogen-vacancy (NV) centers in diamonds play a large role in advanced quantum sensing with solid-state spins for potential miniaturized and portable application scenarios. With the temperature sensitivity of NV centers, the temperature fluctuations caused by the unknown environment and the system itself will mix with the magnetic field measurement. In this research, the temperature-sensitive characteristics of different diamonds, alongside the temperature noise generated by a measurement system, were tested and analyzed with a homemade NV magnetometer in a fiber-optic scheme. In this work, a multi-frequency synchronous manipulation method for resonating with the NV centers in all axial directions was proposed to compensate for the temperature fluctuations in a fibered NV magnetic field sensing scheme. The symmetrical features of the resonance lines of the NV centers, the common-mode fluctuations including temperature fluctuations, underwent effective compensation and elimination. The fluorescence change was reduced to 1.0% by multi-frequency synchronous manipulation from 5.5% of the single-frequency manipulation within a ±2 °C temperature range. Additionally, the multi-frequency synchronous manipulation improved the fluorescence contrast and the magnetic field measurement SNR through an omnidirectional manipulation scheme. It was very important to compensate for the temperature fluctuations, caused by both internal and external factors, to make use of the NV magnetometer in fiber-optic schemes' practicality. This work will promote the rapid development and widespread applications of quantum sensing based on various systems and principles.