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We introduce a novel technique for the reconstruction of multimode optical fields, based on simultaneously exploiting both the generalized Glauber's $K^{th}$-order correlation function $g^{(K)}$ and a recently proposed anti-correlation function (dubbed $\theta^{(K)}$) which is resilient to Poissonian noise. We experimentally demonstrate that this method yields mode reconstructions with higher fidelity with respect to those obtained with reconstruction methods based only on $g^{(K)}$'s, even requiring less "a priori" information. The reliability and versatility of our technique make it suitable for a widespread use in real applications of optical quantum measurement, from quantum information to quantum metrology, especially when one needs to characterize ensembles of single-photon emitters in the presence of background noise (due, for example, to residual excitation laser, stray light, or unwanted fluorescence)., Comment: 11 pages, 3 figures

We report on the systematic characterization of the optical properties of diamond color centers based on Pb impurities. An ensemble photoluminescence analysis of their spectral emission was performed at different excitation wavelengths in the 405-520 nm range and at different temperatures in the 4-300 K range. The series of observed spectral features consist of different emission lines associated with Pb-related defects. Finally, a room-temperature investigation of single-photon emitters under 490.5 nm laser excitation is reported, revealing different spectral signatures with respect to those already reported under 514 nm excitation. This work represents a substantial progress with respect to previous studies on Pb-related color centers, both in the attribution of an articulated series of spectral features and in the understanding of the formation process of this type of defect, thus clarifying the potential of this system for high-impact applications in quantum technologies.

Understanding the human brain remains one of the most significant challenges of the 21st century. As theoretical studies continue to improve the description of the complex mechanisms that regulate biological processes, in parallel numerous experiments are conducted to enrich or verify these theoretical predictions and with the aim of extrapolating more accurate models. In the field of magnetometers for biological application, among the various sensors proposed for this purpose, NV centers have emerged as a promising solution due to their perfect biocompatibility and the possibility of being positioned in close proximity and even inside the cell, allowing a nanometric spatial resolution. There are still many difficulties that must be overcome in order to obtain both spatial resolution and sensitivity capable of revealing the very weak biological electromagnetic fields generated by neurons (or other cells). However, over the last few years, significant improvements have been achieved in this direction, thanks to the use of innovative techniques, which allow us to hope for an early application of these sensors for the measurement of fields such as the one generated by cardiac tissue, if not, in perspective, for the nerve fibers fields. In this review, we will analyze the new results regarding the application of NV centers and we will discuss the main challenges that currently prevent these quantum sensors from reaching their full potential., 21 pages, 13 figures

The possibility of using Nitrogen-vacancy centers in diamonds to measure nanoscale magnetic fields with unprecedented sensitivity is one of the most significant achievements of quantum sensing. Here we present an innovative experimental set-up, showing an achieved sensitivity comparable to the state of the art ODMR protocols if the sensing volume is taken into account. The apparatus allows magnetic sensing in biological samples such as individual cells, as it is characterized by a small sensing volume and full bio-compatibility. The sensitivity at different optical powers is studied to extend this technique to the intercellular scale., 6 pages, 5 figures