Quantum Optics INRIM

Color centers in diamond

Color centers in diamond are quantum systems with a great applicability in many interdisciplinary fields. One important example is the Nitrogen-Vacancy (NV) center, whose photo-emission and electron-spin resonance properties even at room temperature have allowed the demonstration of its capabilities as reliable solid-state single-photon emitter and quantum sensor.

In our labs, featuring 3 Single-photon-sensitive confocal microscopes, we study, in collaboration with University of Turin, the properties of color centers at room temperature and in cryogenic conditions (having demonstrated single-photon emission by novel centers [1] related He, Sn, Pb, F, etc), contributing to the quest for the ideal, on-demand single-photon source (SPS) of practical interest in the emerging quantum technologies. We are actively involved in the efforts for the standardization of these quantum objects[2] and we exploit the nonclassicalproperties of SPSs to perform quantum enhanced measurements [3].

In recent years, our research scope has broadened to include the sensing of magnetic field [4] and temperature [5] in biological systems exploiting the fact that NV centres are  optically addressable and coherently controllable by microwaves even at room temperature and can be used as quantum sensors. We discovered that working in a  “tranverse field regime”  lead to an increase in the sensitivity of a temperature measurement.  We are investigating the  possibility of sensing magnetic field of biological origin and temperature changes related to physiological process inside  the cell.  We have measured temperature changes related to action potential propagation metabolic effects inside a single neuron and we are now extending these techniques.

Recent highlights

A biocompatible technique for magnetic field sensing at (sub)cellular scale using Nitrogen-Vacancy centers

E. Bernardi et al. EPJ Quantum Technology 7, 13 (2020)

We present an innovative experimental set-up that uses Nitrogen-Vacancy centres in diamonds to measure magnetic fields with the sensitivity of η=68±3 nT/√Hz at demonstrated (sub)cellular scale. The presented method of magnetic sensing, utilizing a lock-in based ODMR technique for the optical detection of microwave-driven spin resonances induced in NV centers, is characterized by the excellent magnetic sensitivity at such small scale and the full biocompatibility. The cellular scale is obtained using a NV-rich sensing layer of 15 nm thickness along z axis and a focused laser spot of (10×10) μm2 in x-y plane. The biocompatibility derives from an accurate choice of the applied optical power. For this regard, we also report how the magnetic sensitivity changes for different applied laser power and discuss the limits of the sensitivity sustainable with biosystem at such small volume scale. As such, this method offers a whole range of research possibilities for biosciences. 

Nanodiamond–Quantum Sensors Reveal Temperature Variation Associated to Hippocampal Neurons Firing

G.Petrini et al., Adv. Sci. (2022) 2202014

Temperature is one of the most relevant parameters for the regulation ofintracellular processes. Measuring localized subcellular temperature gradientsis fundamental for a deeper understanding of cell function, such as thegenesis of action potentials, and cell metabolism. Notwithstanding severalproposed techniques, at the moment detection of temperature fluctuations atthe subcellular level still represents an ongoing challenge. Here, for the firsttime, temperature variations (1°C) associated with potentiation and inhibitionof neuronal firing is detected, by exploiting a nanoscale thermometer basedon optically detected magnetic resonance in nanodiamonds. The resultsdemonstrate that nitrogen-vacancy centers in nanodiamonds provide a toolfor assessing various levels of neuronal spiking activity, since they are suitablefor monitoring different temperature variations, respectively, associated withthe spontaneous firing of hippocampal neurons, the disinhibition ofGABAergic transmission and the silencing of the network. Conjugated withthe high sensitivity of this technique (in perspective sensitive to<0.1°Cvariations), nanodiamonds pave the way to a systematic study of thegeneration of localized temperature gradients under physiological andpathological conditions. Furthermore, they prompt further studies explainingin detail the physiological mechanism originating this effect.

Most relevant pubblications

[1] S. Ditalia Tchernij,  et al. "Single-photon emitters in lead-implanted single-crystal diamond" ACS Photonics 5 (12), 4864 – 4871 (2018), journal cover.

[2] E. Moreva, et al., "Feasibility study towards comparison of the g(2)(0) measurement in the visible range", Metrologia 56, 015016 (2019).

[3] D. Gatto Monticone, et al. "Beating the Abbe diffraction limit in confocal microscopy via non classical photon statistics", Phys. Rev. Lett. 113 (14), 143602 (2014).

[4] Bernardi, Ettore, et al. "A biocompatible technique for magnetic field sensing at (sub) cellular scale using Nitrogen-Vacancy centers." EPJ Quantum Technology 7, 13 (2020).

[5] Moreva, E., et al. "Practical applications of quantum sensing: A simple method to enhance the sensitivity of nitrogen-vacancy-based temperature sensors." Physical Review Applied 13, 054057 (2020) 

[6] G.Petrini et al. "Nanodiamond–Quantum Sensors Reveal Temperature Variation Associated to Hippocampal Neurons Firing", Adv. Sci. (2022) 2202014