The Role of Electrolytes in the Relaxation of Near-Surface Spin Defects in Diamond

Abstract

Quantum sensing with spin defects in diamond, such as the nitrogen vacancy (NV) center, enables the detection of various chemical species on the nanoscale. Molecules or ions with unpaired electronic spins are typically probed by their influence on the NV center’s spin relaxation. Whereas it is well-known that paramagnetic ions reduce the NV center’s relaxation time (T 1), here we report on the opposite effect for diamagnetic ions. We demonstrate that millimolar concentrations of aqueous diamagnetic electrolyte solutions increase the T 1 time of near-surface NV center ensembles compared to pure water. To elucidate the underlying mechanism of this surprising effect, single and double quantum NV experiments are performed, which indicate a reduction of magnetic and electric noise in the presence of diamagnetic electrolytes. In combination with ab initio simulations, we propose that a change in the interfacial band bending due to the formation of an electric double layer leads to a stabilization of fluctuating charges at the interface of an oxidized diamond. This work not only helps to understand noise sources in quantum systems but could also broaden the application space of quantum sensors toward electrolyte sensing in cell biology, neuroscience, and electrochemistry.

Quantum sensing of microRNAs with nitrogen-vacancy centers in diamond

“…Since the excitation power intensity (9 kW cm −2 ) used is below saturation (~100 kW cm −2 ) 48 and surface oxygenation stabilizes shallow negatively charged NVs 49 , effects attributed to NVs charge conversion are neglected in this work. Moreover, concentration of 10 mM of diamagnetic NaCl used in the presented measurements has been shown not to affect T 1 46 . Furthermore, we test if charged miR-21 adsorbates induce observable electric noise by measuring the change in spin relaxation contrast with no Mn ions present (see Supplementary Fig.…”

“…It has been shown that spin relaxation measurements, apart from temperature, can also be susceptible to NV centers charge conversion (induced by laser excitation) 45 , diamagnetic electrolyte solutions 46 and electric noise 29 , 47 . Since the excitation power intensity (9 kW cm −2 ) used is below saturation (~100 kW cm −2 ) 48 and surface oxygenation stabilizes shallow negatively charged NVs 49 , effects attributed to NVs charge conversion are neglected in this work.…”

Photo‐Induced Charge State Dynamics of the Neutral and Negatively Charged Silicon Vacancy Centers in Room‐Temperature Diamond

“…Adding to the results in Figure 1d , the solid circles and lines in Figure 3c respectively show the relative SiV − fluorescence as a function of time for λ IR = 750 nm and the calculated fits using Equation 3 assuming r 0 = 1 nm, as seen for NV centers; [ 36 ] in all cases, we set the nitrogen concentration at 3 ppm, consistent with prior observations in this same sample crystal. [ 22 ] Comparison between the measured and calculated SiV response shows good agreement (see also Section S2 , Supporting Information for the complete data set).…”

Room Temperature Relaxometry of Single Nitrogen Vacancy Centers in Proximity to α-RuCl3 Nanoflakes

“…It has been observed that a diamagnetic electrolyte near the NV center reduces both electric and magnetic noise, consequently improving T 1 . A theoretical calculation for the T 1 relaxation time of an NV center proximate to a 2D spin liquid shows similar effects of a diamagnetic state on the T 1 .…”