Abstract
Diamond defect centers are promising solid state magnetometers. Single centers allow for high spatial resolution field imaging but are limited in their magnetic field sensitivity to around 10 nT/Hz^(1/2) at room-temperature. Using defect center ensembles sensitivity can be scaled as N^(1/2) when N is the number of defects. In the present work we use an ensemble of 1e11 defect centers for sensing. By carefully eliminating all noise sources like laser intensity fluctuations, microwave amplitude and phase noise we achieve a photon shot noise limited field sensitivity of 0.9 pT/Hz^(1/2) at room-temperature with an effective sensor volume of 8.5e-4 mm^3. The smallest field we measured with our device is 100 fT. While this denotes the best diamond magnetometer sensitivity so far, further improvements using decoupling sequences and material optimization could lead to fT/Hz^(1/2) sensitivity.
Highlights
Nitrogen-vacancy (NV) defect centers in diamond are promising solid-state magnetometers
Superconducting quantum-interference devices (SQUID) [5] and atomic vapor cells [6] are at the forefront of magnetic sensitivities, and they explore the limits for detection of fundamental flux quantization
We have applied ac magnetometry based on spin-echo techniques, which suppresses lowfrequency noise
Summary
Magnetic sensors find application in various areas of science, technology, and medicine [1,2]. [25], repetitive readout [26,27], or different detection schemes [28,29] Since both fluorescence signal and spin projectionpaffiffirffie sources of uncorrelated noise, sensitivity scales as n over a wide range of measurement times, where n is the number of individual sensor readouts. This estimate relies on the assumption that the results of single readout steps show a normal distribution around a constant mean value (central-limit theorem) This condition is usually met for measurements on single NV centers with comparably small numbers of total signal photons dominated by optical shot noise or spin projection noise—a frequency-independent, uncorrelated white-noise background. Nuclear-spin-assisted repetitive readout [26], infrared-absorption-based readout [28], or enhancement by optical cavities [29] are strategies to reach the projection noise limit
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