High-dynamic-range magnetometry with a single electronic spin in diamond

Abstract

Magnetic sensors capable of detecting nanoscale volumes of spins allow for non-invasive, element-specific probing. The error in such measurements is usually reduced by increasing the measurement time, and noise averaging the signal. However, achieving the best precision requires restricting the maximum possible field strength to much less than the spectral linewidth of the sensor. Quantum entanglement and squeezing can then be used to improve precision (although they are difficult to implement in solid-state environments). When the field strength is comparable to or greater than the spectral linewidth, an undesirable trade-off between field strength and signal precision occurs. Here, we implement novel phase estimation algorithms on a single electronic spin associated with the nitrogen-vacancy defect centre in diamond to achieve an ∼8.5-fold improvement in the ratio of the maximum field strength to precision, for field magnitudes that are large (∼0.3 mT) compared to the spectral linewidth of the sensor (∼4.5 µT). The field uncertainty in our approach scales as 1/T(0.88), compared to 1/T(0.5) in the standard measurement approach, where T is the measurement time. Quantum phase estimation algorithms have also recently been implemented using a single nuclear spin in a nitrogen-vacancy centre. Besides their direct impact on applications in magnetic sensing and imaging at the nanoscale, these results may prove useful in improving a variety of high-precision spectroscopy techniques.

A scanning superconducting quantum interference device with single electron spin sensitivity

“…Remarkably, the ø46 nm SOT reaches sensitivity of 0.38 µ B /Hz 1/2 that represents more than two orders of magnitude improvement 4,5,12 over any previously reported SQUIDs. Moreover, in sharp contrast to conventional SQUIDs and a number of recent optical readout magnetometers that can operate only at low fields [21][22][23][24][25] , the SOTs can operate and remain very sensitive also at high fields. The ø56 and the ø46 nm Pb SOTs display spin noise of 0.75 and 0.6 µ B /Hz 1/2 , respectively, at an unprecedented field of 1 T.…”

Dual-channel lock-in magnetometer with a single spin in diamond

“…See SI Fig. S3 for description of the Bayesian estimation process [37][38][39] .The data in Fig. 2(c) shows that our PEA unambiguously measures the value of the magnetic field with a linear readout over a wide range, and is also able to resolve phase shifts of π.…”

“…where V ∼ 0.3 is the fringe visibility, and ξ is a factor that depends on the photon collection efficiency in our system 6,37 . Through prior knowledge of the working point, it is assumed that nφ I ≈ 2mπ and this requirement will be more stringent as n increases 6 .…”

Optimizing phase-estimation algorithms for diamond spin magnetometry

“…13 , a static magnetic field of 40 mT is applied along the NV axis by a permanent magnet. Level anti-crossing (LAC) occurs between the |m S = −1 and |m S = 0 sublevels in the excited state, which results in dynamic nuclear-spin polarization (DNP) of 14 N nuclear spin (I=1) associated with most NV experiments 18 .…”

“…Our theoretical simulations below assume typical numbers from the experiments of Ref. 13 , but we shall discuss the consequences of improved experimental efficiency where appropriate. For clarity, we shall use the notations |0 ≡ |m S = 0 and |1 ≡ |m S = −1 to describe the qubit basis states from here onwards.…”