Optimized quantum sensing with a single electron spin using real-time adaptive measurements.

Quantum sensors based on single solid-state spins promise a unique combination of sensitivity and spatial resolution. The key challenge in sensing is to achieve minimum estimation uncertainty within a given time and with high dynamic range. Adaptive strategies have been proposed to achieve optimal performance, but their implementation in solid-state systems has been hindered by the demanding experimental requirements. Here, we realize adaptive d.c. sensing by combining single-shot readout of an electron spin in diamond with fast feedback. By adapting the spin readout basis in real time based on previous outcomes, we demonstrate a sensitivity in Ramsey interferometry surpassing the standard measurement limit. Furthermore, we find by simulations and experiments that adaptive protocols offer a distinctive advantage over the best known non-adaptive protocols when overhead and limited estimation time are taken into account. Using an optimized adaptive protocol we achieve a magnetic field sensitivity of 6.1 ± 1.7 nT Hz(-1/2) over a wide range of 1.78 mT. These results open up a new class of experiments for solid-state sensors in which real-time knowledge of the measurement history is exploited to obtain optimal performance.

Integrated high-quality factor optical resonators in diamond.

The realization of an integrated diamond photonic platform, based on a thin single crystal diamond film on top of a silicon dioxide/silicon substrate, is reported. Using this approach, we demonstrate high-quality factor single crystal diamond race-track resonators, operating at near-infrared wavelengths (1550 nm). The devices are integrated with low-loss diamond waveguides terminated with polymer pads (spot size converters) to facilitate in- (out-) coupling of light from (to) an optical fiber. Optical characterization of these resonators reveal quality factors as high as ~250,000 and overall insertion losses as low as 1 dB/facet. Scattering induced mode splitting as well as signatures of nonlinear effects such as optical bistability are observed at an input pump power of ~100 mW in the waveguides.

High-dynamic-range magnetometry with a single nuclear spin in diamond.

Sensors based on the nitrogen-vacancy defect in diamond are being developed to measure weak magnetic and electric fields at the nanoscale. However, such sensors rely on measurements of a shift in the Lamor frequency of the defect, so an accumulation of quantum phase causes the measurement signal to exhibit a periodic modulation. This means that the measurement time is either restricted to half of one oscillation period, which limits accuracy, or that the magnetic field range must be known in advance. Moreover, the precision increases only slowly (as T(-0.5)) with measurement time T (ref. 3). Here, we implement a quantum phase estimation algorithm on a single nuclear spin in diamond to combine both high sensitivity and high dynamic range. By achieving a scaling of the precision with time to T(-0.85), we improve the sensitivity by a factor of 7.4 for an accessible field range of 16 mT, or, alternatively, we improve the dynamic range by a factor of 130 for a sensitivity of 2.5 µT Hz(-1/2). Quantum phase estimation algorithms have also recently been implemented using a single electron spin in a nitrogen-vacancy centre. These methods are applicable to a variety of field detection schemes, and do not require quantum entanglement.

Chemical vapour deposition synthetic diamond: materials, technology and applications.

Substantial developments have been achieved in the synthesis of chemical vapour deposition (CVD) diamond in recent years, providing engineers and designers with access to a large range of new diamond materials. CVD diamond has a number of outstanding material properties that can enable exceptional performance in applications as diverse as medical diagnostics, water treatment, radiation detection, high power electronics, consumer audio, magnetometry and novel lasers. Often the material is synthesized in planar form; however, non-planar geometries are also possible and enable a number of key applications. This paper reviews the material properties and characteristics of single crystal and polycrystalline CVD diamond, and how these can be utilized, focusing particularly on optics, electronics and electrochemistry. It also summarizes how CVD diamond can be tailored for specific applications, on the basis of the ability to synthesize a consistent and engineered high performance product.