Quantum Error Correction for Metrology

We propose and analyze a new approach based on quantum error correction (QEC) to improve quantum metrology in the presence of noise. We identify the conditions under which QEC allows one to improve the signal-to-noise ratio in quantum-limited measurements, and we demonstrate that it enables, in certain situations, Heisenberg-limited sensitivity. We discuss specific applications to nanoscale sensing using nitrogen-vacancy centers in diamond in which QEC can significantly improve the measurement sensitivity and bandwidth under realistic experimental conditions.Chemistry and Chemical BiologyPhysic

Magnetic resonance spectroscopy of an atomically thin material using a single-spin qubit

Two-dimensional (2D) materials offer a promising platform for exploring condensed matter phenomena and developing technological applications. However, the reduction of material dimensions to the atomic scale poses a challenge for traditional measurement and interfacing techniques that typically couple to macroscopic observables. We demonstrate a method for probing the properties of 2D materials via nanometer-scale nuclear quadrupole resonance (NQR) spectroscopy using individual atom-like impurities in diamond. Coherent manipulation of shallow nitrogen-vacancy (NV) color centers enables the probing of nanoscale ensembles down to ∼30 nuclear spins in atomically thin hexagonal boron nitride (h-BN). The characterization of low-dimensional nanoscale materials could enable the development of new quantum hybrid systems, combining atom-like systems coherently coupled with individual atoms in 2D materials.Chemistry and Chemical BiologyPhysic

NMR technique for determining the depth of shallow nitrogen-vacancy centers in diamond

We demonstrate a robust experimental method for determining the depth of individual shallow nitrogen-vacancy (NV) centers in diamond with ∼1 nm uncertainty. We use a confocal microscope to observe single NV centers and detect the proton nuclear magnetic resonance (NMR) signal produced by objective immersion oil, which has well understood nuclear spin properties, on the diamond surface. We determine the NV center depth by analyzing the NV NMR data using a model that describes the interaction of a single NV center with the statistically polarized proton spin bath. We repeat this procedure for a large number of individual, shallow NV centers and compare the resulting NV depths to the mean value expected from simulations of the ion implantation process used to create the NV centers, with reasonable agreement.Physic

Nanoscale NMR spectroscopy and imaging of multiple nuclear species

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) provide non-invasive information about multiple nuclear species in bulk matter, with wide-ranging applications from basic physics and chemistry to biomedical imaging1. However, the spatial resolution of conventional NMR and MRI is limited2 to several micrometres even at large magnetic fields (>1 T), which is inadequate for many frontier scientific applications such as single-molecule NMR spectroscopy and in vivo MRI of individual biological cells. A promising approach for nanoscale NMR and MRI exploits optical measurements of nitrogen–vacancy (NV) colour centres in diamond, which provide a combination of magnetic field sensitivity and nanoscale spatial resolution unmatched by any existing technology, while operating under ambient conditions in a robust, solid-state system3, 4, 5. Recently, single, shallow NV centres were used to demonstrate NMR of nanoscale ensembles of proton spins, consisting of a statistical polarization equivalent to ∼100–1,000 spins in uniform samples covering the surface of a bulk diamond chip6, 7. Here, we realize nanoscale NMR spectroscopy and MRI of multiple nuclear species (1H, 19F, 31P) in non-uniform (spatially structured) samples under ambient conditions and at moderate magnetic fields (∼20 mT) using two complementary sensor modalities.Physic

Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic

Nuclear magnetic resonance spectroscopy is a powerful tool for the structural analysis of organic compounds and biomolecules but typically requires macroscopic sample quantities. We use a sensor, which consists of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface-treatment technique to extend the spin coherence time of shallow nitrogen-vacancy centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within 1 second of integration. This gain in sensitivity enables high-confidence detection of individual proteins and allows us to observe spectral features that reveal information about their chemical composition.Physic