Sensing electric fields using single diamond spins

The ability to sensitively detect charges under ambient conditions would be a fascinating new tool benefitting a wide range of researchers across disciplines. However, most current techniques are limited to low-temperature methods like single-electron transistors (SET), single-electron electrostatic force microscopy and scanning tunnelling microscopy. Here we open up a new quantum metrology technique demonstrating precision electric field measurement using a single nitrogen-vacancy defect centre(NV) spin in diamond. An AC electric field sensitivity reaching ~ 140V/cm/\surd Hz has been achieved. This corresponds to the electric field produced by a single elementary charge located at a distance of ~ 150 nm from our spin sensor with averaging for one second. By careful analysis of the electronic structure of the defect centre, we show how an applied magnetic field influences the electric field sensing properties. By this we demonstrate that diamond defect centre spins can be switched between electric and magnetic field sensing modes and identify suitable parameter ranges for both detector schemes. By combining magnetic and electric field sensitivity, nanoscale detection and ambient operation our study opens up new frontiers in imaging and sensing applications ranging from material science to bioimaging

Room temperature coherent control of coupled single spins in solid

Coherent coupling between single quantum objects is at the heart of modern quantum physics. When coupling is strong enough to prevail over decoherence, it can be used for the engineering of correlated quantum states. Especially for solid-state systems, control of quantum correlations has attracted widespread attention because of applications in quantum computing. Such coherent coupling has been demonstrated in a variety of systems at low temperature1, 2. Of all quantum systems, spins are potentially the most important, because they offer very long phase memories, sometimes even at room temperature. Although precise control of spins is well established in conventional magnetic resonance3, 4, existing techniques usually do not allow the readout of single spins because of limited sensitivity. In this paper, we explore dipolar magnetic coupling between two single defects in diamond (nitrogen-vacancy and nitrogen) using optical readout of the single nitrogen-vacancy spin states. Long phase memory combined with a defect separation of a few lattice spacings allow us to explore the strong magnetic coupling regime. As the two-defect system was well-isolated from other defects, the long phase memory times of the single spins was not diminished, despite the fact that dipolar interactions are usually seen as undesirable sources of decoherence. A coherent superposition of spin pair quantum states was achieved. The dipolar coupling was used to transfer spin polarisation from a nitrogen-vacancy centre spin to a nitrogen spin, with optical pumping of a nitrogen-vacancy centre leading to efficient initialisation. At the level anticrossing efficient nuclear spin polarisation was achieved. Our results demonstrate an important step towards controlled spin coupling and multi-particle entanglement in the solid state

COPD patients' ability to follow exercise influences short-term outcomes of rehabilitation

Chronic obstructive pulmonary disease (COPD) patients with limited ability to follow exercise protocols may receive smaller benefits from rehabilitation. The association between the ability to follow exercise protocols and short-term outcomes of rehabilitation was assessed in COPD patients. As a measure of the ability to follow exercise protocols, the number of major breaks lasting >or=1 min was determined in 98 COPD patients during supervised exercise sessions. The benefits from rehabilitation were compared between patients with, on average, more than one and one or fewer major breaks per session. Patients with one or fewer major breaks per session showed significantly greater improvements in exercise capacity (between-groups difference of 38 m for 6-min walking distance, 22.1 W for short-time maximum exercise capacity (steep ramp test) and 5.5 W for maximum exercise capacity). Quality of life also tended to be better in patients with one or fewer major breaks per session, but the differences were nonsignificant (adjusted between-groups difference in Chronic Respiratory Disease Questionnaire total score of 0.14). Limited ability to follow exercise protocols is associated with smaller benefits of rehabilitation. This finding highlights the importance of choosing tolerable exercise protocols for chronic obstructive pulmonary disease patients