The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high-quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen–vacancy centre spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen–vacancy spin–strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen–vacancy centre. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen–vacancy ground-state spin. The nitrogen–vacancy centre is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 × 10−6 strain Hz−1/2. Finally, we show how this spin-resonator system could enable coherent spin–phonon interactions in the quantum regime.

We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 - 100 nm display long spin coherence times, T2 > 100 \mus at d = 5 nm and T2 > 600 \mus at d \geq 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.Comment: 14 pages, 4 figures, 11 pages of additional supplementary materia

Sensitive nanoscale magnetic resonance imaging (MRI) of target spins using nitrogen--vacancy (NV) centers in diamond will require a quantitative understanding of dominant noise at the surface. We probe this noise by applying dynamical decoupling to shallow NVs at calibrated depths. Results support a model of NV dephasing by a surface bath of electronic spins having a correlation rate of 200 kHz, much faster than that of the bulk N spin bath. Our method of combining nitrogen delta--doping growth and nanoscale depth imaging paves a way for studying spin noise present in diverse material surfaces.The negatively charged nitrogen--vacancy (NV) center in diamond is a robust quantum sensor of magnetic fields [1--4]. Although an individual NV has the capability to detect small numbers of electronic [5--7] and nuclear spins external to diamond [8--10], its widespread application in spin imaging has been limited by the ability to form shallow NVs that retain spin coherence near the surface. Shallow spins with long coherence time, T 2 , are important because quantum phase accumulation between two electronic spin states of the NV provides signal transduction, and hence the minimum detectable magnetic dipole moment scales as δµ ∝ r 3 / T 2 , with r the NV--target spin distance [3,4]. At odds with this figure of merit is strong evidence that the diamond crystal surface adversely affects T 2 , reducing it from ~2 ms for bulk NVs [11,12] to less than 10 µs for few--nm deep NVs [6,13--16], but the origin of this decoherence is an outstanding question. We consider in this letter a model of surface spin induced decoherence, a theory which has emerged from experiments on other systems [20,21] where long coherence is a requirement, such as in superconducting circuits [17,18] and spin

We probe the relaxation dynamics of the full three-level spin system of near-surface nitrogenvacancy (NV) centers in diamond to define a T1 relaxation time that helps resolve the T2 ≤ 2T1 coherence limit of the NV's subset qubit superpositions. We find that double-quantum spin relaxation via electric field noise dominates T1 of near-surface NVs at low applied magnetic fields. Furthermore, we differentiate 1/f α spectra of electric and magnetic field noise using a novel noisespectroscopy technique, with broad applications in probing surface-induced decoherence at material interfaces.