Nuclear magnetic resonance (NMR) spectroscopy is a key analytical technique in chemistry, biology, and medicine. However, conventional NMR spectroscopy requires an at least nanoliter-sized sample volume to achieve sufficient signal. We combined the use of a quantum memory and high magnetic fields with a dedicated quantum sensor based on nitrogen vacancy centers in diamond to achieve chemical shift resolution in H andF NMR spectroscopy of 20-zeptoliter sample volumes. We demonstrate the application of NMR pulse sequences to achieve homonuclear decoupling and spin diffusion measurements. The best measured NMR linewidth of a liquid sample was ~1 part per million, mainly limited by molecular diffusion. To mitigate the influence of diffusion, we performed high-resolution solid-state NMR by applying homonuclear decoupling and achieved a 20-fold narrowing of the NMR linewidth.

Newly discovered van der Waals materials like MoS, WSe, hexagonal boron nitride (h-BN), and recently CN have sparked intensive research to unveil the quantum behavior associated with their 2D structure. Of great interest are 2D materials that host single quantum emitters. h-BN, with a band gap of 5.95 eV, has been shown to host single quantum emitters which are stable at room temperature in the UV and visible spectral range. In this paper we investigate correlations between h-BN structural features and emitter location from bulk down to the monolayer at room temperature. We demonstrate that chemical etching and ion irradiation can generate emitters in h-BN. We analyze the emitters' spectral features and show that they are dominated by the interaction of their electronic transition with a single Raman active mode of h-BN. Photodynamics analysis reveals diverse rates between the electronic states of the emitter. The emitters show excellent photo stability even under ambient conditions and in monolayers. Comparing the excitation polarization between different emitters unveils a connection between defect orientation and the h-BN hexagonal structure. The sharp spectral features, color diversity, room-temperature stability, long-lived metastable states, ease of fabrication, proximity of the emitters to the environment, outstanding chemical stability, and biocompatibility of h-BN provide a completely new class of systems that can be used for sensing and quantum photonics applications.

Photonic structures in diamond are key to most of its application in quantum technology. Here, we demonstrate tapered nano-waveguides structured directly onto the diamond substrate hosting shallow-implanted nitrogen vacancy (NV) centers. By optimization based on simulations and precise experimental control of the geometry of these pillar-shaped nano-waveguides, we achieve a net photon flux up to ~ 1.7 × 10 6 /s. This presents the brightest monolithic bulk diamond structure based on single NV centers so far. We observe no impact on excited state lifetime and electronic spin dephasing time (T 2 ) due to the nanofabrication process. Possessing such high brightness with low background in addition to preserved spin quality, this geometry can improve the current nanomagnetometry sensitivity ~ 5 times. In addition, it facilitates a wide range of diamond defects-based magnetometry applications. As a demonstration, we measure the temperature dependency of T 1 relaxation time of a single shallow NV center electronic spin. We observe the two-phonon Raman process to be negligible in comparison to the dominant two-phonon Orbach process. KEYWORDS: shallow nitrogen vacancy center, diamond tapered nanopillar, nanofabrication, T 2 dephasing time, low temperature T 1 relaxation timeDiamond defect centers are exquisite nanoscale sensors for a variety of physical parameters like magnetic 1 and electric 2 fields and temperature 3 . Among other parameters their sensitivity relies on proximity and photon detection efficiency. Nuclear magnetic resonance (NMR) experiments were recently shown 4-8 using the negatively-charged nitrogen vacancy (NV) center positioned few nanometers below the diamond surface ("shallow" NV center). These experiments became possible by the ability to optically address and readout spins of the NV center 9 . Yet, a major drawback of all magnetometry-based experiments with shallow NV centers is the low number of collected photons which causes long measurement times. At the same time, the photon count rate (F) also limits the magnetometry sensitivity 10 as it scales with1/√F.A major reason for the low signal strength is the high refractive index mismatch 11 between diamond (n diamond ~ 2.4) and the collection medium (e.g. air; n air ~ 1). This causes most of the emitted photons from the NV center to be reflected back at the diamond-air interface into the diamond substrate. Even by benefiting from high NA microscope objective lenses, collection efficiencies are typically 12 below 10% resulting in total instrument detection efficiency on the order of 1%. Recently, efforts have been made to overcome this drawback by fabricating photonic structures directly onto the diamond surface in order to enhance the collection efficiency of either deep [12][13][14][15][16][17] or shallow NV centers 18 . Maletinsky et al. 18 demonstrated a monolithic diamond scanning tip based on nanopillars hosting NV centers ~ 10 nm below the nanopillars top surface. Such tips were fabricated from diamond nanopillars with a uniform di...

Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometre positioning accuracy, which is typically achieved by low-energy ion implantation. A drawback of this technique is the significant residual lattice damage, which degrades the performance of spins in quantum applications. Here we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. Charging of vacancies at, for example, nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in tenfold-improved spin coherence times and twofold-improved formation yield of nitrogen-vacancy centres in diamond. This is achieved by confining implantation defects into the space-charge layer of free carriers generated by a boron-doped diamond structure. By combining these results with numerical calculations, we arrive at a quantitative understanding of the formation and dynamics of the implanted spin defects. These results could improve engineering of quantum devices using solid-state systems.