We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double-Lorentzian noise spectrum consistent with a surface electronic spin bath in the low frequency regime, along with a faster noise source attributed to surface-modified phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks.Nanoscale magnetic imaging and magnetic resonance spectroscopy, recently demonstrated using nitrogenvacancy (NV) color centers in diamond [1][2][3][4], are capable of yielding unique insights into chemistry, biology and physical sciences. The sensitivity and resolution of these techniques relies heavily on the NV coherence properties, which empirically are much worse for shallow NV centers than those deep within bulk diamond [5]. An understanding of the origin of surface related noise enables optimal decoupling or surface passivation to be performed. It is critical not only for improving NV applications in quantum sensing [6,7], quantum information processing [8], and photonics [9], but is also an outstanding problem in many solid-state quantum systems (e.g. [10,11]). Furthermore, overcoming noise at the diamond interface is a significant obstacle to realizing hybrid quantum systems with NV centers [12,13], which are expected to play an important role in realistic devices.For NV centers in bulk diamond, noise sources limiting coherence times have been identified with internal nuclear and electronic spin baths, and interactions with phonons [14,15]. Although additional noise sources related to the diamond surface, and affecting shallow NVs, have been observed [16], their origin is not currently well understood. This phenomenon is general and has been observed at various semiconductor interfaces, resulting in the development of several theoretical models, which are still without significant experimental confirmation [17,18]. Here we use shallow implanted NV centers as nanoscale sensors to perform spectroscopy of the diamond surface. We use dynamical decoupling techniques together with measurements of longitudinal (T 1 ) relaxation under varying conditions (surface coating, magnetic field, temperature) in order to characterize the surface-induced noise. The strength and frequency dependence of fluctuations as a function of the NV distance from the surface are investigated with nanometer precision. We directly measure the noise spectrum experienced by shallow NV centers, revealing an unexpected double-Lorentzian structure which indicates contributions from two distinct noise sources. We find that the low frequency noise experienced by shallow NVs is consistent with electronic spin impurities on the surface [ Fig. 1(a)], w...

Interactions between coinfecting parasites may take various forms, either direct or indirect, facilitative or competitive, and may be mediated by either bottom-up or top-down mechanisms. Although each form of interaction leads to different evolutionary and ecological outcomes, it is challenging to tease them apart throughout the infection period. To establish the first step towards a mechanistic understanding of the interactions between coinfecting limited-term bacterial parasites and lifelong bacterial parasites, we studied the coinfection of Bartonella sp. (limited-term) and Mycoplasma sp. (lifelong), which commonly co-occur in wild rodents. We infected Bartonella-and Mycoplasma-free rodents with each species, and simultaneously with both, and quantified the infection dynamics and host responses. Bartonella benefited from the interaction; its infection load decreased more slowly in coinfected rodents than in rodents infected with Bartonella alone. There were no indications for bottomup effects, but coinfected rodents experienced various changes, depending on the infection stage, in their body mass, stress levels and activity pattern, which may further affect bacterial replication and transmission. Interestingly, the infection dynamics and changes in the average coinfected rodent traits were more similar to the chronic effects of Mycoplasma infection, whereas coinfection uniquely impaired the host's physiological and behavioral stability. These results suggest that parasites with distinct life history strategies may interact, and their interaction may be asymmetric, non-additive, multifaceted and dynamic through time. Because multiple, sometimes contrasting, forms of interactions are simultaneously at play and their relative importance alternates throughout the course of infection, the overall outcome may change under different ecological conditions.

The studies of many-body dynamics of interacting spin ensembles, as well as quantum sensing in solid state systems, are often limited by the need for high spin concentrations, along with efficient decoupling of the spin ensemble from its environment. In particular, for an ensemble of nitrogenvacancy (NV) centers in diamond, high conversion efficiencies between nitrogen (P1) defects and NV centers are essential, while maintaining long coherence times of an NV ensemble. In this work, we study the effect of electron irradiation on the conversion efficiency and the coherence time of various types of diamond samples with different initial nitrogen concentrations. The samples were irradiated using a 200 keV transmission electron microscope (TEM). Our study reveals that the efficiency of NV creation strongly depends on the initial conversion efficiency as well as on the initial nitrogen concentration. The irradiation of the examined samples exhibits an order of magnitude improvement in the NV concentration (up to ∼ 10 11 NV/cm 2 ), without degradation in their coherence times of ∼ 180 µs. We address the potential of this technique toward the study of many-body physics of NV ensembles and the creation of non-classical spin states for quantum sensing. The study of quantum many-body spin physics in realistic solid-state platforms has been a long-standing goal in quantum and condensed-matter physics. In addition to the fundamental understanding of spin dynamics, such research could pave the way toward the demonstration of non-classical spin states, which will be useful for a variety of applications in quantum information and quantum sensing. One of the leading candidates for such studies is the negatively charged nitrogen-vacancy (NV) center in diamond, having unique spin and optical properties, which make it useful for various sensing applications [1][2][3][4][5][6][7][8][9], as well as a resource for quantum information processing and quantum simulation [10][11][12].The current state-of-the-art is limited by the requirement of obtaining high spin concentrations while maintaining long coherence times. The sensitivity of magnetic sensing grows as the square-root of the number of spins [1,3], thus enhanced NV concentrations could improve magnetometric sensitivities. Furthermore, enhanced NV concentrations could lead to strong NV-NV couplings, which together with long coherence times, achieved using a proper dynamical decoupling protocol [13], could pave the way toward the study of many-body dynamics in the NV-NV interaction-dominated regime [10][11][12]. However, nitrogen defects not associated with vacancies (P1 centers) create randomly fluctuating magnetic fields that cause decoherence of the quantum state of the NV ensemble [14,15]. As a result, in most cases it would be beneficial to increase the concentration of NV centers while keeping the nitrogen concentration constant, i.e. improve the N to NV conversion efficiency.A common technique for improving the conversion efficiency is the irradiation of the sample with elec...

Understanding the physical origin of noise affecting quantum systems is important for nearly every quantum application. Quantum noise spectroscopy has been employed in various quantum systems, such as superconducting qubits, NV centers and trapped ions. Traditional spectroscopy methods are usually efficient in measuring noise spectra with mostly monotonically decaying contributions. However, there are important scenarios in which the noise spectrum is broadband and non-monotonous, thus posing a challenge to existing noise spectroscopy schemes. Here, we compare several methods for noise spectroscopy: spectral decomposition based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence, the recently presented DYnamic Sensitivity COntrol (DYSCO) sequence and a modified DYSCO sequence with a Gaussian envelope (gDYSCO). The performance of the sequences is quantified by analytic and numeric determination of the frequency resolution, bandwidth and sensitivity, revealing a supremacy of gDYSCO to reconstruct non-trivial features. Utilizing an ensemble of nitrogen-vacancy centers in diamond coupled to a high density 13 C nuclear spin environment, we experimentally confirm our findings. The combination of the presented schemes offers potential to record high quality noise spectra as a prerequisite to generate quantum systems unlimited by their spin-bath environment.arXiv:1803.07390v3 [quant-ph]

Nitrogen-vacancy (NV) color centers in diamond have been demonstrated as useful magnetic sensors, in particular for measuring spin fluctuations and achieving high sensitivity and spatial resolution. These abilities can be used to explore various biological and chemical processes, catalyzed by reactive oxygen species (ROS). Here we demonstrate a novel approach to measure and quantify hydroxyl radicals with high spatial resolution, using the fluorescence difference between NV charged states. According to the results, the achieved NV sensitivity is ± 11 4 nM Hz , realized in situ without spin labels and localized to a volume of ∼10 picoliters.