Ref HAL: hal-03837709_v1
Ref Arxiv: 2210.05485
Ref INSPIRE: 2164234
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We report successful incorporation of an ensemble of G centers in silicon-on-insulator (SOI) microrings using ion implantation and conventional nanofabrication. The coupling between the emitters and the resonant modes of the microrings is studied using continuous-wave and time-resolved microphotoluminescence (PL) experiments. We observe the resonant modes of the microrings on PL spectra, on the wide spectral range that is covered by G centers emission. By finely tuning the size of the microrings, we match their zero-phonon line at 1278 nm with a resonant mode of quality factor around 3000 and volume 7.2 (lambda over n)^3. The zero-phonon line intensity is enhanced by a factor of 5, both in continuous-wave and time-resolved measurements. This is attributed to the Purcell enhancement of zero-phonon spontaneous emission into the resonant mode and quantitatively understood considering the distribution of the G centers dipoles. Despite the enhancement of the zero-phonon emission, we do not observe any sizeable decrease of the average lifetime of the G centers, which points at a low radiative yield (<10%). We reveal the detrimental impact of parasitic defects in heavily implanted silicon, and discuss the perspectives for quantum electrodynamics experiments with individual color centers in lightly implanted SOI rings. Our results provide key information for the development of deterministic single photon sources for integrated quantum photonics.

Ref HAL: hal-03715989_v1
DOI: 10.1016/j.carbon.2022.04.005
WoS: WOS:000802226300010
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In this work we investigate the properties of negatively charged nitrogen-vacancy (NV−) centres created during single crystal diamond growth by chemical vapour deposition (CVD) on [113]-oriented substrates and with N2O as a dopant gas. The use of spin echo and double electron-electron resonance (DEER) allows us to assess NV− ratio with respect to substitutional nitrogen impurities (N_S0) incorporated during growth, a critical figure of merit for quantum technologies. We demonstrate that, at moderate growth temperatures (800 °C), dense NV− ensembles of several hundreds of ppb (800 ppb for 50 ppm of added N2O) and with exceptionally high NV−/N_S0 ratios of up to 25% can be achieved. This NV− creation yield is higher by at least an order of magnitude to that typically obtained on standard [100]-grown diamonds and comparable to the best values reported for electron-irradiated diamonds. The material obtained here thus advantageously combines a high NV− density, high creation yield, long coherence times of several tens of μs together with a partial preferential orientation. These are highly desirable requirements for diamond-based quantum sensors that may spur new developments with this crystalline orientation leading to improved performance and sensitivity.

Ref HAL: hal-03656679_v1
DOI: 10.1103/physrevapplied.17.044051
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BiFeO3 is a rich room-temperature multiferroic material in which noncollinear antiferromagnetic spin cycloids can be deterministically controlled by an electric field through the magnetoelectric interaction, opening perspectives for low-power reconfigurable antiferromagnetic spintronics. Using a commercial scanning nitrogen-vacancy (N-V) magnetometer, we are able to image two different types of spin cycloids stabilized in strain-engineered BiFeO3 epitaxial thin films. We show that, in these samples harboring two ferroelectric variants, each ferroelectric domain is coupled to a single spin cycloid, giving rise to a zigzag magnetic pattern. These ferroelectric domains can be manipulated at the local scale by piezoresponse force microscopy, allowing the design of micron-sized single domains. Thanks to its coupled optical microscope and fast-imaging capabilities, the scanning N-V magnetometer enables a quick repositioning in such areas of interest. Finally, quantitative imaging on single ferroelectric domains provides insights into the physical parameters of each spin-cycloid type and their impact on the magnetic-stray-field measurements.

Ref HAL: hal-03677973_v1
Ref Arxiv: 2105.08075
Ref INSPIRE: 2079933
DOI: 10.1103/PhysRevLett.128.177401
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We investigate the magnetic field dependent photo-physics of individual Nitrogen-Vacancy (NV) color centers in diamond under cryogenic conditions. At distinct magnetic fields, we observe significant reductions in the NV photoluminescence rate, which indicate a marked decrease in the optical readout efficiency of the NV's ground state spin. We assign these dips to excited state level anti-crossings, which occur at magnetic fields that strongly depend on the effective, local strain environment of the NV center. Our results offer new insights into the structure of the NVs' excited states and a new tool for their effective characterization. Using this tool, we observe strong indications for strain-dependent variations of the NV's orbital g-factor, obtain new insights into NV charge state dynamics, and draw important conclusions regarding the applicability of NV centers for low-temperature quantum sensing.

Ref HAL: hal-03659802_v1
DOI: 10.1103/PhysRevLett.128.187201
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We report on the formation of topological defects emerging from the cycloidal antiferromagnetic order at the surface of bulk BiFeO3 crystals. Combining reciprocal and real-space magnetic imaging techniques, we first observe, in a single ferroelectric domain, the coexistence of antiferromagnetic domains in which the antiferromagnetic cycloid propagates along different wave vectors. We then show that the direction of these wave vectors is not strictly locked to the preferred crystallographic axes as continuous rotations bridge different wave vectors. At the junctions between the magnetic domains, we observe topological line defects identical to those found in a broad variety of lamellar physical systems with rotational symmetries. Our work establishes the presence of these magnetic objects at room temperature in the multiferroic antiferromagnet BiFeO3, offering new possibilities for their use in spintronics

Ref HAL: hal-03662870_v1
DOI: 10.3917/rdes.099.0010
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Ref HAL: hal-03295925_v1
DOI: 10.1103/PhysRevB.103.235418
WoS: WOS:000662302900006
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The nitrogen-vacancy (NV) defect in diamond is an efficient quantum sensor of randomly fluctuating signalsvia relaxometry measurements. In particular, the longitudinal spin relaxation of the NV defect accelerates in thepresence of magnetic noise with a spectral component at its electron spin resonance frequency.We look into thiseffect quantitatively by applying a calibrated and tunable magnetic noise on a single NV defect.We show that anincrease of the longitudinal spin relaxation rate translates into a reduction of the photoluminescence (PL) signalemitted under continuous optical illumination, which can be explained using a simplified three-level model of theNV defect. This PL quenching mechanism offers a simple, all-optical method to detect magnetic noise sourcesat the nanoscale.