Ref HAL: hal-04258263_v1
DOI: 10.1140/epjd/s10053-022-00528-x
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We employ the electronic spin of a single nitrogen-vacancy (NV) defect in diamond to detect and control the quantum state of remote nuclear spins coupled by hyperfine interaction. More precisely, our work focuses on individual 13C nuclei featuring a moderate hyperfine coupling strength (∼ 1 MHz) with the NV’s electron spin. Two different methods providing an efficient room-temperature polarization of these peculiar 13C nuclear spins are described. The first one is based on a polarization transfer from the NV electron spin to the 13C nucleus, which is mediated by the anisotropic component of the hyperfine interaction. The second one relies on coherent population trapping (CPT) within a Λ-type energy-level configuration in the microwave domain, which enables to initialize the 13C nuclear spin in any quantum state superposition on the Bloch sphere. This CPT protocol is performed in an unusual regime for which relaxation from the excited level of the Λ-scheme is externally triggered by optical pumping and separated in time from coherent microwave excitations. For these two polarization techniques, we investigate the impact of optical illumination on the nuclear spin polarization efficiency. This work adds new methods to the quantum toolbox used for coherent control of individual nuclear spins in diamond, which might find applications in quantum metrology.

Ref HAL: hal-03837709_v1
Ref Arxiv: 2210.05485
Ref INSPIRE: 2164234
Ref. & Cit.: NASA ADS
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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-02493073_v1
DOI: 10.1063/1.5140030
WoS: 000519594400001
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Nitrogen-vacancy centers in diamonds possess an electronic spin resonance that strongly depends on temperature, which makes them efficient temperature sensors with sensitivity down to a few mK/√Hz. However, the high thermal conductivity of the host diamond may strongly damp any temperature variations, leading to invasive measurements when probing local temperature distributions. In the view of determining possible and optimal con gurations for diamond-based wide- eld thermal imaging, here, we investigate both experimentally and numeri- cally the effect of the presence of diamonds on microscale temperature distributions. Three geometrical con gurations are studied: a bulk diamond substrate, a thin diamond layer bonded on quartz, and diamond nanoparticles dispersed on quartz. We show that the use of bulk diamond substrates for thermal imaging is highly invasive in the sense that it prevents any substantial temperature increase. Conversely, thin diamond layers partly solve this issue and could provide a possible alternative for microscale thermal imaging. Dispersions of diamond nanoparticles throughout the sample appear as the most relevant approach as they do not affect the temperature distribution, although NV centers in nanodiamonds yield lower temperature sensitivities than bulk diamonds.

Ref HAL: hal-02379667_v1
DOI: 10.1103/PhysRevLett.123.063601
WoS: WOS:000479005200002
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10 Citations
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We report on the realization and verification of quantum entanglement between a nitrogen-vacancy electron spin qubit and a telecom-band photonic qubit. First we generate entanglement between the spin qubit and a 637 nm photonic time-bin qubit, followed by photonic quantum frequency conversion that transfers the entanglement to a 1588 nm photon. We characterize the resulting state by correlation measurements in different bases and find a lower bound to the Bell state fidelity of ≥ 0.77± 0.03. This result presents an important step towards extending quantum networks via optical fiber infrastructure.

Ref HAL: hal-02302063_v1
DOI: 10.1016/j.diamond.2019.04.022
WoS: WOS:000474324600011
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3 Citations
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Control of the crystalline orientation of nitrogen-vacancy (NV) defects in diamond is here demonstrated by tuning the temperature of chemical vapor deposition (CVD) growth on a (113)-oriented diamond substrate. We show that preferential alignment of NV defects along the [111] axis is improved when the CVD growth temperature is decreased, leading to $79\%$ preferential orientation at 800°C, as compared to only 47.5% at 1000°C. This effect is then combined with temperature-dependent incorporation of NV defects during the CVD growth to obtain preferential alignment over dense ensembles of NV defects spatially localized in thin diamond layers. These results demonstrate that growth temperature can be exploited as an additional degree of freedom to engineer optimized diamond samples for quantum sensing applications.

Ref HAL: hal-02289672_v1
DOI: 10.1103/PhysRevMaterials.3.094001
WoS: 000483945800001
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34 Citations
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We study shallow and deep levels in carbon-doped hexagonal boron nitride crystals precipitated from a molten metal solution in a high-temperature furnace. Reflectance and photoluminescence under deep ultraviolet excitation are complemented by spatially resolved experiments by means of a scanning confocal micro-photoluminescence setup operating in the ultraviolet. Isotopically controlled carbon doping does not induce any energy shift of the well-known deep-level emission at 4.1 eV. Our detailed characterization in a series of carbon-doped crystals reveals that the incorporation of carbon during the growth process results in a distinct class of shallow and deep levels in hexagonal boron nitride, calling into question the exact role of carbon in the growth of hexagonal boron nitride and its direct or indirect influence on the formation of the crystal defects.

Ref HAL: hal-02003644_v1
Ref Arxiv: 1801.03304
DOI: 10.1103/PhysRevApplied.9.064031
WoS: WOS:000435552500005
Ref. & Cit.: NASA ADS
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34 Citations
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We report on the conversion to telecom wavelength of single photons emitted by a nitrogen-vacancy (NV) defect in diamond. By means of difference frequency generation, we convert spin-selective photons at 637 nm, associated with the coherent NV zero-phonon-line, to the target wavelength of 1588 nm in the L-telecom band. The successful conversion is evidenced by time-resolved detection revealing a telecom photon lifetime identical to that of the original 637 nm photon. Furthermore, we show by second-order correlation measurements that the single-photon statistics are preserved. The overall efficiency of this one-step conversion reaches 17\% in our current setup, along with a signal-to-noise ratio of $\approx$7 despite the low probability $(< 10^{-3})$ of an incident 637 nm photon. This result shows the potential for efficient telecom photon - NV center interfaces and marks an important step towards future long-range entanglement-based quantum networks.

Commentaires: . Réf Journal: Phys. Rev. Applied 9, 064031 (2018)