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Stefania Castelletto

Publications and source records attributed to Stefania Castelletto.

18 recordsLinked to original sources

Room temperature Purcell enhanced single erbium ions in silicon-carbide-on-insulator microring resonators

Spin-carrying single-photon emitters operating in the telecommunication C-band (1530-1565nm) are prime candidates for integrated spin-photon interfaces, offering seamless compatibility with existing fiber-optic infrastructure, an essential component for future quantum networks. In this context, erbium-dopants ($\text{Er}^{3+}$) are particularly compelling due to their exceptional emitter properties, including small spectral diffusion and long spin coherence times. However, their low C-band photon-emission rate and operation at cryogenic temperatures has limited the realization of this technology. In this work, we demonstrate fully integrated single-photon emission from an ion implanted $\text{Er}^{3+}$-embedded into a 4H-silicon-carbide-on-insulator (4H-SiCOI) microring resonator operating at room temperature. By optimizing the mode overlap between the resonator and the $\text{Er}^{3+}$-defect, we achieved a $\sim$70$\times$ Purcell enhancement and recorded small spectral diffusion of $\sim$54 MHz. We further characterize the $\text{Er}^{3+}$ single photon emission via photon correlation g$^{(2)}$-histograms and investigate its performance under varying magnetic-field, demonstrating Zeeman splitting on single emitters.

physics.optics

Fano-Like Resonances in Coupled Sagnac Interferometers Formed by a Self-Coupled Waveguide

We demonstrate Fano-like resonances in silicon-on-insulator (SOI) nanowire-based coupled Sagnac interferometers (SIs) formed by a self-coupled waveguide. By adjusting the reflectivity of the two SIs and coupling strength between them, we tailor coherent mode interference to achieve high-performance optical analogues of Fano resonance. The device is theoretically analyzed and experimentally fabricated on a SOI platform. Theoretical analysis predicts periodic Fano-like resonances with a high extinction ratio and a steep slope rate, arising from strong coherent optical mode interference within a compact resonator comprising two SIs and a connected feedback waveguide. Experimental results align with the theoretical model, validating the expected resonance behavior and confirming the effectiveness of the design. These findings underscore the potential of compact coupled SIs for generating Fano-like resonances, enabling broader applications in integrated photonics.

physics.optics

Narrow magneto-optical transitions in Erbium implanted silicon carbide-on-insulator

Solid state spin photon interfaces operating in the near telecom and telecom bands are a key resource for long distance quantum communication and scalable quantum networks. However, their optical transitions often suffer from spectral diffusion that hampers the generation of coherent spin photon entanglement. Here we demonstrate narrow magneto-optical transitions of erbium dopants implanted into thin film silicon carbide (SiC)-on-insulator, a viable platform for industrially scalable quantum networks. Using high-resolution resonant spectroscopy and spectral hole burning at cryogenic temperatures, we reveal sub megahertz homogeneous linewidths and identify two lattice sites that best stabilise the emitters. We further characterise their optical lifetimes and magneto-optical response, establishing erbium doped SiC-on-insulator as a robust and scalable platform for on-chip quantum networks.

cond-mat.mtrl-sci

Coupling 4H-Silicon Carbide spins to a microwave resonator at milli-Kelvin temperature

Coupling microwave cavity modes with spin qubit transitions is crucial for enabling efficient qubit readout and control, long-distance qubit coupling, quantum memory implementation, and entanglement generation. We experimentally observe the coupling of different spin qubit transitions in Silicon Carbide (SiC) material to a 3D microwave (MW resonator mode around 12.6~GHz at a temperature of 10~mK. Tuning the spin resonances across the cavity resonance via magnetic-field sweeps, we perform MW cavity transmission measurements. We observe spin transitions of different spin defects that are detuned from each other by around 60-70~MHz. By optically exciting the SiC sample placed in the MW cavity with an 810~nm laser, we observe the coupling of an additional spin resonance to the MW cavity, also detuned by around 60-70 MHz from the centre resonance. We perform complementary confocal optical spectroscopy as a function of temperature from 4~K to 200~K. Combining the confocal spectroscopy results and a detailed analysis of the MW-resonator-based experiments, we attribute the spin resonances to three different paramagnetic defects: positively-charged carbon antisite vacancy pair (CAV$^+$), and the negatively-charged silicon vacancy spins located at two different lattice sites, namely V$_1$ and V$_2$ spins. The V$_1$ and V$_2$ lines in SiC are interesting qubit transitions since they are known to be robust to decoherence. Additionally, the CAV$^+$-transition is known to be a bright single-photon source. Consequently, the demonstration of the joint coupling of these spin qubits to a MW cavity mode could lead to interesting new modalities: The microwave cavity could act as an information bus and mediate long-range coupling between the spins, with potential applications in quantum computing and quantum communication, which is an attractive proposition in a CMOS-compatible material such as SiC.

quant-ph

Integration of $\text{Er}^{3+}$-emitters in silicon-on-insulator nanodisks metasurface

Erbium ($\text{Er}^{3+}$) emitters are relevant for optical applications due to their narrow emission line directly in the telecom C-band due to the ${}^\text{4}\text{I}_{\text{13/2}}$ $\rightarrow$ ${}^\text{4}\text{I}_{\text{15/2}}$ transition at 1.54 $\mu$m. Additionally they are promising candidates for future quantum technologies when embedded in thin-film silicon-on-insulator (SOI) to achieve fabrication scalability and CMOS compatibility. In this paper we integrate $\text{Er}^{3+}$ emitters in SOI metasurfaces made of closely spaced array of nanodisks, to study their spontaneous emission via room and cryogenic temperature confocal microscopy, off-resonance and in-resonance photoluminescence excitation at room temperature and time resolved spectroscopy. This work demonstrates the possibility to adopt CMOS-compatible and fabrication scalable metasurfaces for controlling and improving the collection efficiency of the spontaneous emission from the $\text{Er}^{3+}$ transition in SOI and could be adopted in similar technologically advanced materials.

physics.optics

Photo-luminescence properties of ion implanted Er3+-defects in 4H-SiCOI towards integrated quantum photonics

Colour centres hosted in solid-state materials such as silicon carbide and diamond are promising candidates for integration into chip-scale quantum systems. Specifically, the incorporation of these colour centres within photonic integrated circuits may enable precise control over their inherent photo-physical properties through strong light-matter interaction. Here, we investigate ion-implanted erbium ($\text{Er}^{3+}$) defects embedded in thin-film 4H-silicon-carbide-on-insulator (4H-SiCOI). Optimized implantation conditions and thermal annealing processes designed to enhance the emission characteristics of the $\text{Er}^{3+}$-defect are reported. By examining key properties such as photoluminescence intensity, optical lifetime, and polarization, we present an analysis of ensemble $\text{Er}^{3+}$-defects within 4H-SiCOI, providing insights into their potential for future quantum applications.

physics.optics

Laser writing and spin control of near infrared emitters in silicon carbide

Near infrared emission in silicon carbide is relevant for quantum technology specifically single photon emission and spin qubits for integrated quantum photonics, quantum communication and quantum sensing. In this paper we study the fluorescence emission of direct femtosecond laser written array of color centres in silicon carbide followed by thermal annealing. We show that in high energy laser writing pulses regions a near telecom O-band ensemble fluorescence emission is observed after thermal annealing and it is tentatively attributed to the nitrogen vacancy centre in silicon carbide. Further in the low energy laser irradiation spots after annealing, we fabricated few divacancy, PL5 and PL6 types and demonstrate their optical spin read-out, and coherent spin manipulation (Rabi and Ramsey oscillations and spin echo). We show that direct laser writing and thermal annealing can yield bright near telecom emission and preserve the spin coherence time of divacancy at room temperature.

cond-mat.mtrl-sci

Silicon Carbide Metasurfaces for Controlling the Spontaneous Emission of Embedded Color Centers

While electric and magnetic dipolar resonances in SiC have been studied in the far-infrared, they have not been studied in the near infrared. Here we show for the first time that electromagnetic Mie-scattering moments within SiC metasurfaces can control the spontaneous emission process of point defects in the near infrared. Using SiC nanopillars based metasurfaces, we theoretically demonstrate a control over the spontaneous emission rate of embedded color-centers by using the coherent superposition of the electric dipolar and magnetic quadrupolar electromagnetic Mie-scattering moments of the structure. More than an order of magnitude emission/decay rate enhancement is obtained with the maximum enhancement close to 30. We also demonstrate that the relative phase of the Mie-scattering moments helps in controlling the emission directionality. SiC metasurfaces in the spectral range of color centres, from the visible to the near infrared, can be used to control the confinement and directionality of their spontaneous emission, increasing the opportunities to study light-matter interaction and to advance quantum photonic and quantum sensing device integration.

physics.optics

Spin Relaxation in Quasi-1D GaAs Mesowires: Control via Electric Field and Aspect Ratio

We report on the measurements of spin relaxation in GaAs quasi-one-dimensional mesowires, relying on spin noise spectroscopy, thus adding to the existing body of spin relaxation studies in bulk, two-dimensional and zero dimensional systems. In addition to temperature and magnetic field dependence, we modify the spin relaxation time via applied electric field and aspect ratio of the mesowires, suggesting that scalable spintronics devices with controllable spin relaxation are achievable. Overall, we observed higher spin-relaxation time in mesowires compared to bulk with a spin noise exhibiting Dyakonov-Perel scattering and other scattering behavior. Spectral spin noise data are interpreted in part via Glazov-Sherman model, where both, diffusive and ballistic spin relaxation are accounted for.

cond-mat.mes-hall

Strong Coupling Between P1 Diamond Impurity Centres and 3D Lumped Photonic Microwave Cavity

We report strong coupling between an ensemble of N impurity (P1) centres in diamond and microwave photons using a unique double post re-entrant cavity. The cavity is designed so that the magnetic component of the cavity field is spatially separated from the electric component and focused into the small volume in which the diamond sample is mounted. The novelty of the structure simultaneously allows high magnetic filling factor (38.4\%) and low frequencies necessary to interact, at low magnetic field, with transitions in diamond such as those in NV$^{-}$ and P1 centres. Coupling strength (or normal-mode splitting) of 51.42 MHz, was achieved with P1 centres at 6.18 GHz and 220 mT in a centimetre-scale cavity, with a corresponding cooperativity factor of 4.7. This technique offers an alternative way, with some significant advantages, to couple 3D cavities to transitions in diamond and achieve the strong coupling necessary for applications to quantum information processing.

cond-mat.mes-hall

Quantum-confined single photon emission at room temperature from Silicon carbide tetrapods

Controlled engineering of isolated solid state quantum systems is one of the most prominent goals in modern nanotechnology. In this letter we demonstrate a previously unknown quantum system namely silicon carbide tetrapods. The tetrapods have a cubic polytype core (3C) and hexagonal polytype legs (4H) a geometry that creates a spontaneous polarization within a single tetrapod. Modeling of the tetrapod structures predict that a bound exciton should exist at the 3C 4H interface. The simulations are confirmed by the observation of fully polarized and narrowband single photon emission from the tetrapods at room temperature. The single photon emission provides important insights towards understanding the quantum confinement effects in non-spherical nanostructures. Our results pave the way to a new class of crystal phase nanomaterials that exhibit single photon emission at room temperature and therefore are suitable for sensing, quantum information and nanophotonics.

cond-mat.mtrl-sci

Single photon emission from ZnO nanoparticles

Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work we study single photon emission from defect centers in 20 nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640 nm with polarized excitation and emission. The studied emitters showed continuous blinking, however, bleaching can be suppressed using a polymethyl methacrylate (PMMA) coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO.

cond-mat.mtrl-sci

Nanodiamonds with silicon vacancy defects for non-toxic photostable fluorescent labeling of neural precursor cells

Nanodiamonds (NDs) containing silicon vacancy (SiV) defects were evaluated as a potential biomarker for the labeling and fluorescent imaging of neural precursor cells (NPCs). SiV-containing NDs were synthesized using chemical vapor deposition and silicon ion implantation. Spectrally, SiV-containing NDs exhibited extremely stable fluorescence and narrow bandwidth emission with an excellent signal to noise ratio exceeding that of NDs containing nitrogen-vacancy (NV) centers. NPCs labeled with NDs exhibited normal cell viability and proliferative properties consistent with biocompatibility. We conclude that SiVcontaining NDs are a promising biomedical research tool for cellular labeling and optical imaging in stem cell research.

physics.bio-ph

Tracking Emission Rate Dynamics of NV Centers in Nanodiamonds

Spontaneous emission from crystal centers is influenced by both the photonic local density of states and non-radiative processes. Here we monitor the spontaneous emission of single nitrogen vacancy (NV) centers as their host diamond is reduced in size from a large monolithic crystal to a nanocrystal by successive cycles of oxidation. The size reduction induces a quenching of the NV radiative emission. New non-radiative channels lead to a decrease of the fluorescence intensity and the excited state lifetime. In one case we observe the onset of blinking which may provide a route to understand these additional non-radiative decay channels.

quant-ph

Phonon-induced dephasing of chromium colour centres in diamond

We report on the coherence properties of single photons from chromium-based colour centres in diamond. We use field-correlation and spectral lineshape measurements to reveal the interplay between slow spectral wandering and fast dephasing mechanisms as a function of temperature. We show that the zero-phonon transition frequency and its linewidth follow a power-law dependence on temperature indicating that the dominant fast dephasing mechanisms for these centres are direct electron-phonon coupling and phonon-modulated Coulomb coupling to nearby impurities. Further, the observed reduction in the quantum yield for photon emission as a function of temperature is consistent with the opening of additional nonradiative channels through thermal activation to higher energy states predominantly and indicates a near-unity quantum efficiency at 4 K.

cond-mat.mes-hall

Chromium single photon emitters in diamond fabricated by ion implantation

Controlled fabrication and identification of bright single photon emitters is at the heart of quantum optics and materials science. Here we demonstrate a controlled engineering of a chromium bright single photon source in bulk diamond by ion implantation. The Cr center has fully polarized emission with a ZPL centered at 749 nm, FWHM of 4 nm, an extremely short lifetime of ~1 ns, and a count rate of 500 kcounts/s. By combining the polarization measurements and the vibronic spectra, a model of the center has been proposed consisting of one interstitial chromium atom with a transition dipole along one of the <100> directions.

cond-mat.mtrl-sci

Measurement of Coupling PDC photon sources with single-mode and multimode optical fibers

We investigate the coupling efficiency of parametric downconversion light (PDC) into single and multi-mode optical fibers as a function of the pump beam diameter, crystal length and walk-off. We outline two different theoretical models for the preparation and collection of either single-mode or multi-mode PDC light (defined by, for instance, multi-mode fibers or apertures, corresponding to bucket detection). Moreover, we define the mode-matching collection efficiency, important for realizing a single-photon source based on PDC output into a well-defined single spatial mode. We also define a multimode collection efficiency that is useful for single-photon detector calibration applications.

quant-ph

Coupling Efficiencies in Single Photon On-Demand Sources

Many quantum computation and communication schemes require, or would significantly benefit from, true sources of single photon on-demand (SPOD). Unfortunately, such sources do not exist. It is becoming increasingly clear that coupling photons out of a SPOD source will be a limiting factor in many SPOD implementations. In particular, coupling these source outputs into optical fibers (usually single mode fibers) is often the preferred method for handling this light. We investigate the practical limits to this coupling as relates to parametric downconversion, an important starting point for many SPOD schemes. We also explored whether it is possible to optimize the engineering of the downconversion sources to improve on this coupling. We present our latest results in this area.

quant-ph