11 research outputs found
Optical properties of an ensemble of G-centers in silicon
We addressed the carrier dynamics in so-called G-centers in silicon
(consisting of substitutional-interstitial carbon pairs interacting with
interstitial silicons) obtained via ion implantation into a
silicon-on-insulator wafer. For this point defect in silicon emitting in the
telecommunication wavelength range, we unravel the recombination dynamics by
time-resolved photoluminescence spectroscopy. More specifically, we performed
detailed photoluminescence experiments as a function of excitation energy,
incident power, irradiation fluence and temperature in order to study the
impact of radiative and non-radiative recombination channels on the spectrum,
yield and lifetime of G-centers. The sharp line emitting at 969 meV (1280
nm) and the broad asymmetric sideband developing at lower energy share the same
recombination dynamics as shown by time-resolved experiments performed
selectively on each spectral component. This feature accounts for the common
origin of the two emission bands which are unambiguously attributed to the
zero-phonon line and to the corresponding phonon sideband. In the framework of
the Huang-Rhys theory with non-perturbative calculations, we reach an
estimation of 1.60.1 \angstrom for the spatial extension of the
electronic wave function in the G-center. The radiative recombination time
measured at low temperature lies in the 6 ns-range. The estimation of both
radiative and non-radiative recombination rates as a function of temperature
further demonstrate a constant radiative lifetime. Finally, although G-centers
are shallow levels in silicon, we find a value of the Debye-Waller factor
comparable to deep levels in wide-bandgap materials. Our results point out the
potential of G-centers as a solid-state light source to be integrated into
opto-electronic devices within a common silicon platform
Single artificial atoms in silicon emitting at telecom wavelengths
Given its unrivaled potential of integration and scalability, silicon is
likely to become a key platform for large-scale quantum technologies.
Individual electron-encoded artificial atoms either formed by impurities or
quantum dots have emerged as a promising solution for silicon-based integrated
quantum circuits. However, single qubits featuring an optical interface needed
for large-distance exchange of information have not yet been isolated in such a
prevailing semiconductor. Here we show the isolation of single optically-active
point defects in a commercial silicon-on-insulator wafer implanted with carbon
atoms. These artificial atoms exhibit a bright, linearly polarized
single-photon emission at telecom wavelengths suitable for long-distance
propagation in optical fibers. Our results demonstrate that despite its small
bandgap (~ 1.1 eV) a priori unfavorable towards such observation, silicon can
accommodate point defects optically isolable at single scale, like in
wide-bandgap semiconductors. This work opens numerous perspectives for
silicon-based quantum technologies, from integrated quantum photonics to
quantum communications and metrology
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Exploration of Defect Dynamics and Color Center Qubit Synthesis with Pulsed Ion Beams
Short-pulse ion beams have been developed in recent years and now enable applications in materials science. A tunable flux of selected ions delivered in pulses of a few nanoseconds can affect the balance of defect formation and dynamic annealing in materials. We report results from color center formation in silicon with pulses of 900 keV protons. G-centers in silicon are near-infrared photon emitters with emerging applications as single-photon sources and for spin-photon qubit integration. G-centers consist of a pair of substitutional carbon atoms and one silicon interstitial atom and are often formed by carbon ion implantation and thermal annealing. Here, we report on G-center formation with proton pulses in silicon samples that already contained carbon, without carbon ion implantation or thermal annealing. The number of G-centers formed per proton increased when we increased the pulse intensity from 6.9 Ă 109 to 7.9 Ă 1010 protons/cm2/pulse, demonstrating a flux effect on G-center formation efficiency. We observe a G-center ensemble linewidth of 0.1 nm (full width half maximum), narrower than previously reported. Pulsed ion beams can extend the parameter range available for fundamental studies of radiation-induced defects and the formation of color centers for spin-photon qubit applications
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Effect of localization on photoluminescence and zero-field splitting of silicon color centers
The study of defect centers in silicon has been recently reinvigorated by their potential applications in optical quantum information processing. A number of silicon defect centers emit single photons in the telecommunication O-band, making them promising building blocks for quantum networks between computing nodes. The two-carbon G-center, self-interstitial W-center, and spin-1/2 T-center are the most intensively studied silicon defect centers, yet despite this, there is no consensus on the precise configurations of defect atoms in these centers, and their electronic structures remain ambiguous. Here we employ ab initio density functional theory to characterize these defect centers, providing insight into the relaxed structures, band structures, and photoluminescence spectra, which are compared to experimental results. Motivation is provided for how these properties are intimately related to the localization of electronic states in the defect centers. In particular, we present the calculation of the zero-field splitting for the excited triplet state of the G-center defect as the structure is linearly interpolated from the A-configuration to the B-configuration, showing a sudden increase in the magnitude of the Dzz component of the zero-field-splitting tensor. By performing projections onto the local orbital states of the defect, we analyze this transition in terms of the symmetry and bonding character of the G-center defect, which sheds light on its potential application as a spin-photon interface
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All-silicon quantum light source by embedding an atomic emissive center in a nanophotonic cavity
Silicon is the most scalable optoelectronic material but has suffered from its inability to generate directly and efficiently classical or quantum light on-chip. Scaling and integration are the most fundamental challenges facing quantum science and technology. We report an all-silicon quantum light source based on a single atomic emissive center embedded in a silicon-based nanophotonic cavity. We observe a more than 30-fold enhancement of luminescence, a near-unity atom-cavity coupling efficiency, and an 8-fold acceleration of the emission from the all-silicon quantum emissive center. Our work opens immediate avenues for large-scale integrated cavity quantum electrodynamics and quantum light-matter interfaces with applications in quantum communication and networking, sensing, imaging, and computing
Single artificial atoms in silicon emitting at telecom wavelengths
Given its potential for integration and scalability, silicon is likely to be a key platform for large-scale quantum technologies. Individual electron-encoded artificial atoms, formed by either impurities or quantum dots, have emerged as a promising solution for silicon-based integrated quantum circuits. However, single qubits featuring an optical interface, which is needed for long-distance exchange of information, have not yet been isolated in silicon. Here we report the isolation of single optically active point defects in a commercial silicon-on-insulator wafer implanted with carbon atoms. These artificial atoms exhibit a bright, linearly polarized single-photon emission with a quantum efficiency of the order of unity. This single-photon emission occurs at telecom wavelengths suitable for long-distance propagation in optical fibres. Our results show that silicon can accommodate single isolated optical point defects like in wide-bandgap semiconductors, despite a small bandgap (1.1âeV) that is unfavourable for such observations
Effect of general anaesthesia on functional outcome in patients with anterior circulation ischaemic stroke having endovascular thrombectomy versus standard care: a meta-analysis of individual patient data
Background:
General anaesthesia (GA) during endovascular thrombectomy has been associated with worse patient outcomes in observational studies compared with patients treated without GA. We assessed functional outcome in ischaemic stroke patients with large vessel anterior circulation occlusion undergoing endovascular thrombectomy under GA, versus thrombectomy not under GA (with or without sedation) versus standard care (ie, no thrombectomy), stratified by the use of GA versus standard care.
Methods:
For this meta-analysis, patient-level data were pooled from all patients included in randomised trials in PuMed published between Jan 1, 2010, and May 31, 2017, that compared endovascular thrombectomy predominantly done with stent retrievers with standard care in anterior circulation ischaemic stroke patients (HERMES Collaboration). The primary outcome was functional outcome assessed by ordinal analysis of the modified Rankin scale (mRS) at 90 days in the GA and non-GA subgroups of patients treated with endovascular therapy versus those patients treated with standard care, adjusted for baseline prognostic variables. To account for between-trial variance we used mixed-effects modelling with a random effect for trials incorporated in all models. Bias was assessed using the Cochrane method. The meta-analysis was prospectively designed, but not registered.
Findings:
Seven trials were identified by our search; of 1764 patients included in these trials, 871 were allocated to endovascular thrombectomy and 893 were assigned standard care. After exclusion of 74 patients (72 did not undergo the procedure and two had missing data on anaesthetic strategy), 236 (30%) of 797 patients who had endovascular procedures were treated under GA. At baseline, patients receiving GA were younger and had a shorter delay between stroke onset and randomisation but they had similar pre-treatment clinical severity compared with patients who did not have GA. Endovascular thrombectomy improved functional outcome at 3 months both in patients who had GA (adjusted common odds ratio (cOR) 1·52, 95% CI 1·09â2·11, p=0·014) and in those who did not have GA (adjusted cOR 2·33, 95% CI 1·75â3·10, p<0·0001) versus standard care. However, outcomes were significantly better for patients who did not receive GA versus those who received GA (covariate-adjusted cOR 1·53, 95% CI 1·14â2·04, p=0·0044). The risk of bias and variability between studies was assessed to be low.
Interpretation:
Worse outcomes after endovascular thrombectomy were associated with GA, after adjustment for baseline prognostic variables. These data support avoidance of GA whenever possible. The procedure did, however, remain effective versus standard care in patients treated under GA, indicating that treatment should not be withheld in those who require anaesthesia for medical reasons