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Search Results: 1 - 10 of 1264 matches for " Stefania Castelletto "
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Coupling Efficiencies in Single Photon On-Demand Sources
Stefania Castelletto,I. P. Degiovanni,Michael Ware,Alan Migdall
Physics , 2003, DOI: 10.1117/12.504773
Abstract: 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.
Tracking Emission Rate Dynamics of NV Centers in Nanodiamonds
Faraz A Inam,Andrew M Edmonds,Michael J Steel,Stefania Castelletto
Physics , 2013, DOI: 10.1063/1.4812711
Abstract: 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.
Single photon emission from ZnO nanoparticles
Sumin Choi,Brett C. Johnson,Stefania Castelletto,Cuong Ton-That,Matthew R. Phillips,Igor Aharonovich
Physics , 2014, DOI: 10.1063/1.4872268
Abstract: 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.
Quantum-confined single photon emission at room temperature from Silicon carbide tetrapods
Stefania Castelletto,Zoltán Bodrog,Andrew P. Magyar,Angus Gentle,Adam Gali,Igor Aharonovich
Physics , 2014, DOI: 10.1039/C4NR02307B
Abstract: 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.
Measurement of Coupling PDC photon sources with single-mode and multimode optical fibers
Stefania Castelletto,Ivo Pietro Degiovanni,Alan Migdall,Valentina Schettini,Michael Ware
Physics , 2004, DOI: 10.1117/12.561831
Abstract: 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.
Phonon-induced dephasing of chromium colour centres in diamond
Tina Muller,Igor Aharonovich,Zhe Wang,Xin Yuan,Stefania Castelletto,Steven Prawer,Mete Atature
Physics , 2012, DOI: 10.1103/PhysRevB.86.195210
Abstract: 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.
Nanodiamonds with silicon vacancy defects for non-toxic photostable fluorescent labeling of neural precursor cells
Tobias D. Merson,Stefania Castelletto,Igor Aharonovich,Alisa Turbic,Trevor J. Kilpatrick,Ann M. Turnley
Quantitative Biology , 2013,
Abstract: 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.
Chromium single photon emitters in diamond fabricated by ion implantation
Igor Aharonovich,Stefania Castelletto,Brett C. Johnson,Jeffrey C. McCallum,David A. Simpson,Andrew D. Greentree,Steven Prawer
Physics , 2010, DOI: 10.1103/PhysRevB.81.121201
Abstract: 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.
Strong Coupling Between P1 Diamond Impurity Centres and 3D Lumped Photonic Microwave Cavity
Daniel L. Creedon,Jean-Michel Le Floch,Maxim Goryachev,Warrick G. Farr,Stefania Castelletto,Michael E. Tobar
Physics , 2014, DOI: 10.1103/PhysRevB.91.140408
Abstract: 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.
An in Vitro Evaluation of Pressure Generated by Programmed Intermittent Epidural Bolus (PIEB) or Continuous Epidural Infusion (CEI)  [PDF]
Silvia Stirparo,Stefania Fortini,Stefania Espa,Antonio Cenedese
Open Journal of Anesthesiology (OJAnes) , 2013, DOI: 10.4236/ojanes.2013.34049
Abstract: PIEB has been reported as being superior to CEI for labor analgesia. The aim of this study was to measure the pressures generated by two commercially available pumps (CADD PIB, Smiths and Gemstar, Hospira) when delivering PIEB or CEI at 2 commonly used rates of infusion (10 or 5 mL). The two pumps were set to deliver fluid at four rates (CEI: 5 or 10 mL/h; PIEB: 5 or 10 mL every h) and connected to a pressure transducer (PCB Piezotronics 1500 connected to a NI USB-6251 Screw Terminal) to determine the pressures applied during each infusion. The peak pressure generated during the PIEB mode was consistently higher when compared to the CEI mode in both pumps. When comparing the two pumps in the PIEB 10 mL every hour mode, the peak pressures were approximately the same, while the pressure pattern differed. For each cycle the pressure generated by Gemstar oscillated from 25 mmHg to 0 mmHg; whereas with the CADD pump the baseline pressure was above 0. The Gemstar pump piston frequency (1.2 Hz) was twice as high as the CADD (0.5 Hz), so the volume delivered per cycle was lower. In the PIEB 5 mL every hour mode the peak pressures followed the same wave patterns. However, unlike the 10 mL mode, the pump piston frequency was approximately the same in both pumps. In both the CEI 5 or 10 mL/h modes, the CADD peak pressure was four times greater than the Gemstar. Both cycled between their respective peak pressures and 0 mmHg. Since the peak pressure of the CADD was approximately the same with PIEB and CEI, we speculated that the most important factor affecting the distribution of the solution in the epidural space was not the peak pressure per se, but the mode of delivery of the bolus.
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