Stabilisation of an optical transition energy via nuclear Zeno dynamics in quantum dot-cavity systems

We investigate the effect of nuclear spins on the phase shift and polarisation rotation of photons scattered off a quantum dot-cavity system. We show that as the phase shift depends strongly on the resonance energy of an electronic transition in the quantum dot, it can provide a sensitive probe of the quantum state of nuclear spins that broaden this transition energy. By including the electron-nuclear spin coupling at a Hamiltonian level within an extended input-output formalism, we show how a photon scattering event acts as a nuclear spin measurement, which when rapidly applied leads to an inhibition of the nuclear spin dynamics via the quantum Zeno effect, and a corresponding stabilisation of the optical resonance. We show how such an effect manifests in the intensity autocorrelation $g^{(2)}(\tau)$ of scattered photons, whose long-time bunching behaviour changes from quadratic decay for low photon scattering rates (weak laser intensities), to ever slower exponential decay for increasing laser intensities as optical measurements impede the nuclear spin evolution.Comment: 8 pages, 3 figure

Wavelet Neural Network Methodology for Ground Resistance Forecasting

Motivated by the need of engineers for a flexible and reliable tool for estimating and predicting grounding systems behavior, this study developed a model that accurately describes and forecasts the dynamics of ground resistance variation. It is well-known that grounding systems are a key of high importance for the safe operation of electrical facilities, substations, transmission lines and, generally, electric power systems. Yet, in most cases, during the design stage, electrical engineers and researchers have limited information regarding the terrain’s soil resistivity variation. Moreover, the periodic measurement of ground resistance is hindered very often by the residence and building infrastructure. The model, developed in the present study, consists of a nonlinear, nonparametric Wavelet Neural Network (WNN), trained in field measurements of soil resistivity and rainfall height, observed the past four years. The proposed framework is tested in five different grounding systems with different ground enhancing compounds, so that can be used for the evaluation of the behavior of several ground enhancing compounds, frequently used in grounding practice. The research results indicate that the WNN can constitute an accurate model for ground resistance forecasting and can be a useful tool in the disposal of electrical engineers. Therefore, this paper introduces the wavelet analysis in the field of ground resistance evaluation and endeavors to take advantage of the benefits of computational intelligence

Quantum modulation of a coherent state wavepacket with a single electron spin

The interaction of quantum objects lies at the heart of fundamental quantum physics and is key to a wide range of quantum information technologies. Photon-quantum-emitter interactions are among the most widely studied. Two-qubit interactions are generally simplified into two quantum objects in static well-defined states . In this work we explore a fundamentally new dynamic type of spin-photon interaction. We demonstrate modulation of a coherent narrowband wavepacket with another truly quantum object, a quantum dot with ground state spin degree of freedom. What results is a quantum modulation of the wavepacket phase (either 0 or {\pi} but no values in between), a new quantum state of light that cannot be described classically.Comment: Supplementary Information available on reques

Charged quantum dot micropillar system for deterministic light-matter interactions

This work was funded by the Future Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, FET-Open, FP7-284743 [project Spin Photon Angular Momentum Transfer for Quantum Enabled Technologies (SPANGL4Q)] and the German Ministry of Education and research (BMBF) and Engineering and Physical Sciences Research Council (EPSRC) [project Solid State Quantum Networks (SSQN)]. J.G.R. is sponsored by the EPSRC fellowship EP/M024458/1.Quantum dots (QDs) are semiconductor nanostructures in which a three-dimensional potential trap produces an electronic quantum confinement, thus mimicking the behavior of single atomic dipole-like transitions. However, unlike atoms, QDs can be incorporated into solid-state photonic devices such as cavities or waveguides that enhance the light-matter interaction. A near unit efficiency light-matter interaction is essential for deterministic, scalable quantum-information (QI) devices. In this limit, a single photon input into the device will undergo a large rotation of the polarization of the light field due to the strong interaction with the QD. In this paper we measure a macroscopic (∼6∘) phase shift of light as a result of the interaction with a negatively charged QD coupled to a low-quality-factor (Q∼290) pillar microcavity. This unexpectedly large rotation angle demonstrates that this simple low-Q-factor design would enable near-deterministic light-matter interactions.Publisher PDFPeer reviewe

Optically detected spin-orbit torque ferromagnetic resonance in an in-plane magnetized ellipse (article)

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this recordThe dataset associated with this article is available in ORE at: https://doi.org/10.24378/exe.3343Time-resolved scanning Kerr microscopy has been used to perform optically-detected, phaseresolved spin-orbit torque ferromagnetic resonance (SOT-FMR) measurements on a microscale CoFeB ellipse at the centre of a Pt Hall cross subject to RF and DC current. Time-resolved polar Kerr images revealed localized dynamics with large amplitude at the center, and weaker amplitude at the edges. Therefore, field swept SOT-FMR spectra were acquired from the so-called center mode to probe the SOTs active at the center of the ellipse, thus minimising non-uniform edge contributions. When the magnetic field was applied at 30° from the hard axis of the ellipse and a DC current applied, a marked asymmetry was observed in the amplitude and linewidth of the FMR peaks as the applied field was reversed. Both absorptive and dispersive parts of the spectra were in good agreement with a macrospin calculation. The damping parameter (α) and the Slonczewski torque parameter (ST) were determined to be 0.025 and (6.75±0.75)×10-7 Oe A-1 cm2 respectively. The hard axis SOT-FMR linewidth was found to be almost independent of the DC current value, suggesting that the SOT has minimal influence in the hard axis configuration and also that thermal effects were insignificant. This study paves the way to spatially-resolved measurements of SOT probed using localized modes of microscale devices that go beyond the spatially averaged capability of electrical measurement techniques.Engineering and Physical Sciences Research Council (EPSRC

Photonic transistor and router using a single quantum-dotconfined spin in a single-sided optical microcavity

The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security guaranteed by the laws of quantum mechanics. Photons would be used for processing, routing and com-munication of data, and photonic transistor using a weak light to control a strong light is the core component as an optical analogue to the electronic transistor that forms the basis of modern electronics. In sharp contrast to previous all-optical tran-sistors which are all based on optical nonlinearities, here I introduce a novel design for a high-gain and high-speed (up to terahertz) photonic transistor and its counterpart in the quantum limit, i.e., single-photon transistor based on a linear optical effect: giant Faraday rotation induced by a single electronic spin in a single-sided optical microcavity. A single-photon or classical optical pulse as the gate sets the spin state via projective measurement and controls the polarization of a strong light to open/block the photonic channel. Due to the duality as quantum gate for quantum information processing and transistor for optical information processing, this versatile spin-cavity quantum transistor provides a solid-state platform ideal for all-optical networks and quantum networks

Effect of surrounding environment on grounding systems

191 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) "Παραγωγή και Διαχίριση Ενέργειας"Σκοπός της παρούσας μεταπτυχιακής εργασίας είναι η μελέτη της συμπεριφοράς διαφόρων βελτιωτικών υλικών, τα οποία χρησιμοποιούνται ευρύτατα στα συστήματα γειώσεων για την ελάττωση της αντίστασης γείωσης, σε συνάρτηση με το χρόνο, τις περιβαλλοντικές συνθήκες, τη θερμοκρασία και την υγρασία του εδάφους. Η χαμηλή τιμή της αντίστασης γείωσης διασφαλίζει την απρόσκοπτη ροή όλου του ρεύματος σφάλματος, μέσω του ηλεκτροδίου γείωσης, προς τη γη και έχει ως αποτέλεσμα την ασφάλεια του προσωπικού και του ηλεκτρολογικού εξοπλισμού της εγκατάστασης.It is an aim of this post-graduate thesis tο study the behavior of ground enhancing compounds, which are widely used in grounding systems, aiming to decrease grounding resistance value. All this in relation to time, environmental conditions, soil temperature and humidity. Low grounding resistance value ensures that the fault current, mainly through the grounding electrode, flows smoothly into the earth. This results in the safety of both installation personnel and power equipment involved.Βασίλειος Π. Ανδροβιτσανέα

Exploitation of a controlled climatic conditions chamber-Effect of climatic conditions on the air dielectric strength under impulse test

158 σ.Η παρούσα διπλωματική εργασία, ακολουθώντας τις επιταγές της εφαρμοσμένης τεχνολογίας στον τομέα των Υψηλών Τάσεων, σκοπό έχει να μελετήσει το φαινόμενο της ηλεκτρικής διάσπασης των διακένων αέρα υπό κρουστικές υψηλές τάσεις μικρής διάρκειας (1,2/50), οι οποίες προσομοιώνουν εργαστηριακά τις εξωτερικές υπερτάσεις από ηλεκτρικά ατμοσφαιρικά φαινόμενα (κεραυνοί). Λόγω της μεγάλης σημασίας που έχει αυτό το φαινόμενο, για την προστασία των τεχνικών εγκαταστάσεων και των συστημάτων ηλεκτρικής ενέργειας από τα κεραυνικά πλήγματα, από τα οδεύοντα κύματα υπερτάσεων που δημιουργούνται στις γραμμές μεταφοράς και στις τεχνικές εγκαταστάσεις και γενικότερα από πάσης φύσεως υπερτάσεις που μπορούν να προκαλέσουν διάσπαση του μονωτικού του αέρα, γίνεται προσπάθεια μελέτης όχι μόνο των μηχανισμών της διάσπασης αλλά και των παραγόντων που επιδρούν σε αυτούς τους μηχανισμούς, όπως π.χ. η θερμοκρασία, η υγρασία, το μήκος του διακένου, η τιμή της τάσης κ.α.The present diploma thesis, following the requirements of the applied technology in the High Voltage devision, aims to investigate the electrical breakdown of air gaps under impulse high voltage (1.2/50 μs), which simulates in laboratory tests the surge voltages caused by atmospheric phenomena, e.g. lightning. Due to the great importance of this phenomenon for the lightning protection of electrical installations, power systems and transmission lines, an attempt is carried out for the study not only of the breakdown mechanisms but also of the factors that effect on these mechanisms, such as temperature, air humidity, air gap length, voltage value, etc.Βασίλειος Π. Ανδροβιτσανέα