Hubert Seigneur

Single-photon Mach–Zehnder interferometer for quantum networks based on the single-photon Faraday effect

Combining the recent progress in semiconductor nanostructures along with the versatility of photonic crystals in confining and manipulating light, quantum networks allow for the prospect of an integrated and low power quantum technology. Within quantum networks, which consist of a system of waveguides and nanocavities with embedded quantum dots, it has been demonstrated in theory that many-qubit states stored in electron spins could be teleported from one quantum dot to another via a single photon using the Single Photon Faraday Effect. However, in addition to being able to transfer quantum information from one location to another, quantum networks need added functionality such as (1) controlling the flow of the quantum information and (2) performing specific operations on qubits that can be easily integrated. In this paper, we show how in principle a single photon Mach-Zehnder interferometer, which uses the concept of the single photon Faraday Effect to manipulate the geometrical phase of a single photon, can be operated both as a switch to control the flow of quantum information inside the quantum network and as various single qubit quantum gates to perform operations on a single photon. Our proposed Mach-Zehnder interferometer can be fully integrated as part of a quantum network on a chip. Given that the X gate, the Z gate, and the XZ gate are essential for the implementation of quantum teleportation, we show explicitly their implementation by means of our proposed single photon Mach-Zehnder interferometer. We also show explicitly the implementation of the Hadamard gate and the single-qubit phase gate, which are needed to complete the universal set of quantum gates for integrated quantum computing in a quantum network.

Dynamics of Entanglement between a Quantum Dot Spin Qubit and a Photon Qubit inside a Semiconductor High-Q Nanocavity

We investigate in this paper the dynamics of entanglement between a QD spin qubit and a single photon qubit inside a quantum network node, as well as its robustness against various decoherence processes. First, the entanglement dynamics is considered without decoherence. In the small detuning regime (Δ=78𝜇eV), there are three different conditions for maximum entanglement, which occur after 71, 93, and 116 picoseconds of interaction time. In the large detuning regime (Δ=1.5meV), there is only one peak for maximum entanglement occurring at 625 picoseconds. Second, the entanglement dynamics is considered with decoherence by including the effects of spin-nucleus and hole-nucleus hyperfine interactions. In the small detuning regime, a decent amount of entanglement (35% entanglement) can only be obtained within 200 picoseconds of interaction. Afterward, all entanglement is lost. In the large detuning regime, a smaller amount of entanglement is realized, namely, 25%. And, it lasts only within the first 300 picoseconds.

Optimization of complete band gaps for photonic crystal slabs through use of symmetry breaking hole shapes

A complete photonic band gap (PBG) in photonic crystal slab (PCS) devices is desirable for various applications, and a realizable device of this kind demands minimal transmittance in-plane as well as out of plane. While in the past much work has considered this problem, none have held transverse confinement as a prime factor. In order to achieve our goal, square and triangular hole shapes are considered. Looking at sharp featured shapes as well as their fabrication realizable rounded counterparts and an even more rudimentary triangular cluster of circles, we look to break the crystalmode symmetries for TM photonic bands and, therefore, open a complete band gap between the 1st and 2nd bands for both TE and TM light. TE/TM gap overlap is optimized for single-slab-mode operation, via the effective index method, for hole size, hole orientation, and slab thickness - all as functions of the lattice constant, a, and operational wavelength, λ. It is found that rounded triangular holes and tri-clustered circular holes of size 0.88a and thickness d/λ = 0.112 show identical photonic behavior that provides an optimized gap overlap of 0.0496 (ωa/2πc = a/λ) with a 12.81% gap figure of merit (Δω/ω0).

Analyses of diamond wire sawn wafers: Effect of various cutting parameters

We have evaluated surface characteristics of diamond wire cut (DWC) wafers sawn under a variety of cutting parameters. These characteristics include surface roughness, spatial frequencies of surface profiles, phase changes, damage depth, and lateral non-uniformities in the surface damage. Various cutting parameters investigated are: wire size, diamond grit size, reciprocating frequency, feed rate, and wire usage. Spatial frequency components of surface topography/roughness are influenced by individual cutting parameters as manifested by distinct peaks in the Fourier transforms of the Dektak profiles. The depth of damage is strongly controlled by diamond grit size and wire usage and to a smaller degree by the wire size.

Correlating wafer surface to DW saw profile and wire wear

The surface of diamond-wire sawn wafers is investigated as a function of different wires. The evolution of the pilgrim waves on the wafer surface is correlated with wire movement. Analysis of wafer surfaces indicated that some wires generate lower surface roughness than others, even using the same sawing recipe.

Mechanical load testing of solar panels — Beyond certification testing

Mechanical load tests are a commonly-performed stress test where pressure is applied to the front and back sides of solar panels. In this paper we review the motivation for load tests and the different ways of performing them. We then discuss emerging durability concerns and ways in which the load tests can be modified and/or enhanced by combining them with other characterization methods. In particular, we present data from a new tool where the loads are applied by using vacuum and air pressure from the rear side of the panels, thus leaving the front side available for EL and IV characterization with the panels in the bent state. Tightly closed cracks in the cells can be temporarily opened by such a test, thus enabling a prediction of panel degradation in the field were these cracks to open up over time. Based on this predictive crack opening test, we introduce the concept of using a quick load test on each panel in the factory as a quality control tool and potentially as a type of burn-in test to initiate cracks that would certainly form early on during a panels field life. We examine the stresses seen by the cells under panel load through Finite Element Modeling and demonstrate the importance of constraining the panel motion during testing as it will be constrained when mounted in the field.

Effect of laser marks and residual stress in wafers on the propensity for performance loss due to cracking in solar cells

In this study, silicon wafers were marked with four different kinds of laser marks. Initial characterization of the wafers was performed to measure various parameters such as minority lifetime, residual stress, wafer thickness, Photoluminescence, and Resonance Ultrasound Imaging. The wafers were consequently processed into solar cells. EL, PL and RUV measurements were also performed on solar cells, in addition to the flash I-V measurements to determine solar cell performance parameters. Cells were laminated into custom modules and the modules were passed through static and dynamic mechanical loading tests according to IEC 61215. A procedure to quantify the performance loss due to cell cracking for each cell was developed and applied for each cell that experienced significant cracking after mechanical loading tests. Following correlations were explored: (i) Propensity of power loss due to cell cracks and residual stress at wafer level (ii) Types of laser marks and their effects on parameters measured in various wafer and cell characterization techniques.

A review of manufacturing metrology for improved reliability of silicon photovoltaic modules

In this work, the use of manufacturing metrology across the supply chain to improve crystalline silicon (c-Si) photovoltaic (PV) module reliability and durability is addressed. Additionally, an overview and summary of a recent extensive literature survey of relevant measurement techniques aimed at reducing or eliminating the probability of field failures is presented. An assessment of potential gaps is also given, wherein the PV community could benefit from new research and demonstration efforts. This review is divided into three primary areas representing different parts of the c-Si PV supply chain: (1) feedstock production, crystallization and wafering; (2) cell manufacturing; and (3) module manufacturing.

Controlled On-Chip Single-Photon Transfer Using Photonic Crystal Coupled-Cavity Waveguides

To the end of realizing a quantum network on-chip, single photons must be guided consistently to their proper destination both on demand and without alteration to the information they carry. Coupled cavity waveguides are anticipated to play a significant role in this regard for two important reasons. First, these structures can easily be included within fully quantum-mechanical models using the phenomenological description of the tight-binding Hamiltonian, which is simply written down in the basis of creation and annihilation operators that move photons from one quasimode to another. This allows for a deeper understanding of the underlying physics and the identification and characterization of features that are truly critical to the behavior of the quantum network using only a few parameters. Second, their unique dispersive properties together with the careful engineering of the dynamic coupling between nearest neighbor cavities provide the necessary control for high-efficiency single-photon on-chip transfer. In this publication, we report transfer efficiencies in the upwards of 93% with respect to a fully quantum-mechanical approach and unprecedented 77% in terms of transferring the energy density contained in a classical quasibound mode from one cavity to another.

Optical Switching Based on the Conditional Faraday Effect With Electron Spins in Quantum Dots

We present the theoretical foundation of a novel concept for optical switching based on the conditional Faraday effect with electron spins in quantum dots (QDs). Calculations for light of wavelengths lambda = 1.3 mum and lambda = 1.55 mum show devices with active regions of a few hundred microns are possible. Case studies for both spherical and nonspherical QDs are considered, with calculations for the nonspherical case showing a 20% reduction in the required device length due to the lifting of the light and heavy hole band degeneracy.