Trapped-ion quantum error-correcting protocols using only global operations

Quantum error-correcting codes are many-body entangled states that are prepared and measured using complex sequences of entangling operations. Each element of such an entangling sequence introduces noise to delicate quantum information during the encoding or reading out of the code. It is important therefore to find efficient entangling protocols to avoid the loss of information. Here we propose an experiment that uses only global entangling operations to encode an arbitrary logical qubit to either the five-qubit repetition code or the five-qubit code, with a six-ion Coulomb crystal architecture in a Penning trap. We show that the use of global operations enables us to prepare and read out these codes using only six and ten global entangling pulses, respectively. The proposed experiment also allows the acquisition of syndrome information during readout. We provide a noise analysis for the presented protocols, estimating that we can achieve a six-fold improvement in coherence time with noise as high as $\sim 1\%$ on each entangling operation.Comment: 7 pages, 4 figures, published version, comments are welcom

Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol and hydroquinone

Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S1 (\u3c0\u3c0*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S1potential surface. In catechol, the overall S1 state lifetime was observed to be 12.1 ps, which is 1\u20132 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S1 state and the close lying S2 (\u3c0\u3c3*) state, which is dissociative along the O\u2013H stretching coordinate. Further evidence of this S1/S2 interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.Peer reviewed: YesNRC publication: Ye

Sources and sinks of carbon dioxide in populous Asia

The recently concluded 21st Conference of the Parties (COP21) under the United Nations Framework Convention on Climate Change (UNFCCC) agreed to limit the increase in global temperature to less than 2oC above pre-industrial levels, with a more aspirational target of 1.5oC. Achieving these policy goals will require extraordinary input from the scientific community to define anthropogenic emission targets that account for natural biosphere sources and sinks of carbon dioxide (CO2), consistent with the climate targets. Asian countries, being densely populated and emerging global economic powers, are key players in defining future emission trajectories. The average fossil emissions from the three regions are estimated to be 2.4, 0.5 and 0.3 PgC yr-1 for East, South and Southeast Asia, respectively, and have increased by 67, 58 and 33% over the period 2003-2012. Here, we estimate land biosphere CO2 fluxes using: 1) simulations of terrestrial ecosystem models driven with global and regional atmospheric and climate observations and 2) atmospheric CO2 inverse models. Based on observations of atmospheric CO2 and inverse models, we show that on average over the period 2003 - 2012, the land biosphere (excluding fossil fuel emissions) in the three Asian regions in our study is either a CO2 sink (0.35 PgC yr-1 in East Asia) or source neutral (South and Southeast Asia). Consistently, our terrestrial ecosystem modeling suggests that the land biosphere of South and Southeast Asia were nearly neutral, but disagrees for East Asia

Quadrilateral-octagon coordinates for almost normal surfaces

Normal and almost normal surfaces are essential tools for algorithmic 3-manifold topology, but to use them requires exponentially slow enumeration algorithms in a high-dimensional vector space. The quadrilateral coordinates of Tollefson alleviate this problem considerably for normal surfaces, by reducing the dimension of this vector space from 7n to 3n (where n is the complexity of the underlying triangulation). Here we develop an analogous theory for octagonal almost normal surfaces, using quadrilateral and octagon coordinates to reduce this dimension from 10n to 6n. As an application, we show that quadrilateral-octagon coordinates can be used exclusively in the streamlined 3-sphere recognition algorithm of Jaco, Rubinstein and Thompson, reducing experimental running times by factors of thousands. We also introduce joint coordinates, a system with only 3n dimensions for octagonal almost normal surfaces that has appealing geometric properties.Comment: 34 pages, 20 figures; v2: Simplified the proof of Theorem 4.5 using cohomology, plus other minor changes; v3: Minor housekeepin

An optical fiber hydrogen sensor using a palladium-coated ball lens

A self-referenced optical fiber refractometer using a ball lens as a sensor head has been developed and characterized. A 350-μm ball lens created at the tip of a single mode fiber has been coated with a 40-nm optically thin layer of palladium that reacts with hydrogen to form a hydride, which has a lower reflectivity than pure palladium. Optical reflectance measurements from the tip of the ball lens were performed to determine the hydrogen response. The change in reflectivity is proportional to the hydrogen concentration in the range 0% to 1% hydrogen in air with a detection limit down to 10 ppm (1σ) in air. This technique offers a simple sensor head arrangement, with a larger sampling area (~40 times) than a typical single-mode fiber core. A statistical image analysis of a palladium film, with cracks created by accelerated failure, confirms that the anticipated sensor area for a ball lens sensor head has a more predictable reflectivity than that of a bare fiber core

Expression proteomics identifies biochemical adaptations and defense responses in transgenic plants with perturbed polyamine metabolism

AbstractSoluble proteins from leaves of transgenic tobacco plants with perturbed polyamine metabolism, caused by S-adenosylmethionine decarboxylase overexpression, were analysed by comparative proteomics. A group of proteins was found to be increasingly repressed, in parallel with the degree of polyamine perturbation, in each of the three independent transgenic lines. These were identified as isoforms of chloroplast ribonucleoproteins, known to be involved in chloroplast mRNA stability, processing and translation. Another group of eight proteins strongly induced in the most metabolically perturbed line was identified as multiple, uncharacterised isoforms of the defense protein PR-1, a known marker for systemic acquired resistance

Teraflop per second gravitational lensing ray-shooting using graphics processing units

Gravitational lensing calculation using a direct inverse ray-shooting approach is a computationally expensive way to determine magnification maps, caustic patterns, and light-curves (e.g. as a function of source profile and size). However, as an easily parallelisable calculation, gravitational ray-shooting can be accelerated using programmable graphics processing units (GPUs). We present our implementation of inverse ray-shooting for the NVIDIA G80 generation of graphics processors using the NVIDIA Compute Unified Device Architecture (CUDA) software development kit. We also extend our code to multiple-GPU systems, including a 4-GPU NVIDIA S1070 Tesla unit. We achieve sustained processing performance of 182 Gflop/s on a single GPU, and 1.28 Tflop/s using the Tesla unit. We demonstrate that billion-lens microlensing simulations can be run on a single computer with a Tesla unit in timescales of order a day without the use of a hierarchical tree code.Comment: 21 pages, 4 figures, submitted to New Astronom