Correlated charge noise and relaxation errors in superconducting qubits.

The central challenge in building a quantum computer is error correction. Unlike classical bits, which are susceptible to only one type of error, quantum bits (qubits) are susceptible to two types of error, corresponding to flips of the qubit state about the X and Z directions. Although the Heisenberg uncertainty principle precludes simultaneous monitoring of X- and Z-flips on a single qubit, it is possible to encode quantum information in large arrays of entangled qubits that enable accurate monitoring of all errors in the system, provided that the error rate is low1. Another crucial requirement is that errors cannot be correlated. Here we characterize a superconducting multiqubit circuit and find that charge noise in the chip is highly correlated on a length scale over 600 micrometres; moreover, discrete charge jumps are accompanied by a strong transient reduction of qubit energy relaxation time across the millimetre-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle generation associated with absorption of γ-rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.

Experimental demonstration of an electromagnetic pulse mitigation concept for a laser driven proton source.

The targets that are used to produce high-energy protons with ultra-high intensity lasers generate a strong electromagnetic pulse (EMP). To mitigate that undesired side effect, we developed and tested a concept called the "birdhouse." It consists in confining the EMP field in a finite volume and in dissipating the trapped electromagnetic energy with an electric resistor. A prototype was tested at a 10 TW 50 fs laser facility. The recorded average EMP mitigation ratio is about 20 for frequencies from 100 MHz to 6 GHz. The EMP mitigation ratio attains the level of 50 in the frequency range of 1-2 GHz where microwave emission is maximal. We measured the intensity of proton emission in two directions: along the laser propagation direction and along the edge of the proton beam. We observed that the "birdhouse" induces a two-fold increase of the intensity in the center of the proton beam and a two-fold reduction of the intensity on its edge. We did not observe any modification of the proton beam normalized spectrum.

Erratum: Physics of giant electromagnetic pulse generation in short-pulse laser experiments [Phys. Rev. E 91, 043106 (2015)].

This corrects the article DOI: 10.1103/PhysRevE.91.043106.

Guiding of relativistic electron beams in dense matter by laser-driven magnetostatic fields.

Intense lasers interacting with dense targets accelerate relativistic electron beams, which transport part of the laser energy into the target depth. However, the overall laser-to-target energy coupling efficiency is impaired by the large divergence of the electron beam, intrinsic to the laser-plasma interaction. Here we demonstrate that an efficient guiding of MeV electrons with about 30 MA current in solid matter is obtained by imposing a laser-driven longitudinal magnetostatic field of 600 T. In the magnetized conditions the transported energy density and the peak background electron temperature at the 60-µm-thick target's rear surface rise by about a factor of five, as unfolded from benchmarked simulations. Such an improvement of energy-density flux through dense matter paves the ground for advances in laser-driven intense sources of energetic particles and radiation, driving matter to extreme temperatures, reaching states relevant for planetary or stellar science as yet inaccessible at the laboratory scale and achieving high-gain laser-driven thermonuclear fusion.

Publisher's Note: Dynamic model of target charging by short laser pulse interactions [Phys. Rev. E 92, 043107 (2015)].

This corrects the article DOI: 10.1103/PhysRevE.92.043107.

Dynamic model of target charging by short laser pulse interactions.

A model providing an accurate estimate of the charge accumulation on the surface of a metallic target irradiated by a high-intensity laser pulse of fs-ps duration is proposed. The model is confirmed by detailed comparisons with specially designed experiments. Such a model is useful for understanding the electromagnetic pulse emission and the quasistatic magnetic field generation in laser-plasma interaction experiments.

Physics of giant electromagnetic pulse generation in short-pulse laser experiments.

In this paper we describe the physical processes that lead to the generation of giant electromagnetic pulses (GEMPs) at powerful laser facilities. Our study is based on experimental measurements of both the charging of a solid target irradiated by an ultra-short, ultra-intense laser and the detection of the electromagnetic emission in the GHz domain. An unambiguous correlation between the neutralization current in the target holder and the electromagnetic emission shows that the source of the GEMP is the remaining positive charge inside the target after the escape of fast electrons accelerated by the ultra-intense laser. A simple model for calculating this charge in the thick target case is presented. From this model and knowing the geometry of the target holder, it becomes possible to estimate the intensity and the dominant frequencies of the GEMP at any facility.

Aerobic microbial Fe acquisition from ferrihydrite nanoparticles: effects of crystalline order, siderophores, and alginate.

This research compared the bioavailability of Fe associated with two forms of the hydrous Fe oxyhydroxide nanomineral ferrihydrite (Fh)--the smaller (1-3 nm), less ordered 2-line (2L) phase and the slightly larger, (2-6 nm) more ordered 6-line (6L) phase--to the common aerobic soil bacterium Pseudomonas mendocina ymp. P. mendocina can acquire Fe from minerals using high-affinity Fe(III) binding ligands known as siderophores and a cell-associated metalloreductase that requires direct cell-mineral contact. Wild-type (WT) P. mendocina and a siderophore(-) mutant were used to monitor siderophore -related and -independent Fe acquisition from 2L and 6L Fh. Both WT and mutant strains acquired Fe from Fh, although Fe acquisition and growth were substantially greater on the 2L phase than on the 6L phase. In the absence of bacteria, copious quantities of the biofilm exopolysaccharide alginate slightly promoted dissolution of 2L and 6L Fh. In biotic experiments, added alginate slightly enhanced growth and Fe acquisition from 6L Fh but not from 2L Fh. Recent research has led to an emerging understanding that Fe-oxide nanoparticle structure, stability, and reactivity are highly sensitive to size at the nanoscale; this research emphasizes how subtle differences in nanoparticle size-related properties can also affect bioavailability.

Target charging in short-pulse-laser-plasma experiments.

Interaction of high-intensity laser pulses with solid targets results in generation of large quantities of energetic electrons that are the origin of various effects such as intense x-ray emission, ion acceleration, and so on. Some of these electrons are escaping the target, leaving behind a significant positive electric charge and creating a strong electromagnetic pulse long after the end of the laser pulse. We propose here a detailed model of the target electric polarization induced by a short and intense laser pulse and an escaping electron bunch. A specially designed experiment provides direct measurements of the target polarization and the discharge current in the function of the laser energy, pulse duration, and target size. Large-scale numerical simulations describe the energetic electron generation and their emission from the target. The model, experiment, and numerical simulations demonstrate that the hot-electron ejection may continue long after the laser pulse ends, enhancing significantly the polarization charge.

The x-ray calibration facility of the laser integration line in the 0.9-10 keV range: the high energy x-ray source and some applications.

The laser integration line (LIL) located at CEA-CESTA is equipped with x-ray plasma diagnostics using different kinds of x-ray components such as filters, mirrors, crystals, detectors, and cameras. The CEA-DAM of Arpajon is currently developing x-ray calibration methods and carrying out absolute calibration of LIL x-ray photodetectors. To guarantee LIL measurements, detectors such as x-ray cameras must be regularly calibrated close to the facility. A new x-ray facility is currently available to perform these absolute x-ray calibrations. This paper presents the x-ray tube based high energy x-ray source delivering x-ray energies ranging from 0.9 to 10 keV by means of an anode barrel. The purpose of this source is mainly to calibrate LIL x-ray cameras but it can also be used to measure x-ray filter transmission of plasma diagnostics. Different x-ray absolute calibrations such as x-ray streak and framing camera yields, x-ray charge-coupled device quantum efficiencies, and x-ray filter transmissions are presented in this paper. A x-ray flat photocathode detector sensitivity calibration recently performed for a CEA Z-pinch facility is also presented.

High-pressure phases of calcium: density-functional theory and diffusion quantum Monte Carlo approach.

The phase diagram of Ca is examined using a combination of density-functional theory (DFT) and diffusion quantum Monte Carlo (DMC) calculations. Gibbs free energies of several competing structures are computed at pressures near 50 GPa. Existing disagreements for the stability of Ca both at low and room temperature are resolved with input from DMC. Furthermore, DMC calculations are performed on 0 K crystalline structures up to 150 GPa and it is demonstrated that the widely used generalized gradient approximation of DFT is insufficient to accurately account for the relative stability of the high-pressure phases of Ca. The results indicate that the theoretical phase diagram of Ca needs a revision.

Synthesis and spectroscopic studies of non-heme diiron(III) species with a terminal hydroperoxide ligand: models for hemerythrin.

Two compounds, [Fe2(mu-OH)(mu-Ph4DBA)(TMEDA)2(OTf)] (4) and [Fe2(mu-OH)(mu-Ph4DBA)(DPE)2(OTf)] (7), where Ph4DBA(2-) is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate), have been prepared as synthetic models for the dioxygen-binding non-heme diiron protein hemerythrin (Hr). X-ray crystallography reveals that, in the solid state, these compounds contain the asymmetric coordination environment found at the diiron center in the reduced form of the protein, deoxyHr. Mössbauer spectra of the models (4, delta = 1.21(2), DeltaE(Q) = 2.87(2) mm s(-1); 7, delta(av) = 1.23(1), DeltaE(Qav) = 2.79(1) mm s(-1)) and deoxyHr (delta = 1.19, DeltaE(Q) = 2.81 mm s(-1)) are also in good agreement. Oxygenation of the diiron(II) complexes dissolved in CH2Cl2 containing 3 equiv of N-MeIm (4) or neat EtCN (7) at -78 degrees C affords a red-orange solution with optical bands at 336 nm (7300 M(-1) cm(-1)) and 470 nm (2600 M(-1) cm(-1)) for 4 and at 334 nm (6400 M(-1) cm(-1)) and 484 nm (2350 M(-1) cm(-1)) for 7. These spectra are remarkably similar to that of oxyHr, 330 nm (6800 M(-1) cm(-1)) and 500 nm (2200 M(-1) cm(-1)). The electron paramagnetic resonance (EPR) spectrum of the cryoreduced, mixed-valence dioxygen adduct of 7 displays properties consistent with a (mu-oxo)diiron(II,III) core. An investigation of 7 and its dioxygen-bound adduct by extended X-ray absorption fine structure (EXAFS) spectroscopy indicates that the oxidized species contains a (mu-oxo)diiron(III) core with iron-ligand distances in agreement with those expected for oxide, carboxylate, and amine/hydroperoxide donor atoms. The analogous cobalt complex [Co2(mu-OH)(mu-Ph4DBA)(TMEDA)2(OTf)] (6) was synthesized and structurally characterized, but it was unreactive toward dioxygen.

Catalytic galactose oxidase models: biomimetic Cu(II)-phenoxyl-radical reactivity.

Biomimetic functional models of the mononuclear copper enzyme galactose oxidase are presented that catalytically oxidize benzylic and allylic alcohols to aldehydes with O2 under mild conditions. The mechanistic fidelity between the models and the natural system is pronounced. Modest structural mimicry proves sufficient to transfer an unusual ligand-based radical mechanism, previously unprecedented outside the protein matrix, to a simple chemical system.

Importance of sebaceous glands in cutaneous penetration of an antiandrogen: target effect of liposomes.

The significance of the sebaceous gland pathway in the cutaneous permeation of an antiandrogen, 4-[3-(4-hydroxybutyl)-4,4-dimethyl -2,5-dioxo-1-imidazolidinyl]-2-(trifluoromethyl)benzonitrile (RU 58841), was studied with normal hairless rat skin and an induced scar hairless rat skin without sebaceous glands. RU 58841 was dissolved in an alcoholic solution and encapsulated in liposomes for comparison. After 24 h, the cumulative percentage of RU 58841 absorbed in vitro was 3-4-fold higher in the normal skin than in the scar skin; in the case of liposomes, the accumulation of the drug in the normal dermis was significantly higher than in the scar one. In the in vivo cutaneous distribution, the epidermis and dermis of the normal skin contained higher amounts of RU 58841 than the scar skin (ninefold with the solution and 16-fold with liposomes). An autoradiography study showed that with the solution, the drug was mainly localized in the stratum corneum/epidermis, and with the liposomes, the drug was mainly localized in the sebaceous glands. We concluded that the sebaceous glands constituted the main pathway for RU 58841. The alcoholic solution encouraged the localization of the drug into the stratum corneum, whereas liposomes targeted the sebaceous glands.

Preparation and characterization of dipalmitoylphosphatidylcholine liposomes containing interleukin-2.

Human recombinant interleukin-2 (IL-2) has been associated or mixed with small unilamellar vesicles prepared from dipalmitoylphosphatidylcholine (DPPC). Whatever the mode of IL-2 introduction, a considerable proportion of the added protein was associated with the liposomes, as determined by gel filtration and ultrafiltration/centrifugation, suggesting that IL-2 can interact with the lipid bilayer as well as being entrapped within the aqueous phase. Moreover, IL-2 prevented the aggregation/fusion of the vesicles at 4 degrees C. Liposome-associated protein was partially protected from digestion by pepsin, especially at the C-terminal, since no fluorescence emission from the tryptophan in this region was detected in the resulting peptides after separation by HPLC. Such systems could constitute a sustained release form of IL-2 for immunotherapy.

Dihydrolicoisoflavone, a new isoflavanone from Swartzia polyphylla.

Fractionation of an ethanolic extract of Swartzia polyphylla, guided in part by an assay for inhibition of protein kinase C, led to the isolation of the known flavonoids biochanin A, dihydrobiochanin A, ferreirin, dalbergioidin, and naringenin, and one new prenylated isoflavonone, dihydrolicoisoflavone [1].

Similarities in the release rates of different drugs from polyethylene glycol 6000 solid dispersions.

The dissolution rates (mg min-1) of 10 drugs, solid dispersed by fusion in polyethylene glycol 6000 (PEG 6000) have been examined by rotating disc methodology. The dispersions generally displayed release rates which were linearly dependent upon the drug concentration (% drug) at high polymer content. However the range over which this linearity was encountered varied unduly, e.g. 0-2% for phenylbutazone and 0-15% for paracetamol. The slope of this line (mean value: 0.451 mg min-1 % -1) was statistically the same for nine of the drugs studied, the exception being griseofulvin which did not form a true solid dispersion but was a microcrystalline dispersion of the drug within the PEG. During fusion, chain scission of the PEG 6000 occurred in the presence of several drugs. PEG 6000 was incompatible with disulfiram, frusemide, chlorothiazide and chlorpropamide.