Universal fault-tolerant quantum computers will require error-free execution of long sequences of quantum gate operations, which is expected to involve millions of physical qubits. Before the full power of such machines will be available, near-term quantum devices will provide several hundred qubits and limited error correction. Still, there is a realistic prospect to run useful algorithms within the limited circuit depth of such devices. Particularly promising are optimization algorithms that follow a hybrid approach: the aim is to steer a highly entangled state on a quantum system to a target state that minimizes a cost function via variation of some gate parameters. This variational approach can be used both for classical optimization problems as well as for problems in quantum chemistry. The challenge is to converge to the target state given the limited coherence time and connectivity of the qubits. In this context, the quantum volume as a metric to compare the power of near-term quantum devices is discussed.With focus on chemistry applications, a general description of variational algorithms is provided and the mapping from fermions to qubits is explained. Coupledcluster and heuristic trial wave-functions are considered for efficiently finding molecular ground states. Furthermore, simple error-mitigation schemes are introduced that could improve the accuracy of determining ground-state energies. Advancing these techniques may lead to near-term demonstrations of useful quantum computation with systems containing several hundred qubits.PACS numbers: quantum computation, quantum chemistry, quantum algorithms

The root-mean-square (rms) nuclear charge radius of 8 He, the most neutron-rich of all particlestable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6 He was measured to be 2.068(11) fm, in excellent agreement with a previous result.The significant reduction in charge radius from 6 He to 8 He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8 He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations. * Electronic address: pmueller@anl.gov 1

Aim. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution.Methods. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands.Results. The sample average values for the radio scale heights of the halo are 1.1 ± 0.3 kpc in C-band and 1.4 ± 0.7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h˜ which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h˜ shows a tight anticorrelation with the mass surface density.Conclusions. The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk.

Abstract. The combination of dispersion measures of pulsars, distances from the model of Cordes & Lazio (2002) and emission measures from the WHAM survey enabled a statistical study of electron densities and filling factors of the diffuse ionized gas (DIG) in the Milky Way. The emission measures were corrected for absorption and contributions from beyond the pulsar distance. For a sample of 157 pulsars at |b| > 5• and 60• , located in mainly interarm regions within about 3 kpc from the Sun, we find that: (1) The average volume filling factor along the line of sight f v and the mean density in ionized clouds nc are inversely correlated: f v (nc) = (0.0184 ± 0.0011)n −1.07±0.03 c for the ranges 0.03 < nc < 2 cm −3 and 0.8 > f v > 0.01. This relationship is very tight. The inverse correlation of f v and nc causes the well-known constancy of the average electron density along the line of sight. As f v (z) increases with distance from the Galactic plane |z|, the average size of the ionized clouds increases with |z|. (2) For |z| < 0.9 kpc the local density in clouds nc(z) and local filling factor f (z) are inversely correlated because the local electron density ne(z) = f (z)nc(z) is constant. We suggest that f (z) reaches a maximum value of > 0.3 near |z| = 0.9 kpc, whereas nc(z) continues to decrease to higher |z|, thus causing the observed flattening in the distribution of dispersion measures perpendicular to the Galactic plane above this height. (3) For |z| < 0.9 kpc the local distributions nc(z), f(z) and n 2 e (z) have the same scale height which is in the range 250 < h < ∼ 500 pc. (4) The average degree of ionization of the warm atomic gas Iw(z) increases towards higher |z| similarly to f v (z). Towards |z| = 1 kpc, f v (z) = 0.24 ± 0.05 and Iw(z) = 0.24 ± 0.02. Near |z| = 1 kpc most of the warm, atomic hydrogen is ionized.

Measurements of 81Kr/Kr in deep groundwater from the Nubian Aquifer (Egypt) were performed by a new laser‐based atom‐counting method. 81Kr ages range from ∼2 × 105 to ∼1 × 106 yr, correlate with 36Cl/Cl ratios, and are consistent with lateral flow of groundwater from a recharge area near the Uweinat Uplift in SW Egypt. Low δ2H values of the 81Kr‐dated groundwater reveal a recurrent Atlantic moisture source during Pleistocene pluvial periods. These results indicate that the 81Kr method for dating old groundwater is robust and such measurements can now be applied to a wide range of hydrologic problems.

Background: Octupole-deformed nuclei, such as that of 225 Ra, are expected to amplify observable atomic electric dipole moments (EDMs) that arise from time-reversal and parity-violating interactions in the nuclear medium. In 2015, we reported the first "proof-of-principle" measurement of the 225 Ra atomic EDM.Purpose: This work reports on the first of several experimental upgrades to improve the statistical sensitivity of our 225 Ra EDM measurements by orders of magnitude and evaluates systematic effects that contribute to current and future levels of experimental sensitivity. Method: Laser-cooled and trapped225 Ra atoms are held between two high voltage electrodes in an ultra high vacuum chamber at the center of a magnetically shielded environment. We observe Larmor precession in a uniform magnetic field using nuclear-spin-dependent laser light scattering and look for a phase shift proportional to the applied electric field, which indicates the existence of an EDM. The main improvement to our measurement technique is an order of magnitude increase in spin precession time, which is enabled by an improved vacuum system and a reduction in trap-induced heating. Results: We have measured the225 Ra atomic EDM to be less than 1.4 × 10 −23 e cm (95% confidence upper limit), which is a factor of 36 improvement over our previous result. Conclusions:Our evaluation of systematic effects shows that this measurement is completely limited by statistical uncertainty. Combining this measurement technique with planned experimental upgrades we project a statistical sensitivity at the 1 × 10 −28 e cm level and a total systematic uncertainty at the 4 × 10 −29 e cm level.

We have performed precision laser spectroscopy on individual 6He (t(1/2)=0.8 s) atoms confined and cooled in a magneto-optical trap, and measured the isotope shift between 6He and 4He to be 43 194.772+/-0.056 MHz for the 2(3)S1-3(3)P2 transition. Based on this measurement and atomic theory, the nuclear charge radius of 6He is determined for the first time in a method independent of nuclear models to be 2.054+/-0.014 fm. The result is compared with the values predicted by a number of nuclear structure calculations and tests their ability to characterize this loosely bound halo nucleus.

Transient electroluminescence ͑EL͒ from single-and multilayer organic light-emitting diodes ͑OLEDs͒ was investigated by driving the devices with short, rectangular voltage pulses. The single-layer devices consist of indium-tin oxide ͑ITO͒/tris͑8-hydroxy-quinoline͒aluminum ͑Alq 3 ͒/magnesium ͑Mg͒:silver ͑Ag͒, whereas the structure of the multilayer OLEDs are ITO/copper phthalocyanine ͑CuPc͒/N,NЈ-di͑naphthalene-1-yl͒-N,NЈ-diphenyl-benzidine ͑NPB͒/Alq 3 /Mg:Ag. Apparent model-dependent values of the electron mobility ( e ) in Alq 3 have been calculated from the onset of EL for both device structures upon invoking different internal electric field distributions. For the single-layer OLEDs, transient experiments with different dc bias voltages indicated that the EL delay time is determined by the accumulation of charge carriers inside the device rather than by transport of the latter. This interpretation is supported by the observation of delayed EL after the voltage pulse is turned off. In the multilayer OLED the EL onset-dependent on the electric field-is governed by accumulated charges ͑holes͒ at the internal organic-organic interface (NPB/Alq 3 ) or is transport limited. Time-of-flight measurements on 150-nm-thin Alq 3 layers yield weak field-dependent e values of the order of 1ϫ10 Ϫ5 cm 2 /Vs at electrical fields between 3.9ϫ10 5 and 1.3ϫ10 6 V/cm.