Atmospheric aerosols play a substantial role in climate change through radiative forcing. Combustion-produced carbonaceous particles are the main light-absorbing aerosols; thus, quantifying their optical properties is essential for determining the magnitude of direct forcing. By using the electron energy-loss spectrum in the transmission electron microscope, we quantified the optical properties of individual, submicrometer amorphous carbon spheres that are ubiquitous in East Asian-Pacific outflow. The data indicate that these common spheres are brown, not black, with a mean refractive index of 1.67 - 0.27i (where i = square root 1) at a wavelength of 550 nanometers. The results suggest that brown carbon aerosols should be explicitly included in radiative forcing models.

[1] During Transport and Chemical Evolution over the Pacific (TRACE-P) and Asian Aerosol Characterization Experiment (ACE-Asia) we measured the dry size distribution of Asian aerosols, their state of mixing, and the optical properties of dust, black carbon (BC) and other aerosol constituents in combustion and/or dust plumes. Optical particle sizing in association with thermal heating extracted volatile components and resolved sizes for dust and refractory soot that usually dominated light absorption. BC was internally mixed with volatile aerosol in $85% of accumulation mode particles and constituted $5-15% of their mass. These optically effective sizes constrained the soot and dust size distributions and the imaginary part of the dust refractive index, k, to 0.0006 ± 0.0001. This implies a single-scatter albedo, v (550 nm), for dust ranging from 0.99+ for D p < 1 mm to $0.90 at D p = 10 mm and a size-integrated campaign average near 0.97 ± 0.01. The typical mass scattering efficiency for the dust was $0.3 m 2 g À1 , and the mass absorption efficiency (MAE) was 0.009 m 2 g À1 . Less dust south of 25°N and stronger biomass burning signatures resulted in lower values for v of $0.82 in plumes aloft. Chemically inferred elemental carbon was moderately correlated with BC light absorption (R 2 = 0.40), while refractory soot volume between 0.1 and 0.5 mm was highly correlated (R 2 = 0.79) with absorption. However, both approaches yield an MAE for BC mixtures of $7 ± 2 m 2 g À1 and higher than calculated MAE values for BC of 5 m 2 g À1 . The increase in the mass fraction of soot and BC in pollution aerosol in the presence of elevated dust appears to be due to uptake of the volatile components onto the coarse dust. This predictably lowered v for the accumulation mode from 0.84 in typical pollution to $0.74 in high-dust events. A chemical transport model revealed good agreement between model and observed BC absorption for most of SE Asia and in biomass plumes but underestimated BC for combustion sources north of 25°N by a factor of $3.

Based on a quantum analysis of two capacitively coupled current-biased Josephson junctions, we propose two fundamental two-qubit quantum logic gates. Each of these gates, when supplemented by single-qubit operations, is sufficient for universal quantum computation. Numerical solutions of the time-dependent Schrödinger equation demonstrate that these operations can be performed with good fidelity. The current-biased Josephson junction is an easily fabricated device with great promise as a scalable solid-state qubit [1], as demonstrated by the recent observations of Rabi oscillations [2,3]. This phase qubit is controlled through manipulation of the bias currents and application of microwave pulses resonant with the energy level splitting [2].In this Letter we analyze the quantum dynamics of two coupled phase qubits. (The classical dynamics of this system has also been studied recently [4]). We identify two quantum logic gates that, together with single-qubit operations, provide all necessary ingredients for a universal quantum computer. We perform full dynamical simulations of these gates through numerical integration of the time-dependent Schrödinger equation. These two-qubit operations may be experimentally probed with the methods already used to observe single junction Rabi oscillations [2,3]. Such experiments are of fundamental importance: the successful demonstration of macroscopic quantum entanglement holds profound implications for the universal validity of quantum mechanics [5]. Important progress toward this goal are the temporal oscillations of coupled charge qubits [6] and spectroscopic measurements [7] on the system considered here. Finally, our methods are applicable to the other promising superconducting proposals based on charge, flux, and hybrid realizations [8].Figure 1(a) shows the circuit diagram of our coupled qubits. Each junction has characteristic capacitance C J and critical current I c , and they are coupled by capacitance C C . The two degrees of freedom of this system are the phase differences γ 1 and γ 2 , with dynamics governed by the Hamiltonian [9]Here we have employed the charging and Josephson energies E C = e 2 /2C J and E J = I c /2e, the normalized bias currents J 1 = I 1 /I c , J 2 = I 2 /I c , and the dimensionless coupling parameter ζ = C C /(C C + C J ). This coupling scheme has been recently analyzed [9, 10, 11] and results in a system with easily tuned energy levels and adjustable effective coupling. While ζ is typically fixed by fabrication, the energy levels and the effective coupling of the associated eigenstates are under experimental control through J 1 and J 2 . As shown below, the two junctions are decoupled for J 1 and J 2 sufficiently different, but if J 1 and J 2 are related in certain ways, the junctions are maximally coupled. To illustrate this method of control, we define a reference bias current J 0 and consider the variation of J 1 and J 2 through a detuning parameter ǫ:Quantum logic gates are implemented by varying ǫ with time as shown in Fig. 1(b). This ra...

We present spectroscopic evidence for the creation of entangled macroscopic quantum states in two current-biased Josephson-junction qubits coupled by a capacitor. The individual junction bias currents are used to control the interaction between the qubits by tuning the energy level spacings of the junctions in and out of resonance with each other. Microwave spectroscopy in the 4 to 6 gigahertzrange at 20 millikelvin reveals energy levels that agree well with theoretical results for entangled states. The single qubits are spatially separate, and the entangled states extend over the 0.7-millimeter distance between the two qubits.

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Abstract. Sulfate aerosol particles containing soot aggregates were observed in the marine troposphere in both hemispheres under conditions that ranged from extremely clean to heavily polluted. Even in clean air above the remote Southern Ocean during the First Aerosol Characterization Experiment (ACE 1), depending on the sample, between 10 and 45% of sulfate particles contained soot inclusions. We identified aircraft emissions and biomass burning as the most likely major sources of soot. Internally mixed soot and sulfate appear to comprise a globally significant fraction of aerosols in the troposphere. Anthropogenic combustion aerosols can thus potentially change the radiative climate effects of sulfate aerosols and may have an impact on cloud properties even in the remote troposphere.

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A novel technique is presented for interpreting magnetic field-dependent Hall data at magnetic fields below the range at which Shubnikov–de Haas oscillations occur. The technique generates a ‘‘mobility spectrum’’ in which the maximum carrier density or maximum conductivity is determined as a continuous function of mobility. Examples of the use of the technique with synthetic data as well as data from HgCdTe and GaAs/AlGaAs samples are provided. Other uses of the procedure, including measurement of Fermi surface shapes and direct measurement of the distribution of relaxation times, are discussed.