Sub-Poissonian Shot Noise In A Diffusive Conductor

A review is given of the shot-noise properties of metallic, diffusive conductors. The shot noise is one third of the Poisson noise, due to the bimodal distribution of transmission eigenvalues. The same result can be obtained from a semiclassical calculation. Starting from Oseledec's theorem it is shown that the bimodal distribution is required by Ohm's law.Comment: 9 pages, LaTeX, including 2 figure

Doubled Shot Noise In Disordered Normal-Metal-Superconductor Junctions

The low-frequency shot-noise power of a normal-metal-superconductor junction is studied for arbitrary normal region. Through a scattering approach, a formula is derived which expresses the shot-noise power in terms of the transmission eigenvalues of the normal region. The noise power divided by the current is enhanced by a factor two with respect to its normal-state value, due to Cooper-pair transport in the superconductor. For a disordered normal region, it is still smaller than the Poisson noise, as a consequence of noiseless open scattering channels.Comment: 4 pages, RevTeX v3.0, including 1 figure, Submitted to Physical Review

Classical Optimizers for Noisy Intermediate-Scale Quantum Devices

We present a collection of optimizers tuned for usage on Noisy Intermediate-Scale Quantum (NISQ) devices. Optimizers have a range of applications in quantum computing, including the Variational Quantum Eigensolver (VQE) and Quantum Approximate Optimization (QAOA) algorithms. They are also used for calibration tasks, hyperparameter tuning, in machine learning, etc. We analyze the efficiency and effectiveness of different optimizers in a VQE case study. VQE is a hybrid algorithm, with a classical minimizer step driving the next evaluation on the quantum processor. While most results to date concentrated on tuning the quantum VQE circuit, we show that, in the presence of quantum noise, the classical minimizer step needs to be carefully chosen to obtain correct results. We explore state-of-the-art gradient-free optimizers capable of handling noisy, black-box, cost functions and stress-test them using a quantum circuit simulation environment with noise injection capabilities on individual gates. Our results indicate that specifically tuned optimizers are crucial to obtaining valid science results on NISQ hardware, and will likely remain necessary even for future fault tolerant circuits

VLT/VIMOS Observations of an Occulting Galaxy Pair: Redshifts and Effective Extinction Curve

We present VLT/VIMOS IFU observations of an occulting galaxy pair previously discovered in HST observations. The foreground galaxy is a low-inclination spiral disk, which causes clear attenuation features seen against the bright bulge and disk of the background galaxy. We find redshifts of $z=0.064 \pm0.003$ and z=0.065 for the foreground and background galaxy respectively. This relatively small difference does not rule out gravitational interaction between the two galaxies. Emission line ratios point to a star-forming, not AGN-dominated foreground galaxy. We fit the Cardelli, Clayton & Mathis (CCM) extinction law to the spectra of individual fibres to derive slope ($R_V$) and normalization ($A_V$). The normalization agrees with the HST attenuation map and the slope is lower than the Milky Way relation ($R_V<3.1$), which is likely linked to the spatial sampling of the disk. We speculate that the values of $R_V$ point to either coherent ISM structures in the disk larger than usual ($\sim9$ kpc) or higher starting values of $R_V$, indicative of recent processing of the dust. The foreground galaxy is a low stellar mass spiral ($M_* \sim 3 \times 10^9 M_\odot$) with a high dust content ($M_{\rm dust} \sim 0.5 \times 10^6 M_\odot$). The dust disk geometry visible in the HST image would explain the observed SED properties of smaller galaxies: a lower mean dust temperature, a high dust-to-stellar mass ratio but relatively little optical attenuation. Ongoing efforts to find occulting pairs with a small foreground galaxies will show how common this geometry is.Comment: 16 pages, 3 tables, 13 figures, accepted for publication in MNRA