Experimentally efficient methods for estimating the performance of quantum measurements

Efficient methods for characterizing the performance of quantum measurements are important in the experimental quantum sciences. Ideally, one requires both a physically relevant distinguishability measure between measurement operations and a well-defined experimental procedure for estimating the distinguishability measure. Here, we propose the average measurement fidelity and error between quantum measurements as distinguishability measures. We present protocols for obtaining bounds on these quantities that are both estimable using experimentally accessible quantities and scalable in the size of the quantum system. We explain why the bounds should be valid in large generality and illustrate the method via numerical examples.Comment: 20 pages, 1 figure. Expanded details and typos corrected. Accepted versio

Large Force Fluctuations in a Flowing Granular Medium

We report the characteristics of the temporal fluctuations in the local force delivered to the wall of a 2D hopper by a granular medium flowing through it. The forces are predominantly impulsive at all flow rates for which the flow does not permanently jam. The average impulse delivered to the wall is much larger than the momentum acquired by a single particle under gravity between collisions, reflecting the fact that momentum is transferred to the walls from the bulk of the flow by collisions. At values larger than the average impulse, the probability distribution of impulses is broad and decays exponentially on the scale of the average impulse, just as it does in static granular media. At small impulse values, the probability distribution evolves continuously with flow velocity but does not show a clear signature of the transition from purely collisional flow to intermittently jamming flows. However, the time interval between collisions tends to a power law distribution, $P(\tau)\sim \tau^{-3/2}$, thus showing a clear dynamical signature of the approach to jamming.Comment: 4 pages, 3 figure

Time-resolved magnetic sensing with electronic spins in diamond

Quantum probes can measure time-varying fields with high sensitivity and spatial resolution, enabling the study of biological, material, and physical phenomena at the nanometer scale. In particular, nitrogen-vacancy centers in diamond have recently emerged as promising sensors of magnetic and electric fields. Although coherent control techniques have measured the amplitude of constant or oscillating fields, these techniques are not suitable for measuring time-varying fields with unknown dynamics. Here we introduce a coherent acquisition method to accurately reconstruct the temporal profile of time-varying fields using Walsh sequences. These decoupling sequences act as digital filters that efficiently extract spectral coefficients while suppressing decoherence, thus providing improved sensitivity over existing strategies. We experimentally reconstruct the magnetic field radiated by a physical model of a neuron using a single electronic spin in diamond and discuss practical applications. These results will be useful to implement time-resolved magnetic sensing with quantum probes at the nanometer scale.Comment: 8+12 page

Maximizing Wealth and Happiness: Improving Investor Decisions Through Improved Affective Forecasting

Business: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)Investor behavior has long been plagued by a conservatism that keeps individuals from maximizing their wealth. We examine how experience and explicit feedback can reduce two of the main impediments to successful investor decision making: loss aversion and myopia. Consistent with Kermer’s et al. (2006) claim that loss aversion is a symptom of poor affective forecasting, we are able to demonstrate that poor affective forecasting undermines investor decision-making by fueling loss aversion and inspiring myopic and suboptimal investment decisions. Importantly, we are also able to show that explicit feedback illustrating the gap between an individual’s affective forecast and actual affective response reduces affective forecasting errors. Once investors become better affective forecasters, they are less inclined to fear a temporary setback, which is observed through reduced loss aversion and investment decisions that focus on maximizing long-term earnings. In other words, improving affective forecasting can help consumers maximize both wealth and happiness.A three-year embargo was granted for this item