Eyes on the Prize: Increasing the Prize May Not Benefit the Contest Organizer in Multiple Online Contests

Given the proliferation of online platforms for crowdsourcing contests, we address the inconsistencies in the extant literature about the behavioral effects of increasing the prize awarded by contest organizers. We endeavor to resolve these inconsistencies by analyzing user behavior in a highly controlled experimental setting in which users can participate (by exerting real effort rather than stated effort) in multiple online contests that vary only in their prizes. The analysis of the behavior of 731 active participants in our first experiment showed that both participation and effort were non-monotonic with the prize, that the low-prize contest was the most effective for the organizers, and that increasing the prize of the low-prize or high-prize contest by 50% actually decreased the benefits for organizers. Our findings advance theory by providing insight into when and why extrinsic incentives fail to produce the desired effects in crowdsourcing contests

Control Requirements and Benchmarks for Quantum Error Correction

Reaching useful fault-tolerant quantum computation relies on successfully implementing quantum error correction (QEC). In QEC, quantum gates and measurements are performed to stabilize the computational qubits, and classical processing is used to convert the measurements into estimated logical Pauli frame updates or logical measurement results. While QEC research has concentrated on developing and evaluating QEC codes and decoding algorithms, specification and clarification of the requirements for the classical control system running QEC codes are lacking. Here, we elucidate the roles of the QEC control system, the necessity to implement low latency feed-forward quantum operations, and suggest near-term benchmarks that confront the classical bottlenecks for QEC quantum computation. These benchmarks are based on the latency between a measurement and the operation that depends on it and incorporate the different control aspects such as quantum-classical parallelization capabilities and decoding throughput. Using a dynamical system analysis, we show how the QEC control system latency performance determines the operation regime of a QEC circuit: latency divergence, where quantum calculations are unfeasible, classical-controller limited runtime, or quantum-operation limited runtime where the classical operations do not delay the quantum circuit. This analysis and the proposed benchmarks aim to allow the evaluation and development of QEC control systems toward their realization as a main component in fault-tolerant quantum computation.Comment: 21+9(SM) pages, 6+3(SM) figure

Electrically tunable multi-terminal SQUID-on-tip

We present a new nanoscale superconducting quantum interference device (SQUID) whose interference pattern can be shifted electrically in-situ. The device consists of a nanoscale four-terminal/four-junction SQUID fabricated at the apex of a sharp pipette using a self-aligned three-step deposition of Pb. In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 $\mu_B/\text{Hz}^{1/2}$ over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging

Quantum-classical processing and benchmarking at the pulse-level

Towards the practical use of quantum computers in the NISQ era, as well as the realization of fault-tolerant quantum computers that utilize quantum error correction codes, pressing needs have emerged for the control hardware and software platforms. In particular, a clear demand has arisen for platforms that allow classical processing to be integrated with quantum processing. While recent works discuss the requirements for such quantum-classical processing integration that is formulated at the gate-level, pulse-level discussions are lacking and are critically important. Moreover, defining concrete performance benchmarks for the control system at the pulse-level is key to the necessary quantum-classical integration. In this work, we categorize the requirements for quantum-classical processing at the pulse-level, demonstrate these requirements with a variety of use cases, including recently published works, and propose well-defined performance benchmarks for quantum control systems. We utilize a comprehensive pulse-level language that allows embedding universal classical processing in the quantum program and hence allows for a general formulation of benchmarks. We expect the metrics defined in this work to form a solid basis to continue to push the boundaries of quantum computing via control systems, bridging the gap between low-level and application-level implementations with relevant metrics.Comment: 22 page

Visualizing Poiseuille flow of hydrodynamic electrons

Hydrodynamics is a general description for the flow of a fluid, and is expected to hold even for fundamental particles such as electrons when inter-particle interactions dominate. While various aspects of electron hydrodynamics were revealed in recent experiments, the fundamental spatial structure of hydrodynamic electrons, the Poiseuille flow profile, has remained elusive. In this work, we provide the first real-space imaging of Poiseuille flow of an electronic fluid, as well as visualization of its evolution from ballistic flow. Utilizing a scanning nanotube single electron transistor, we image the Hall voltage of electronic flow through channels of high-mobility graphene. We find that the profile of the Hall field across the channel is a key physical quantity for distinguishing ballistic from hydrodynamic flow. We image the transition from flat, ballistic field profiles at low temperature into parabolic field profiles at elevated temperatures, which is the hallmark of Poiseuille flow. The curvature of the imaged profiles is qualitatively reproduced by Boltzmann calculations, which allow us to create a 'phase diagram' that characterizes the electron flow regimes. Our results provide long-sought, direct confirmation of Poiseuille flow in the solid state, and enable a new approach for exploring the rich physics of interacting electrons in real space