1,314 research outputs found
Optimal time for sensing in open quantum systems
We study the time-dependent quantum Fisher information (QFI) in an open
quantum system satisfying the Gorini-Kossakowski-Sudarshan-Lindblad master
equation. We also study the dynamics of the system from an effective
non-Hermitian dynamics standpoint and use it to understand the scaling of the
QFI when multiple probes are used. A focus of our work is how the QFI is
maximized at certain times suggesting that the best precision in parameter
estimation can be achieved by focusing on these times. The propagation of
errors analysis allows us to confirm and better understand this idea. We also
propose a parameter estimation procedure involving relatively low resource
consuming measurements followed by higher resource consuming measurements and
demonstrate it in simulation.Comment: 11 pages,8 Figure
Fast-forwarding quantum simulation with real-time quantum Krylov subspace algorithms
Quantum subspace diagonalization (QSD) algorithms have emerged as a
competitive family of algorithms that avoid many of the optimization pitfalls
associated with parameterized quantum circuit algorithms. While the vast
majority of the QSD algorithms have focused on solving the eigenpair problem
for ground, excited-state, and thermal observable estimation, there has been a
lot less work in considering QSD algorithms for the problem of quantum
dynamical simulation. In this work, we propose several quantum Krylov
fast-forwarding (QKFF) algorithms capable of predicting long-time dynamics well
beyond the coherence time of current quantum hardware. Our algorithms use
real-time evolved Krylov basis states prepared on the quantum computer and a
multi-reference subspace method to ensure convergence towards high-fidelity,
long-time dynamics. In particular, we show that the proposed multi-reference
methodology provides a systematic way of trading off circuit depth with
classical post-processing complexity. We also demonstrate the efficacy of our
approach through numerical implementations for several quantum chemistry
problems including the calculation of the auto-correlation and dipole moment
correlation function
Increasing physical activity in older adults using STARFISH, an interactive smartphone application (app); a pilot study
Background:Increasing physical activity in older adults has preventative and therapeutic health benefits. We have developed STARFISH, a smartphone application, to increase physical activity. This paper describes the features of STARFISH, presents the views of older users on the acceptability and usability of the app and reports the results of a six week pilot study of the STARFISH app in older adults. Methods:The operationalisation of the behaviour change techniques (BCTs) within the STARFISH app was mapped against the BCT Taxonomy of Michie et al. Sixteen healthy older adults (eight women and eight men; age 71.1 ± 5.2 years) used the app, in groups of four, for six weeks. Focus groups explored the user experience and objective measure of steps per day recorded. Results:Participants were very positive about using the STARFISH app, in particular the embedded BCTs of self-monitoring, feedback and social support (in the form of group rewards). Objective step data, available for eight participants, showed that step counts increased by an average of 14% (p = 0.077, d = 0.56). Conclusion:The STARFISH app was acceptable and straightforward to use for older adults. STARFISH has potential to increase physical activity in older adults; however, a fully powered randomised controlled trial is required
Calculating Nonlocal Optical Properties of Structures with Arbitrary Shape
In a recent Letter [Phys. Rev. Lett. 103, 097403 (2009)], we outlined a
computational method to calculate the optical properties of structures with a
spatially nonlocal dielectric function. In this Article, we detail the full
method, and verify it against analytical results for cylindrical nanowires.
Then, as examples of our method, we calculate the optical properties of Au
nanostructures in one, two, and three dimensions. We first calculate the
transmission, reflection, and absorption spectra of thin films. Because of
their simplicity, these systems demonstrate clearly the longitudinal (or
volume) plasmons characteristic of nonlocal effects, which result in anomalous
absorption and plasmon blueshifting. We then study the optical properties of
spherical nanoparticles, which also exhibit such nonlocal effects. Finally, we
compare the maximum and average electric field enhancements around nanowires of
various shapes to local theory predictions. We demonstrate that when nonlocal
effects are included, significant decreases in such properties can occur.Comment: 30 pages, 12 figures, 1 tabl
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