Counteracting systems of diabaticities using DRAG controls: The status after 10 years

The task of controlling a quantum system under time and bandwidth limitations is made difficult by unwanted excitations of spectrally neighboring energy levels. In this article we review the Derivative Removal by Adiabatic Gate (DRAG) framework. DRAG is a multi-transition variant of counterdiabatic driving, where multiple low-lying gapped states in an adiabatic evolution can be avoided simultaneously, greatly reducing operation times compared to the adiabatic limit. In its essence, the method corresponds to a convergent version of the superadiabatic expansion where multiple counterdiabaticity conditions can be met simultaneously. When transitions are strongly crowded, the system of equations can instead be favorably solved by an average Hamiltonian (Magnus) expansion, suggesting the use of additional sideband control. We give some examples of common systems where DRAG and variants thereof can be applied to improve performance.Comment: 7 pages, 2 figure

Impact of dark matter subhalos on extended HI disks of galaxies: Possible formation of HI fine structures and stars

Recent observations have discovered star formation activities in the extreme outer regions of disk galaxies. However it remains unclear what physical mechanisms are responsible for triggering star formation in such low-density gaseous environments of galaxies. In order to understand the origin of these outer star-forming regions, we numerically investigate how the impact of dark matter subhalos orbiting a gas-rich disk galaxy embedded in a massive dark matter halo influences the dynamical evolution of outer HI gas disk of the galaxy. We find that if the masses of the subhalos ($M_{\rm sb}$) in a galaxy with an extended HI gas disk are as large as $10^{-3} \times M_{\rm h}$, where $M_{\rm h}$ is the total mass of the galaxy's dark halo, local fine structures can be formed in the extended HI disk. We also find that the gas densities of some apparently filamentary structures can exceed a threshold gas density for star formation and thus be likely to be converted into new stars in the outer part of the HI disk in some models with larger $M_{\rm sb}$. These results thus imply that the impact of dark matter subhalos (``dark impact'') can be important for better understanding the origin of recent star formation discovered in the extreme outer regions of disk galaxies. We also suggest that characteristic morphologies of local gaseous structures formed by the dark impact can indirectly prove the existence of dark matter subhalos in galaxies. We discuss the origin of giant HI holes observed in some gas-rich galaxies (e.g., NGC 6822) in the context of the dark impact.Comment: 8 pages, 4 figures, accepted by ApJ

Dansk-tysk teknisk ordbog. Fonden for Fagsproglig Leksikografi, Handelshøjskolen i København, og Grafisk Forlag A7S, København 1990. ISBN 87-04451-9. 1. udgave. 413 s.

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Engineering adiabaticity at an avoided crossing with optimal control

We investigate ways to optimize adiabaticity and diabaticity in the Landau-Zener model with non-uniform sweeps. We show how diabaticity can be engineered with a pulse consisting of a linear sweep augmented by an oscillating term. We show that the oscillation leads to jumps in populations whose value can be accurately modeled using a model of multiple, photon-assisted Landau-Zener transitions, which generalizes work by Wubs et al. [New J. Phys. 7, 218 (2005)]. We extend the study on diabaticity using methods derived from optimal control. We also show how to preserve adiabaticity with optimal pulses at limited time, finding a non-uniform quantum speed limit