1,979 research outputs found
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 () in a galaxy
with an extended HI gas disk are as large as , where
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 . 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
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
- …