621 research outputs found
Gating of high-mobility InAs metamorphic heterostructures
We investigate the performance of gate-defined devices fabricated on high
mobility InAs metamorphic heterostructures. We find that heterostructures
capped with InGaAs often show signs of parallel conduction
due to proximity of their surface Fermi level to the conduction band minimum.
Here, we introduce a technique that can be used to estimate the density of this
surface charge that involves cool-downs from room temperature under gate bias.
We have been able to remove the parallel conduction under high positive bias,
but achieving full depletion has proven difficult. We find that by using
InAlAs as the barrier without an InGaAs
capping, a drastic reduction in parallel conduction can be achieved. Our
studies show that this does not change the transport properties of the quantum
well significantly. We achieved full depletion in InAlAs capped
heterostructures with non-hysteretic gating response suitable for fabrication
of gate-defined mesoscopic devices
Correlated errors can lead to better performance of quantum codes
A formulation for evaluating the performance of quantum error correcting
codes for a general error model is presented. In this formulation, the
correlation between errors is quantified by a Hamiltonian description of the
noise process. We classify correlated errors using the system-bath interaction:
local versus nonlocal and two-body versus many-body interactions. In
particular, we consider Calderbank-Shor-Steane codes and observe a better
performance in the presence of correlated errors depending on the timing of the
error recovery. We also find this timing to be an important factor in the
design of a coding system for achieving higher fidelities.Comment: 5 pages, 3 figures. Replaced by the published version. Title change
The galaxy rotation curves in the modified gravity formalism
Astronomical data have shown that the galaxy rotation curves are mostly flat
in the far distance of the galactic cores, which reveals the insufficiency of
our knowledges about how gravity works in these regimes. In this paper we
introduce a resolution of this issue from the modified gravity
formalism perspective. By investigating two classes of models with separable
(minimal coupling model) and inseparable (non-minimal coupling model) parts of
the Ricci scalar and trace of the energy-momentum tensor , we find that
only in the latter models it is possible to attain flat galaxy rotation curves.Comment: 9 pages, 4 figure
Jump-diffusion unravelling of a non Markovian generalized Lindblad master equation
The "correlated-projection technique" has been successfully applied to derive
a large class of highly non Markovian dynamics, the so called non Markovian
generalized Lindblad type equations or Lindblad rate equations. In this
article, general unravellings are presented for these equations, described in
terms of jump-diffusion stochastic differential equations for wave functions.
We show also that the proposed unravelling can be interpreted in terms of
measurements continuous in time, but with some conceptual restrictions. The
main point in the measurement interpretation is that the structure itself of
the underlying mathematical theory poses restrictions on what can be considered
as observable and what is not; such restrictions can be seen as the effect of
some kind of superselection rule. Finally, we develop a concrete example and we
discuss possible effects on the heterodyne spectrum of a two-level system due
to a structured thermal-like bath with memory.Comment: 23 page
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