2,916 research outputs found
Random Control over Quantum Open Systems
Parametric fluctuations or stochastic signals are introduced into the control
pulse sequence to investigate the feasibility of random control over quantum
open systems. In a large parameter error region, the out-of-order control
pulses work as well as the regular pulses for dynamical decoupling and
dissipation suppression. Calculations and analysis are based on a
non-perturbative control approach allowed by an exact quantum-state-diffusion
equation. When the average frequency and duration of the pulse sequence take
proper values, the random control sequence is robust, fault- tolerant, and
insensitive to pulse strength deviations and interpulse temporal separation in
the quasi-periodic sequence. This relaxes the operational requirements placed
on quantum control experiments to a great deal.Comment: 7 pages, 6 firgure
Symmetry restoration and quantumness reestablishment
A realistic quantum many-body system, characterized by a generic microscopic
Hamiltonian, is accessible only through approximation methods. The mean field
theories, as the simplest practices of approximation methods, commonly serve as
a powerful tool, but unfortunately often violate the symmetry of the
Hamiltonian. The conventional BCS theory, as an excellent mean field approach,
violates the particle number conservation and completely erases quantumness
characterized by concurrence and quantum discord between different modes. We
restore the symmetry by using the projected BCS theory and the exact numerical
solution and find that the lost quantumness is synchronously reestablished. We
show that while entanglement remains unchanged with the particle numbers,
quantum discord behaves as an extensive quantity with respect to the system
size. Surprisingly, discord is hardly dependent on the interaction strengths.
The new feature of discord offers promising applications in modern quantum
technologies.Comment: 17 pages and 3 figure
Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments.
Many cases of severe environmental contamination arise from historical episodes, where recalcitrant contaminants have resided in the environment for a prolonged time, leading to potentially decreased bioavailability. Use of bioavailable concentrations over bulk chemical levels improves risk assessment and may play a critical role in determining the need for remediation or assessing the effectiveness of risk mitigation operations. In this study, we applied the principle of isotope dilution to quantify bioaccessibility of legacy contaminants DDT and PCBs in marine sediments from a Superfund site. After addition of 13C or deuterated analogues to a sediment sample, the isotope dilution reached a steady state within 24 h of mixing. At the steady state, the accessible fraction (E) derived by the isotope dilution method (IDM) ranged from 0.28 to 0.89 and was substantially smaller than 1 for most compounds, indicating reduced availability of the extensively aged residues. A strong linear relationship (R2=0.86) was found between E and the sum of rapid (Fr) and slow (Fs) desorption fractions determined by sequential Tenax desorption. The IDM-derived accessible concentration (Ce) was further shown to correlate closely with tissue residue in the marine benthic polychaete Neanthes arenaceodentata exposed in the same sediments. As shown in this study, the IDM approach involves only a few simple steps and may be readily adopted in laboratories equipped with mass spectrometers. This novel method is expected to be especially useful for historically contaminated sediments or soils, for which contaminant bioavailability may have changed significantly due to aging and other sequestration processes
Non-perturbative Dynamical Decoupling Control: A Spin Chain Model
This paper considers a spin chain model by numerically solving the exact
model to explore the non-perturbative dynamical decoupling regime, where an
important issue arises recently (J. Jing, L.-A. Wu, J. Q. You and T. Yu,
arXiv:1202.5056.). Our study has revealed a few universal features of
non-perturbative dynamical control irrespective of the types of environments
and system-environment couplings. We have shown that, for the spin chain model,
there is a threshold and a large pulse parameter region where the effective
dynamical control can be implemented, in contrast to the perturbative
decoupling schemes where the permissible parameters are represented by a point
or converge to a very small subset in the large parameter region admitted by
our non-perturbative approach. An important implication of the non-perturbative
approach is its flexibility in implementing the dynamical control scheme in a
experimental setup. Our findings have exhibited several interesting features of
the non-perturbative regimes such as the chain-size independence, pulse
strength upper-bound, noncontinuous valid parameter regions, etc. Furthermore,
we find that our non-perturbative scheme is robust against randomness in model
fabrication and time-dependent random noise
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