492,216 research outputs found
A Frequency-Reconfigurable Monopole Antenna with Switchable Stubbed Ground Structure
A frequency-reconfigurable coplanar-waveguide (CPW) fed monopole antenna using switchable stubbed ground structure is presented. Four PIN diodes are employed in the stubs stretching from the ground to make the antenna reconfigurable in three operating modes: a single-band mode (2.4-2.9 GHz), a dual-band mode (2.4-2.9 GHz/5.09-5.47 GHz) and a triple-band mode (3.7-4.26 GHz/5.3-6.3 GHz/8.0-8.8 GHz). The monopole antenna is resonating at 2.4 GHz, while the stubs produce other operating frequency bands covering a number of wireless communication systems, including WLAN, WiMAX, C-band, and ITU. Furthermore, an optimized biasing network has been integrated into this antenna, which has little influence on the performance of the antenna. This paper presents, compares and discusses the simulated and measured results
Experimentally realizable control fields in quantum Lyapunov control
As a hybrid of techniques from open-loop and feedback control, Lyapunov
control has the advantage that it is free from the measurement-induced
decoherence but it includes the system's instantaneous message in the control
loop. Often, the Lyapunov control is confronted with time delay in the control
fields and difficulty in practical implementations of the control. In this
paper, we study the effect of time-delay on the Lyapunov control, and explore
the possibility of replacing the control field with a pulse train or a
bang-bang signal. The efficiency of the Lyapunov control is also presented
through examining the convergence time of the controlled system. These results
suggest that the Lyapunov control is robust gainst time delay, easy to realize
and effective for high-dimensional quantum systems
Effect of Decoherence on the Dynamics of Bose-Einstein Condensates in a Double-well Potential
We study the dynamics of a Bose-Einstein condensate in a double-well
potential in the mean-field approximation. Decoherence effects are considered
by analyzing the couplings of the condensate to environments. Two kinds of
coupling are taken into account. With the first kind of coupling dominated, the
decoherence can enhance the self-trapping by increasing the damping of the
oscillations in the dynamics, while the decoherence from the second kind of
condensate-environment coupling leads to spoiling of the quantum tunneling and
self-trapping.Comment: for color figures, see PR
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