108,888 research outputs found
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
Photonic band structure of ZnO photonic crystal slab laser
We recently reported on the first realization of ultraviolet photonic crystal
laser based on zinc oxide [Appl. Phys. Lett. {\bf 85}, 3657 (2004)]. Here we
present the details of structural design and its optimization. We develop a
computational super-cell technique, that allows a straightforward calculation
of the photonic band structure of ZnO photonic crystal slab on sapphire
substrate. We find that despite of small index contrast between the substrate
and the photonic layer, the low order eigenmodes have predominantly
transverse-electric (TE) or transverse-magnetic (TM) polarization. Because
emission from ZnO thin film shows strong TE preference, we are able to limit
our consideration to TE bands, spectrum of which can possess a complete
photonic band gap with an appropriate choice of structure parameters. We
demonstrate that the geometry of the system may be optimized so that a sizable
band gap is achieved.Comment: 8 pages, 7 figure
Effects of uncertainties and errors on Lyapunov control
Lyapunov control (open-loop) is often confronted with uncertainties and
errors in practical applications. In this paper, we analyze the robustness of
Lyapunov control against the uncertainties and errors in quantum control
systems. The analysis is carried out through examinations of uncertainties and
errors, calculations of the control fidelity under influences of the
certainties and errors, as well as discussions on the caused effects. Two
examples, a closed control system and an open control system, are presented to
illustrate the general formulism.Comment: 4 pages, 5 figure
- …