12,371 research outputs found
Controllability of Quantum Systems
An overview and synthesis of results and criteria for open-loop
controllability of Hamiltonian quantum systems obtained using Lie group and Lie
algebra techniques is presented. Negative results for open-loop controllability
of dissipative systems are discussed, and the superiority of closed-loop
(feedback) control for quantum systems is established.Comment: 6 pages, to appear in Proceedings of Conference on Lagrangian and
Hamiltonian Methods in Non-Linear Control (Seville, Spain, 2003
Using Virtual Addresses with Communication Channels
While for single processor and SMP machines, memory is the allocatable
quantity, for machines made up of large amounts of parallel computing units,
each with its own local memory, the allocatable quantity is a single computing
unit. Where virtual address management is used to keep memory coherent and
allow allocation of more than physical memory is actually available, virtual
communication channel references can be used to make computing units stay
connected across allocation and swapping.Comment: 5 pages, 4 figure
Implementation of Quantum Gates via Optimal Control
Starting with the basic control system model often employed in NMR pulse
design, we derive more realistic control system models taking into account
effects such as off-resonant excitation for systems with fixed inter-qubit
coupling controlled by globally applied electromagnetic fields, as well as for
systems controlled by a combination of a global fields and local control
electrodes. For both models optimal control is used to find controls that
implement a set of two- and three-qubit gates with fidelity greater than
99.99%. While in some cases the optimal pulses obtained appear to be
surprisingly simple and experimentally realistic, the results also show that
the "optimal" pulses obtained in other cases are experimentally infeasible, and
more sophisticated parametrization of the control fields and numerical
algorithms are needed.Comment: 10 pages, 4 figure
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