36 research outputs found
Fast quantum control in dissipative systems using dissipationless solutions
We report on a systematic geometric procedure, built up on solutions designed
in the absence of dissipation, to mitigate the effects of dissipation in the
control of open quantum systems. Our method addresses a standard class of open
quantum systems modeled by non-Hermitian Hamiltonians. It provides the
analytical expression of the extra magnetic field to be superimposed to the
driving field in order to compensate the geometric distortion induced by
dissipation, and produces an exact geometric optimization of fast population
transfer. Interestingly, it also preserves the robustness properties of
protocols originally optimized against noise. Its extension to two interacting
spins restores a fidelity close to unity for the fast generation of Bell state
in the presence of dissipation
Fine-grained fault-tolerance : reliability as a fungible resource
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 131-134).The traditional design of logic circuits, based on reliable components, is incompatible with the next generation of devices relying on fewer resources and subject to high rates of soft errors. These allow a trade-off between failure probability and their space and power consumption. Using this, we show that reliability can be a fungible resource, interconvertible with other physical resources in multiple, unusual ways, via fault-tolerant architectures. This thesis investigates the potentialities offered by a fault-tolerant design in devices whose reliability is limited by shrinking resources. Surprisingly, we find that an appropriate use of structured redundancy could lead to more efficient components. The performance of a fine-grained multiplexed design can indeed be systematically evaluated in terms of resource savings and reliability improvement. This analysis is applied to characterize technologies at the nano scale, such as molecular electronics, which may benefit enormously by fault-tolerant designs.by François Impens.S.M
Toward a test of angular momentum coherence in a twin-atom interferometer
We present a scheme well-suited to investigate quantitatively the angular
momentum coherence of molecular fragments. Assuming that the dissociated
molecule has a null total angular momentum, we investigate the propagation of
the corresponding atomic fragments in the apparatus. We show that the
envisioned interferometer enables one to distinguish unambiguously a
spin-coherent from a spin-incoherent dissociation, as well as to estimate the
purity of the angular momentum density matrix associated with the fragments.
This setup, which may be seen as an atomic analogue of a twin-photon
interferometer, can be used to investigate the suitability of molecule
dissociation processes -- such as the metastable hydrogen atoms H()-H() dissociation - for coherent twin-atom optics.Comment: 6 pages, 3 Figures. Final version accepted for publication in
Europhysics Letter