25,565 research outputs found
Character Formula for Infinite Dimensional Unitarizable Modules of the General Linear Superalgebra
The Fock space of bosonic and fermionic quantum oscillators forms
a unitarizable module of the general linear superalgebra . Its
tensor powers decompose into direct sums of infinite dimensional irreducible
highest weight -modules. We obtain an explicit decomposition of
any tensor power of this Fock space into irreducibles, and develop a character
formula for the irreducible -modules arising in this way.Comment: 25 Pages, LaTeX forma
Finite-horizon H∞ control for discrete time-varying systems with randomly occurring nonlinearities and fading measurements
This technical note deals with the H∞ control problem for a class of discrete time-varying nonlinear systems with both randomly occurring nonlinearities and fading measurements over a finite-horizon. The system measurements are transmitted through fading channels described by a modified stochastic Rice fading model. The purpose of the addressed problem is to design a set of time-varying controllers such that, in the presence of channel fading and randomly occurring nonlinearities, the H∞ performance is guaranteed over a given finite-horizon. The model transformation technique is first employed to simplify the addressed problem, and then the stochastic analysis in combination with the completing squares method are carried out to obtain necessary and sufficient conditions of an auxiliary index which is closely related to the finite-horizon H∞ performance. Moreover, the time-varying controller parameters are characterized via solving coupled backward recursive Riccati difference equations (RDEs). A simulation example is utilized to illustrate the usefulness of the proposed controller design scheme
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An investigation into standards in sustainable design and manufacture
This paper reports upon the application of standards to reduce the negative environmental impacts of manufacturing through product lifecycle planning and closed loop production. By eliminating waste and retaining the energy embodied within materials and components, manufacturing can become more sustainable from both ecological and financial perspectives. Energy consumption and the associated carbon pollution can thus be minimised. Environmental Management System implementation is also considered
High efficiency coherent optical memory with warm rubidium vapour
By harnessing aspects of quantum mechanics, communication and information
processing could be radically transformed. Promising forms of quantum
information technology include optical quantum cryptographic systems and
computing using photons for quantum logic operations. As with current
information processing systems, some form of memory will be required. Quantum
repeaters, which are required for long distance quantum key distribution,
require optical memory as do deterministic logic gates for optical quantum
computing. In this paper we present results from a coherent optical memory
based on warm rubidium vapour and show 87% efficient recall of light pulses,
the highest efficiency measured to date for any coherent optical memory. We
also show storage recall of up to 20 pulses from our system. These results show
that simple warm atomic vapour systems have clear potential as a platform for
quantum memory
An AC Stark Gradient Echo Memory in Cold Atoms
The burgeoning fields of quantum computing and quantum key distribution have
created a demand for a quantum memory. The gradient echo memory scheme is a
quantum memory candidate for light storage that can boast efficiencies
approaching unity, as well as the flexibility to work with either two or three
level atoms. The key to this scheme is the frequency gradient that is placed
across the memory. Currently the three level implementation uses a Zeeman
gradient and warm atoms. In this paper we model a new gradient creation
mechanism - the ac Stark effect - to provide an improvement in the flexibility
of gradient creation and field switching times. We propose this scheme in
concert with a move to cold atoms (~1 mK). These temperatures would increase
the storage times possible, and the small ensemble volumes would enable large
ac Stark shifts with reasonable laser power. We find that memory bandwidths on
the order of MHz can be produced with experimentally achievable laser powers
and trapping volumes, with high precision in gradient creation and switching
times on the order of nanoseconds possible. By looking at the different
decoherence mechanisms present in this system we determine that coherence times
on the order of 10s of milliseconds are possible, as are delay-bandwidth
products of approximately 50 and efficiencies over 90%
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