5,062 research outputs found
Coherent optical implementations of the fast Fourier transform and their comparison to the optical implementation of the quantum Fourier transform
Optical structures to implement the discrete Fourier transform (DFT) and fast Fourier transform (FFT) algorithms for discretely sampled data sets are considered. In particular, the decomposition of the FFT algorithm into the basic Butterfly operations is described, as this allows the algorithm to be fully implemented by the successive coherent addition and subtraction of two wavefronts (the subtraction being performed after one has been appropriately phase shifted), so facilitating a simple and robust hardware implementation based on waveguided hybrid devices as employed in coherent optical detection modules. Further, a comparison is made to the optical structures proposed for the optical implementation of the quantum Fourier transform and they are shown to be very similar
Curvature fluctuations on asymptotically de Sitter spacetimes via the semiclassical Einstein's equations
It has been proposed recently to consider in the framework of cosmology an
extension of the semiclassical Einstein's equations in which the Einstein
tensor is considered as a random function. This paradigm yields a hierarchy of
equations between the -point functions of the quantum, normal ordered,
stress energy-tensor and those associated to the stochastic Einstein tensor.
Assuming that the matter content is a conformally coupled massive scalar field
on de Sitter spacetime, this framework has been applied to compute the power
spectrum of the quantum fluctuations and to show that it is almost
scale-invariant. We test the robustness and the range of applicability of this
proposal by applying it to a less idealized, but physically motivated,
scenario, namely we consider Friedmann-Robertson-Walker spacetimes which behave
only asymptotically in the past as a de Sitter spacetime. We show in particular
that, under this new assumption and independently from any renormalization
freedom, the power spectrum associated to scalar perturbations of the metric
behaves consistently with an almost scale-invariant power spectrum.Comment: 23 page
Massive Parallel Quantum Computer Simulator
We describe portable software to simulate universal quantum computers on
massive parallel computers. We illustrate the use of the simulation software by
running various quantum algorithms on different computer architectures, such as
a IBM BlueGene/L, a IBM Regatta p690+, a Hitachi SR11000/J1, a Cray X1E, a SGI
Altix 3700 and clusters of PCs running Windows XP. We study the performance of
the software by simulating quantum computers containing up to 36 qubits, using
up to 4096 processors and up to 1 TB of memory. Our results demonstrate that
the simulator exhibits nearly ideal scaling as a function of the number of
processors and suggest that the simulation software described in this paper may
also serve as benchmark for testing high-end parallel computers.Comment: To appear in Comp. Phys. Com
Toward an architecture for quantum programming
It is becoming increasingly clear that, if a useful device for quantum
computation will ever be built, it will be embodied by a classical computing
machine with control over a truly quantum subsystem, this apparatus performing
a mixture of classical and quantum computation.
This paper investigates a possible approach to the problem of programming
such machines: a template high level quantum language is presented which
complements a generic general purpose classical language with a set of quantum
primitives. The underlying scheme involves a run-time environment which
calculates the byte-code for the quantum operations and pipes it to a quantum
device controller or to a simulator.
This language can compactly express existing quantum algorithms and reduce
them to sequences of elementary operations; it also easily lends itself to
automatic, hardware independent, circuit simplification. A publicly available
preliminary implementation of the proposed ideas has been realized using the
C++ language.Comment: 23 pages, 5 figures, A4paper. Final version accepted by EJPD ("swap"
replaced by "invert" for Qops). Preliminary implementation available at:
http://sra.itc.it/people/serafini/quantum-computing/qlang.htm
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