211,376 research outputs found
Emergent quantum state designs from individual many-body wavefunctions
Quantum chaos in many-body systems provides a bridge between statistical and
quantum physics with strong predictive power. This framework is valuable for
analyzing properties of complex quantum systems such as energy spectra and the
dynamics of thermalization. While contemporary methods in quantum chaos often
rely on random ensembles of quantum states and Hamiltonians, this is not
reflective of most real-world systems. In this paper, we introduce a new
perspective: across a wide range of examples, a single non-random quantum state
is shown to encode universal and highly random quantum state ensembles. We
characterize these ensembles using the notion of quantum state -designs from
quantum information theory and investigate their universality using a
combination of analytic and numerical techniques. In particular, we establish
that -designs arise naturally from generic states as well as individual
states associated with strongly interacting, time-independent Hamiltonian
dynamics. Our results offer a new approach for studying quantum chaos and
provide a practical method for sampling approximately uniformly random states;
the latter has wide-ranging applications in quantum information science from
tomography to benchmarking.Comment: 7+19 pages, 6 figure
The Internet as a Diversion
Presents survey findings on the extent to which people who use online sources of economic and financial information also use the Internet to take their minds off of the recession. Analyzes data by online activity, age, gender, and financial situation
A Complete Theory of Everything (will be subjective)
Increasingly encompassing models have been suggested for our world. Theories
range from generally accepted to increasingly speculative to apparently bogus.
The progression of theories from ego- to geo- to helio-centric models to
universe and multiverse theories and beyond was accompanied by a dramatic
increase in the sizes of the postulated worlds, with humans being expelled from
their center to ever more remote and random locations. Rather than leading to a
true theory of everything, this trend faces a turning point after which the
predictive power of such theories decreases (actually to zero). Incorporating
the location and other capacities of the observer into such theories avoids
this problem and allows to distinguish meaningful from predictively meaningless
theories. This also leads to a truly complete theory of everything consisting
of a (conventional objective) theory of everything plus a (novel subjective)
observer process. The observer localization is neither based on the
controversial anthropic principle, nor has it anything to do with the
quantum-mechanical observation process. The suggested principle is extended to
more practical (partial, approximate, probabilistic, parametric) world models
(rather than theories of everything). Finally, I provide a justification of
Ockham's razor, and criticize the anthropic principle, the doomsday argument,
the no free lunch theorem, and the falsifiability dogma.Comment: 26 LaTeX page
Benchmarking integrated photonic architectures
Photonic platforms represent a promising technology for the realization of
several quantum communication protocols and for experiments of quantum
simulation. Moreover, large-scale integrated interferometers have recently
gained a relevant role for restricted models of quantum computing, specifically
with Boson Sampling devices. Indeed, various linear optical schemes have been
proposed for the implementation of unitary transformations, each one suitable
for a specific task. Notwithstanding, so far a comprehensive analysis of the
state of the art under broader and realistic conditions is still lacking. In
the present work we address this gap, providing in a unified framework a
quantitative comparison of the three main photonic architectures, namely the
ones with triangular and square designs and the so-called fast transformations.
All layouts have been analyzed in presence of losses and imperfect control over
the reflectivities and phases of the inner structure. Our results represent a
further step ahead towards the implementation of quantum information protocols
on large-scale integrated photonic devices.Comment: 10 pages, 6 figures + 2 pages Supplementary Informatio
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