1,625 research outputs found
To be a realist about quantum theory
I look at the distinction between between realist and antirealist views of the quantum state. I argue that this binary classification should be reconceived as a continuum of different views about which properties of the quantum state are representationally significant. What's more, the extreme cases -- all or none --- are simply absurd, and should be rejected by all parties. In other words, no sane person should advocate extreme realism or antirealism about the quantum state. And if we focus on the reasonable views, it's no longer clear who counts as a realist, and who counts as an antirealist. Among those taking a more reasonable intermediate view, we find figures such as Bohr and Carnap -- in stark opposition to the stories we've been told
Local quanta, unitary inequivalence, and vacuum entanglement
In this work we develop a formalism for describing localised quanta for a
real-valued Klein-Gordon field in a one-dimensional box . We quantise
the field using non-stationary local modes which, at some arbitrarily chosen
initial time, are completely localised within the left or the right side of the
box. In this concrete set-up we directly face the problems inherent to a notion
of local field excitations, usually thought of as elementary particles.
Specifically, by computing the Bogoliubov coefficients relating local and
standard (global) quantizations, we show that the local quantisation yields a
Fock space which is unitarily inequivalent to the standard one
. In spite of this, we find that the local creators and
annihilators remain well defined in the global Fock space , and
so do the local number operators associated to the left and right partitions of
the box. We end up with a useful mathematical toolbox to analyse and
characterise local features of quantum states in . Specifically,
an analysis of the global vacuum state in terms
of local number operators shows, as expected, the existence of entanglement
between the left and right regions of the box. The local vacuum
, on the contrary, has a very different character.
It is neither cyclic nor separating and displays no entanglement. Further
analysis shows that the global vacuum also exhibits a distribution of local
excitations reminiscent, in some respects, of a thermal bath. We discuss how
the mathematical tools developed herein may open new ways for the analysis of
fundamental problems in local quantum field theory.Comment: 28 pages, 8 figure
An Introduction to Quantum Computing for Non-Physicists
Richard Feynman's observation that quantum mechanical effects could not be
simulated efficiently on a computer led to speculation that computation in
general could be done more efficiently if it used quantum effects. This
speculation appeared justified when Peter Shor described a polynomial time
quantum algorithm for factoring integers.
In quantum systems, the computational space increases exponentially with the
size of the system which enables exponential parallelism. This parallelism
could lead to exponentially faster quantum algorithms than possible
classically. The catch is that accessing the results, which requires
measurement, proves tricky and requires new non-traditional programming
techniques.
The aim of this paper is to guide computer scientists and other
non-physicists through the conceptual and notational barriers that separate
quantum computing from conventional computing. We introduce basic principles of
quantum mechanics to explain where the power of quantum computers comes from
and why it is difficult to harness. We describe quantum cryptography,
teleportation, and dense coding. Various approaches to harnessing the power of
quantum parallelism are explained, including Shor's algorithm, Grover's
algorithm, and Hogg's algorithms. We conclude with a discussion of quantum
error correction.Comment: 45 pages. To appear in ACM Computing Surveys. LATEX file. Exposition
improved throughout thanks to reviewers' comment
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