Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Noiseless Quantum Codes   In this paper we study a model quantum register $\cal R$ made of $N$ replicas
(cells) of a given finite-dimensional quantum system S. Assuming that all cells
are coupled with a common environment with equal strength we show that, for $N$
large enough, in the Hilbert space of $\cal R$ there exists a linear subspace
${\cal C}_N$ which is dynamically decoupled from the environment. The states in
${\cal C}_N$ evolve unitarily and are therefore decoherence-dissipation free.
The space ${\cal C}_N$ realizes a noiseless quantum code in which information
can be stored, in principle, for arbitrarily long time without being affected
by errors.

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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph