Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Clifford Quantum Cellular Automata: Trivial group in 2D and Witt group
  in 3D   We study locality preserving automorphisms of operator algebras on
$D$-dimensional uniform lattices of prime $p$-dimensional qudits (QCA),
specializing in those that are translation invariant (TI) and map every prime
$p$-dimensional Pauli matrix to a tensor product of Pauli matrices (Clifford).
We associate antihermitian forms of unit determinant over Laurent polynomial
rings to TI Clifford QCA with lattice boundaries, and prove that the form
determines the QCA up to Clifford circuits and shifts (trivial). It follows
that every 2D TI Clifford QCA is trivial since the antihermitian form in this
case is always trivial. Further, we prove that for any $D$ the fourth power of
any TI Clifford QCA is trivial.
  We present explicit examples of nontrivial TI Clifford QCA for $D=3$ and any
odd prime $p$, and show that the Witt group of the finite field $\mathbb F_p$
is a subgroup of the group $\mathfrak C(D = 3, p)$ of all TI Clifford QCA
modulo trivial ones. That is, $\mathfrak C(D = 3, p \equiv 1 \mod 4) \supseteq
\mathbb Z_2 \times \mathbb Z_2$ and $\mathfrak C(D = 3, p \equiv 3 \mod 4)
\supseteq \mathbb Z_4$. The examples are found by disentangling the ground
state of a commuting Pauli Hamiltonian which is constructed by coupling layers
of prime dimensional toric codes such that an exposed surface has an anomalous
topological order that is not realizable by commuting Pauli Hamiltonians
strictly in two dimensions.
  In an appendix independent of the main body of the paper, we revisit a recent
theorem of Freedman and Hastings that any two-dimensional QCA, which is not
necessarily Clifford or translation invariant, is a constant depth quantum
circuit followed by a shift. We give a more direct proof of the theorem without
using any ancillas.

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The categories of this paper are: alg-geom
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
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The categories of this paper are: astro-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org