Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comment on "Quantum Time Crystals from Hamiltonians with Long-Range
  Interactions"   In a recent paper (Phys. Rev. Lett. 123, 210602), Kozin and Kyriienko claim
to realize "genuine" ground state time crystals by studying models with
long-ranged and infinite-body interactions. Here we point out that their models
are doubly problematic: they are unrealizable ${\it and}$ they violate well
established principles for defining phases of matter. Indeed with infinite body
operators allowed, almost all quantum systems are time crystals. In addition,
one of their models is highly unstable and another amounts to isolating, via
fine tuning, a single degree of freedom in a many body system--allowing for
this elevates the pendulum of Galileo and Huygens to a genuine time crystal.

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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: cs
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc