Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: States of an Ensemble of Two-Level Atoms with Reduced Quantum
  Uncertainty   We generate entangled states of an ensemble of 5*10^4 rubidium-87 atoms by
optical quantum nondemolition measurement. The resonator-enhanced measurement
leaves the atomic ensemble, prepared in a superposition of hyperfine clock
levels, in a squeezed spin state. By comparing the resulting reduction of
quantum projection noise (up to 8.8(8) dB) with the concomitant reduction of
coherence, we demonstrate a clock input state with spectroscopic sensitivity
3.0(8) dB beyond the standard quantum limit.

32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph