Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental demonstration of phase measurement precision beating
  standard quantum limit by projection measurement   We propose and demonstrate experimentally a projection scheme to measure the
quantum phase with a precision beating the standard quantum limit. The initial
input state is a twin Fock state $|N,N>$ proposed by Holland and Burnett [Phys.
Rev. Lett. {\bf 71}, 1355 (1993)] but the phase information is extracted by a
quantum state projection measurement. The phase precision is about $1.4/N$ for
large photon number $N$, which approaches the Heisenberg limit of 1/N.
Experimentally, we employ a four-photon state from type-II parametric
down-conversion and achieve a phase uncertainty of $0.291\pm 0.001$ beating the
standard quantum limit of $1/\sqrt{N} = 1/2$ for four photons.

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The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat