Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The quantum Allan variance   The instability of an atomic clock is characterized by the Allan variance, a
measure widely used to describe the noise of frequency standards. We provide an
explicit method to find the ultimate bound on the Allan variance of an atomic
clock in the most general scenario where N atoms are prepared in an arbitrarily
entangled state and arbitrary measurement and feedback are allowed, including
those exploiting coherences between succeeding interrogation steps. While the
method is rigorous and general, it becomes numerically challenging for large N
and long averaging times.

5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys