Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Absolute Measurement of Quantum-Limited Interferometric Displacements   A methodology is introduced that enables an absolute, quantum-limited
measurement of sub-wavelength interferometric displacements. The technique
utilizes a high-frequency optical path modulation within an interferometer
operated in a homodyne configuration. All of the information necessary to fully
characterize the resultant path displacement is contained within the relative
strengths of the various harmonics of the phase modulation. The method, which
is straightforward and readily implementable, allows a direct measurement of
the theoretical Cram\'er-Rao limit of detection without any assumptions on the
nature of the light source.

34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ