Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Single-photon interferometry and spectroscopy with two laser frequency
  combs   We demonstrate single-photon time-domain interference in a new realm. We
observe interferences in the photon counting statistics with two separate
mode-locked femtosecond lasers of slightly different repetition frequencies,
each emitting a comb of evenly spaced spectral lines over a wide spectral span.
We exploit the interference pattern for spectroscopic diagnostics over a broad
spectral range. An experimental proof-of-concept shows that the emerging
technique of high-resolution dual-comb Fourier transform spectroscopy can be
performed at light powers that are a billion-fold weaker than those commonly
employed. Our experiments challenge the intuitive concept that a photon exists
before detection and they open the prospect of precise spectroscopy over broad
spectral bandwidth in light-starved conditions.

10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
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
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat