Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photon echoes using atomic frequency combs in Pr:YSO -- experiment and
  semiclassical theory   Photon echoes in rare-earth-doped crystals are studied to understand the
challenges of making broadband quantum memories using the atomic frequency comb
(AFC) protocol in systems with hyperfine structure. The hyperfine structure of
Pr$^{3+}$ poses an obstacle to this goal because frequencies associated with
the hyperfine transitions change the simple picture of modulation at an
externally imposed frequency. The current work focuses on the intermediate case
where the hyperfine spacing is comparable to the comb spacing, a challenging
regime that has recently been considered. This may facilitate storing quantum
information over a larger spectral range in such systems. In this work, we
prepare broadband AFCs using optical combs with tooth spacings ranging from 1
MHz to 16 MHz in fine steps, and measure transmission spectra and photon echoes
for each. We predict the spectra and echoes theoretically using the optical
combs as input to a density matrix code, which calculates the redistribution of
populations. We then use the redistributed populations as input to a
semiclassical theory using the frequency-dependent dielectric function. This
approach gives a good account of the first and second photon echoes and can be
applied to other rare-earth systems.

9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat