Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical coherence of $^{166}$Er:$^{7}$LiYF$_4$ crystal below 1 Kelvin   We explore spin dynamics of isotopically purified $^{166}$Er:$^{7}$LiYF$_4$
crystal below 1 Kelvin and at weak magnetic fields $<$0.3 T. Crystals grown in
our lab demonstrate record-narrow inhomogeneous optical broadening down to
16~MHz. Solid state atomic ensembles with such narrow linewidths are very
attractive for the implementation of off-resonant Raman quantum memory and for
the interfacing of superconducting quantum circuits and telecom C-band optical
photons. Both applications require low magnetic field of $\sim10$ mT. However,
at conventional experimental temperatures $T>1.5$ K and time scales of $\mu$s,
spin coherence of Er:LYF crystal appears only at magnetic fields above 1 Tesla.
In the present work, we demonstrate spin coherence of Er:LYF crystals at the
field range compatible with ZEFOZ transitions of $^{167}$Er isotope and with
working conditions of superconducting quantum circuits.

20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex